Flax (Linum usitatissimum L.) Fibers for Composite Reinforcement: Exploring the Link Between Plant Growth, Cell Walls Development, and Fiber Properties

Due to the combination of high mechanical performances and plant-based origin, flax fibers are interesting reinforcement for environmentally friendly composite materials. An increasing amount of research articles and reviews focuses on the processing and properties of flax-based products, without taking into account the original key role of flax fibers, namely, reinforcement elements of the flax stem (Linum usitatissimum L.). The ontogeny of the plant, scattering of fiber properties along the plant, or the plant growth conditions are rarely considered. Conversely, exploring the development of flax fibers and parameters influencing the plant mechanical properties (at the whole plant or fiber scale) could be an interesting way to control and/or optimize fiber performances, and to a greater extent, flax fiber-based products. The first part of the present review synthesized the general knowledge about the growth stages of flax plants and the internal organization of the stem biological tissues. Additionally, key findings regarding the development of its fibers, from elongation to thickening, are reviewed to offer a piece of explanation of the uncommon morphological properties of flax fibers. Then, the slenderness of flax is illustrated by comparison of data given in scientific research on herbaceous plants and woody ones. In the second section, a state of the art of the varietal selection of several main industrial crops is given. This section includes the different selection criteria as well as an overview of their impact on plant characteristics. A particular interest is given to the lodging resistance and the understanding of this undesired phenomenon. The third section reviews the influence of the cultural conditions, including seedling rate and its relation with the wind in a plant canopy, as well as the impact of main tropisms (namely, thigmotropism, seismotropism, and gravitropism) on the stem and fiber characteristics. This section illustrates the mechanisms of plant adaptation, and how the environment can modify the plant biomechanical properties. Finally, this review asks botanists, breeders, and farmers’ knowledge toward the selection of potential flax varieties dedicated to composite applications, through optimized fiber performances. All along the paper, both fibers morphology and mechanical properties are discussed, in constant link with their use for composite materials reinforcement.

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title: Flax fibre and its composites – A review
abstract: In recent years, the use of flax fibres as reinforcement in composites has gained popularity due to an increasing requirement for developing sustainable materials. Flax fibres are cost-effective and offer specific mechanical properties comparable to those of glass fibres. Composites made of flax fibres with thermoplastic, thermoset, and biodegradable matrices have exhibited good mechanical properties. This review presents a summary of recent developments of flax fibre and its composites. Firstly, the fibre structure, mechanical properties, cost, the effect of various parameters (i.e. relative humidity, various physical/chemical treatments, gauge length, fibre diameter, fibre location in a stem, oleaginous, mechanical defects such as kink bands) on tensile properties of flax fibre have been reviewed. Secondly, the effect of fibre configuration (i.e. in forms of fabric, mat, yarn, roving and monofilament), manufacturing processes, fibre volume, and fibre/matrix interface parameters on the mechanical properties of flax fibre reinforced composites have been reviewed. Next, the studies of life cycle assessment and durability investigation of flax fibre reinforced composites have been reviewed.

title: A review of recent developments in natural fibre composites and their mechanical performance
abstract: Recently, there has been a rapid growth in research and innovation in the natural fibre composite (NFC) area. Interest is warranted due to the advantages of these materials compared to others, such as synthetic fibre composites, including low environmental impact and low cost and support their potential across a wide range of applications. Much effort has gone into increasing their mechanical performance to extend the capabilities and applications of this group of materials. This review aims to provide an overview of the factors that affect the mechanical performance of NFCs and details achievements made with them.

title: Tensile properties of elementary fibres of flax and glass: Analysis of reproducibility and scattering
abstract: Tensile properties of 13 batches of flax fibres (Marylin variety) grown over 4 years with 4 different climatic conditions were compared with 4 batches of glass fibres. It was found that tensile properties of elementary flax fibres were reproducible despite drought or an excess of water. The values of strength and strain at break of commercial glass fibres were found to be as scattered as the flax fibres ones. It was concluded that flax fibres are suitable to replace glass fibres for composite reinforcement.

title: Impregnated fibre bundle test for natural fibres used in composites
abstract: In this study, the impregnated fibre bundle test, a common method used by carbon and glass fibre manufacturers to determine the properties of fibres used in composites, was adapted for natural fibres and validated by a round robin test on one type of natural fibres, namely flax fibres. Five European laboratories have carried out in parallel the impregnated fibre bundle test, on the same batch of hackled flax (long fibres), to check the applicability and reliability of this modified method on natural fibres. The results were compared to the more traditional single fibre test on elementary fibres. The back-calculated fibre stiffness shows a very low scatter between the five laboratories of less than ±5% (59.8 ± 2.4 GPa, as measured between 0 and 0.1% strain). The fibre ultimate tensile strength of 527 ± 138 MPa has a higher scatter, compared to stiffness values, as this property is highly sensitive to imperfections and flaws.

title: Mechanical and acoustic behaviour of porosity controlled randomly dispersed flax/PP biocomposite
abstract: Commingled plant and polypropylene fibres (PP) nonwovens are attractive for automotive industry because of their interesting mechanical performances combined with good acoustical properties. This double function is achieved thanks of controlled porosity within the composite material. Indeed, from a same material, different functions (acoustic or mechanical) can be obtained by only varying the compaction rate during moulding. This study aims to highlight the necessity of a very large porosity volume fraction (60%) to reach good acoustic properties and understand the mechanical effect behind it. By combining tensile testing, acoustic absorption measurement and scanning electron imaging analysis, the microstructure, acoustic and mechanical properties have been investigated and were found to be intimately related to the material porosity content. As expected, when increasing porosity level from 5 to 60%, the material behaviour change and its tensile properties (modulus, strength and elasticity domain) drop drastically to a point where the material is no longer elastic (70% porosity) due to a modification of the material microstructure involving different failure mechanisms.

title: Compaction of textile reinforcements for composites manufacturing. III: Reorganization of the fiber network
abstract: The objectives of this series of papers are to describe the mechanical behavior of textile reinforcements under normal load and to quantify the effects of diverse processing parameters on that behavior. In the first and second papers of the series, experimental compaction and relaxation results were reported; general trends were identified and the effects of changes in the processing parameters were analyzed. In this paper, the results of sequences of successive compaction cycles applied to dry textiles and to textiles saturated in distilled H 2 O and silicone oil are presented. The reinforcements investigated are produced by assembling tows or rovings following different patterns; it is shown that the resulting heterogeneity, or regular variation of the local fiber volume fraction, can be associated to some particular elements of the mechanical behavior of the reinforcements. The reorganization of the fiber network and the effect of friction at the fiber contacts are demonstrated. Different stages in the reorganization process are identified; each stage is controlled by different parameters and corresponds to a precise behavior. Successive compaction cycles applied to a preform can reduce the void content of the final part.

title: Flax/polypropylene composites for lightened structures: Multiscale analysis of process and fibre parameters
abstract: The optimization of the processing method for poly-(propylene) (PP)/plant fibre composites compounding is a key point in the development of semi-structural parts, especially for automotive applications. The aim of this original and innovating work is to study, at different scales, the impact of extrusion equipment and fibre length on the composite's mechanical performances. Firstly, we studied the flax fibre morphology after compounding and injection as well as their individualization in injected specimens. Secondly, we focused on the effects they had on tensile properties. The impact of the processing tool was observed on fibre morphology and division; as well as the use of a BUSS system instead of a twin-screw extruder, which enhances the fibre individualization, however, the number of kneading areas should be reduced in order to preserve the reinforcement aspect ratio. We highlight the fact that the composite's mechanical performances are highly impacted by the fibre division and cell wall stiffness, as demonstrated by in-situ nanoindentation tests. Finally, the use of longer fibres is not a priority for the improvement of mechanical performances; it induces a more difficult fibre division and an increase in the compound viscosity, which could endanger the moulding process of the final part.

title: The effect of reprocessing on the mechanical properties of polypropylene reinforced with wood pulp, flax or glass fibre
abstract: Composites of polypropylene, substitutable for a given application and reinforced with: Medium Density Fibreboard fibre (MDF) (40 wt%); flax (30 wt%); and glass fibre (20 wt%), were evaluated after 6 injection moulding and extrusion reprocessing cycles. Of the range of tensile, flexural and impact properties examined, MDF composites showed the best mean property retention after reprocessing (87%) compared to flax (72%) and glass (59%). After 1 reprocessing cycle the glass composite had higher tensile strength (56.2 MPa) compared to the MDF composite (44.4) but after 6 cycles the MDF was stronger (35.0 compared to 29.6 MPa for the glass composite). Property reductions were attributed to reduced fibre length. MDF fibres showed the lowest reduction in fibre length between 1 and 6 cycles (39%), compared to glass (51%) and flax (62%). Flax fibres showed greater increases in damage (cell wall dislocations) with reprocessing than was shown by MDF fibres.

title: Interfacial shear strength of flax fiber/thermoset polymers estimated by fiber fragmentation tests
abstract: We study flax/thermoset polymer ISS [interfacial shear strength] for most common types of thermosets: vinylester, polyester, and epoxy. The effect of fiber surface treatment on ISS in such systems ...

title: Thermoset lactic acid‐based resin as a matrix for flax fibers
abstract: Thermoset composites were produced from flax fibers and a novel lactic acid (LA)-based thermoset resin. This resin is based on methacrylated, star-shaped oligomers of LA. The main purpose ...

title: Tensile and compressive damaged response in Flax fibre reinforced epoxy composites
abstract: Composite reinforcement by natural fibres like Flax do not enjoy the same popularity in engineering design as Carbon or Glass fibres on account of the relatively immature mechanical data on Flax-composites. Tensile and compressive mechanical properties are determined for Flax-fibre-reinforced-Epoxy composite. Damaged response is followed through SEM observations and by measuring evolving stiffness and permanent deformation. Specimens are repeatedly loaded-unloaded at progressively increasing maximum loads until failure, allowing a quantitative description of in-plane modulus and inelasticity evolution. Stiffness degradation rates do not necessarily correlate with inelastic straining rates, and modulus may remain unchanged while still accumulating inelastic strains – therefore both modulus and inelastic strain need evaluating to fully describe the material damaged response. Damage initiates within the fibre or at fibre-matrix interface; matrix-related damage appears not critical to damage initiation and progression. The reported data is valuable for the development of predictive models of damaged-condition response in Flax-epoxy structures.

title: A review of bast fibres and their composites. Part 1 – Fibres as reinforcements
abstract: Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants. The fibres find use in textile applications and are increasingly being considered as reinforcements for polymer–matrix composites as they are perceived to be “sustainable”. The fibres are composed primarily of cellulose which potentially has a Young’s modulus of ∼140 GPa (being a value comparable with man-made aramid [Kevlar/Twaron] fibres). The plants which are currently attracting most interest are flax and hemp (in temperate climates) or jute and kenaf (in tropical climates). This review paper will consider the growth, harvesting and fibre separation techniques suitable to yield fibre of appropriate quality. The text will then address characterisation of the fibre as, unlike man-made fibres, the cross section is neither circular nor uniform along the length.

title: A review on the tensile properties of natural fiber reinforced polymer composites
abstract: This paper is a review on the tensile properties of natural fiber reinforced polymer composites. Natural fibers have recently become attractive to researchers, engineers and scientists as an alternative reinforcement for fiber reinforced polymer (FRP) composites. Due to their low cost, fairly good mechanical properties, high specific strength, non-abrasive, eco-friendly and bio-degradability characteristics, they are exploited as a replacement for the conventional fiber, such as glass, aramid and carbon. The tensile properties of natural fiber reinforce polymers (both thermoplastics and thermosets) are mainly influenced by the interfacial adhesion between the matrix and the fibers. Several chemical modifications are employed to improve the interfacial matrix–fiber bonding resulting in the enhancement of tensile properties of the composites. In general, the tensile strengths of the natural fiber reinforced polymer composites increase with fiber content, up to a maximum or optimum value, the value will then drop. However, the Young’s modulus of the natural fiber reinforced polymer composites increase with increasing fiber loading. Khoathane et al.  found that the tensile strength and Young’s modulus of composites reinforced with bleached hemp fibers increased incredibly with increasing fiber loading. Mathematical modelling was also mentioned. It was discovered that the rule of mixture (ROM) predicted and experimental tensile strength of different natural fibers reinforced HDPE composites were very close to each other. Tsai equation was found to be the most effective equation in predicting the Young’s modulus of composites containing different types of natural fibers.

title: Evidence of the domestication history of flax (Linum usitatissimum L.) from genetic diversity of the sad2 locus
abstract: A phylogenetic analysis was conducted on 34 alleles of 2.5 kb sized stearoyl-ACP desaturase II (sad2), obtained from 30 accessions of cultivated and pale flax (Linum spp.), to elucidate the history of flax domestication. The analysis supports a single domestication origin for extant cultivated flax. The phylogenetic evidence indicates that flax was first domesticated for oil, rather than fibre. The genetic diversity of the sad2 locus in cultivated flax is low when compared to that of the pale flax assayed. An absolute archaeological date could be applied to the synonymous substitution rate of sad2 in cultivated flax, yielding a high estimate of 1.60–1.71×10−7 substitutions/site/year. The occurrence of nonsynonymous substitutions at conserved positions of the third exon in alleles from cultivated flax suggests that the locus may have been subjected to an artificial selection pressure. The elevated synonymous substitution rate is also compatible with a population expansion of flax since domestication, followed by a population decline in historic times. These findings provide new insight into flax domestication and are significant for the continuous exploration of the flax germplasm for utilization.

title: Cellulosic Fibers: Role of Matrix Polysaccharides in Structure and Function
abstract: Cellulose, being the major cell wall component and the most abundant organic matter, produced by living organisms, is not uniformly distributed within plant tissues. There are numerous cells, like the parenchyma ones, which even at maturity have thin cell wall. Thick cell walls are characteristic for the tissues with mechanical function. Among those, there are cell walls, which contain several major components, and those, the predominant component of which is cellulose. The most pure natural cellulose is considered to be present in cotton seed hairs (sometimes erroneously called “cotton fibers”) – over 90% of cell wall . Very close to this value is a special group of plant fibers – cellulosic or gelatinous fibers, the proportion of cellulose in which amounts for 85-90% [2,3]. The cell wall thickness in such fibers may reach 15 m, as compared to 0.2 m in cells with thin cell wall. So, the very significant portion of total plant cellulose may be concentrated within the gelatinous fibers, making them the important source for production of biofuels and bio-based products. An additional attractiveness of cellulosic fibers for such applications comes from the fact that gelatinous cell wall layers are devoid of lignin – the major hurdle in using plant biomass .

title: Cell-Wall Polysaccharides of Developing Flax Plants
abstract: Flax (Linum usitatissimum L.) fibers originate from procambial cells of the protophloem and develop in cortical bundles that encircle the vascular cylinder. We determined the polysaccharide composition of the cell walls from various organs of the developing flax plant, from fiber-rich strips peeled from the stem, and from the xylem. Ammonium oxalate-soluble polysaccharides from all tissues contained 5-linked arabinans with low degrees of branching, rhamnogalacturonans, and polygalacturonic acid. The fiber-rich peels contained, in addition, substantial amounts of a buffer-soluble, 4-linked galactan branched at the 0–2 and 0–3 positions with nonreducing terminal-galactosyl units. The cross-linking glycans from all tissues were (fucogalacto)xyloglucan, typical of type-I cell walls, xylans containing (1->)-[beta]-D-xylosyl units branched exclusively at the xylosyl O-2 with t-(4-O-methyl)-glucosyluronic acid units, and (galacto)glucomannans. Tissues containing predominantly primary cell wall contained a larger proportion of xyloglucan. The xylem cells were composed of about 60% 4-xylans, 32% cellulose, and small amounts of pectin and the other cross-linking polysaccharides. The noncellulosic polysaccharides of flax exhibit an uncommonly low degree of branching compared to similar polysaccharides from other flowering plants. Although the relative abundance of the various noncellulosic polysaccharides varies widely among the different cell types, the linkage structure and degree of branching of several of the noncellulosic polysaccharides are invariant.

title: Average tensile properties of French elementary flax fibers
abstract: In a composite ecodesign approach, flax fibers could be good candidates for glass fiber substitution. However, their use in industrial applications could be restricted due to their scattered mechanical properties. In this study, we compared tensile properties of 50 batches of flax (Linum usitatissimum) fibers, cultivated in France between 1993 and 2011. Thus, 2954 fibers were tested in the same conditions according to the XP T 25-501-2 standard. Reliable specific data are suggested to be a basis for design calculation.

title: Flax stems: from a specific architecture to an instructive model for bioinspired composite structures.
abstract: The present paper proposes to carefully study and describe the reinforcement mechanisms within a flax stem, which is an exceptional natural model of composite structure. Thanks to accurate microscopic investigations, with both optical and SEM method, we finely depicted the flax stem architecture, which can be view as a composite structure with an outer protection, a unidirectional ply on the periphery and a porous core; each component has a specific function, such as mechanical reinforcement for the unidirectional ply and the porous core. The significant mechanical role of fibres was underlined, as well as their local organisation in cohesive bundles, obtained because of an intrusive growth and evidenced in this work through nanomechanical AFM measurement and 3D reconstruction. Following a biomimetic approach, these data provide a source of inspiration for the composite materials of tomorrow.

title: A uniform decimal code for growth stages of crops and weeds
abstract: A universal scale (to be known as the BBCH scale) using a decimal code for the description of the growth stages of most agricultural crops and weeds is proposed. The scale and codes are based on the well-known Zadoks code for cereals. 
 
Developmentally similar growth stages of different crops are given the same codes. The general scale provides a framework within which more specific scales for individual crops may be constructed. The uniformity of the scale makes it easy to remember and use in agricultural practice and simplifies storage and retrieval in a computer system. 
 
A description of the general scale is given followed by specific scales for cereals, rice, maize, oilseed rape, field beans, peas and sunflower. Comparisons with scales currently in use are given where appropriate.

title: Decimal code for growth stages of hemp (Cannabis sativa L.)
abstract: A decimal code for hemp (Cannabis sativa L.) growth stages is presented. Life cycle is divided into four principal stages: germination and emergence, vegetation, flowering and seed formation, senescence. Each principal stage is subdivided into secondary stages. The practical use of the code is discussed with particular reference to different yield components.

title: FT Raman microscopy of untreated natural plant fibres.
abstract: The application of FT-Raman microscopy to the non-destructive analysis of natural plant fibres is demonstrated with samples of flax, jute, ramie, cotton, kapok, sisal and coconut fibre. Vibrational assignments are proposed and characteristic features of each material are presented. Samples were not pre-treated chemically before analysis and were used directly from their respective storage collection; the adaptation of the Raman microscopic technique to the identification of specimens of natural fibres in archaeological burial sites is explored for its forensic potential.

title: The snap point: a transition point in Linum usitatissimum bast fiber development
abstract: The developing stem of fibre flax (Linum usitatissimum L.) contains a specific region called the ‘snap point’, where the fiber-enriched bast tissues considerably change their mechanical properties. The snap point was found to be present during a restricted period of plant development */the fast growth phase, and to disappear when stem growth was completed. To relate this snap point to bast fiber formation stages, the number of bast fiber cells and the thickness of their cell walls were followed on the stained cross-sections of the flax stem throughout plant development, using the progressing snap point as the reference. The snap point was shown to be the spot, above which the elongation of bast fiber cells is fully completed. This fast growth stage is the period when the maximum length of all bast fibers in the mature plant (a major characteristic of flax fiber quality) is fixed and would not be changed later. Autoradiography was used to visualize the mode of flax bast fiber elongation above the snap point. The even distribution of label was indicative for surface (diffusive) growth type. Elongation of individual fiber cells was estimated to take only 2 � /4 days with a rate of 1 � /2 cm per day, while cell wall thickening occurs mainly below snap point and lasts around 2 months. The special cell wall structural order, characteristic for mature bast fibers, first appeared at the snap point in the outer layer of the secondary cell wall. Schemes are included, illustrating the course of cell wall thickening and the localization of various stages of fiber formation on the stem of growing flax plant. The established exact localization and duration of flax bast fiber formation stages, and the existence of snap point as the manually identified morphological reference for the transition, permit to separate the bast fibers at different stages of development and make flax an attractive model system to study the functional genomics of fiber formation in technical crops.

title: A comparative study between Europe and China in crop management of two types of flax: linseed and fibre flax
abstract: Presented are the main differences between fibre flax and linseed in the following areas: botany, environmental requirements, methods of cultivation, methods and time of harvesting, and feedstock of potential application in bio-industry. Agricultural practice in fibre flax and linseed cultivation was compared between the EU and China. The subjects of analysis were cultivar choice, environmental requirements, crop rotation place, fertilizers, sowing practices, post emergent cultivation (plant protection) and harvesting. Crucial factors affecting fibre flax and linseed yield and its quality were evaluated. Research gaps were shown for better utilization of potential fibre flax and linseed yielding capacity in the Europe and China.

title: Fiber cell development and fiber yield of flax (Linum usitatissimum L.) affected by the seasonal temperature pattern
abstract: Du, G.-H., Liu, F.-H. and Rowland, G. 2015. Fiber cell development and fiber yield of flax (Linum usitatissimum L.) affected by the seasonal temperature pattern. Can.  Three fiber flax cultivars ‘Ariane’, ‘Argos’ and ‘Viking’ were cultured in growth chambers under three seasonal temperature patterns (STPs) [parabolic (P), anti-parabolic (AP) and quasi-horizontal (QH) configurations]. The effect of STP was studied on fiber cell development and on fiber yield. The results indicated that, compared with the quasi-horizontal seasonal temperature pattern (QH-STP), the size of fiber cell cavity (SFCC) and fiber content (FC) decreased under parabolic seasonal temperature pattern (P-STP). However, the size of fiber cell (SFC) and SFCC decreased, but the number of fiber cells per bundle (NFCB) increased under anti-parabolic seasonal temperature pattern (AP-STP). Moreover, there was a significant positive correlation between fiber weight (FW) and width of fiber bundle (WFB), also between ...

title: The Natural Philosophy of Plant Form
abstract: Preface 1. The meaning and content of plant morphology 2. The plant morphology of the Aristotelian school 3. The plant morphology of Albertus Magnus and Andrea Cesalpino 4. Plant morphology from Joachim Jung to Goethe and de Candolle 5. The concept of the organisation type 6. The partial-shoot theory of the leaf 7. The urge to whole-shoot-hood in the leaf 8. The bearing of the partial-shoot theory of the leaf on other morphological problems 9. Repetitive branching and the gestalt type, with special reference to parallelism 10. The mechanism of plant morphology 11. The interpretation of plant morphology List of books and memoirs cited Index.

title: Plant stems : physiology and functional morphology
abstract: Part 1 Roles of stem architecture in plant performance: plant stems - biomechanical adaption for energy capture and influence on species distributions, T.J. Givnish opportunities and constraints in the placement of flowers and fruits, D.M. Waller and D.A. Steingraeber the biomechanical optimum in woody stems, C. Mattheck shrub stems - form and function, B.F. Wilson. Part 2 Roles of stems in transport and storage of water: limitations on stem water transport and their consequences, J.S. Sperry patterns of xylem variation within a tree and their hydraulic and mechanical consequences, B.L. Gartner stem water storage, N.M. Holbrook. Part 3 Roles of live stem cells in plant performance: role of stems in transport, storage and circulation of ions and metabolites by the whole plant, J.S. Pate and W.D. Jeschke the low profile directors of C- and N-economy in plants - the parenchyma cells associated with translocation channels, A.J.E. van Bel stem photosynthesis - extent, patterns and role in plant carbon economy, E.T. Nilsen microflora and microfauna on stems and trunks - diversity, foodwebs and effects on plants, E.R. Ingham and A.R. Moldenke developmental potential of shoot buds, J.P. Stafstrom respiratory gas exchange and cambial function in tree stems, T.W. Kimmerer and J. Stringer hormonal control of radial and longitudinal growth in the tree stem, C.H.A. Little and R.P. Pharis. Part 4 Roles of stems in preventing or reacting to responses to plant injury: stems and fires, A.M. Gill response of stem growth and function to air pollution, J.A. Weber and N.E. Grulke chemical antiherbivore defense, J.S. Bryant and K.F. Raffa stem defense against pathogens, L. Shain synthesis, T.M. Hinckley and P.S. Schulte.

title: Plant Structure: Function and Development
abstract: plant structure and growth nicholls state university chapter 35: plant structure, growth & development plant structure function and development benjay plant structure function and development nottsent plant structure function and development stirlingaudio plant structure and function plant sciences plant structure, growth, & development a chapter 35: plant structure, growth, and development chapter 35: plant structure, growth, and development chapter 31 plant structure, reproduction, and development an introduction to plant structure and development plant structure, growth, and development etsu homepage plant structure: function and development gbv plant structure, growth, and development sample questions for the biology written comprehensive modeling of spatial structure and development of plants strawberry plant structure and growth habit structure and development of the plant body an overview lecture 7: plant structure and function rutgers university plant structure development fakof chapter 35plant structure and growth part 1 1. vascular plant structure los angeles mission college plant structure, growth and development ch 35 wcjc esau's plant anatomy. meristems, cells, and tissues of the plant structure function and development user manuals by plant structure function and development full download plant structure function and development ebook plant structure and function study guide answer plant structure and function name pre-lab: plant structure and growth umb exercise 3: plant form and function plant structure, growth, and development wikispaces the basic plant cell structure napa valley college chapter 23: plant structure and function robeson.k12 plant structure and function notes ap biology mrs. laux plant anatomy and function the university of vermont name pre-lab: plant structure and growth plant structure worksheet quia structure and function springer plant structure and function workbook answers key plant structure and function answer key xonecs 3rd grade science unit: plant a life ~structure and esaus plant anatomy meristems cells and tissues of the bio 311 plant structure and development semantic scholar course descriptions and function of animal systems (with plant structure, function and adaptation chapter 11 plant structure and function

title: Raven biology of plants, 8th edn
abstract: I first discovered Raven et al.'s Biology of plants (hereafter referred to as BoP) in its 6th edition, published in 1999, when designing a second-year undergraduate ‘botany’ course. Whether it was because this was the first book I'd secured as a free ‘Instructor evaluation copy’ of a textbook (one of the few ‘perks’ of being a university lecturer … ), I can't be sure, but it's been a constant companion, and on my recommended reading list for my plant biology courses (with suitable updating to 2005's 7th edition), ever since. Why? Because it was – and still is! – a great, all-purpose, general plant biology (botany in all but name) text, which includes abundant coloured diagrams, photos and photomicrographs, a substantial glossary (26 two-columned pages), a comprehensive index (64 three-columned pages!), suggestions of further reading (many of which are dated post-2005 as befits this ‘most significant revision in its history’) by chapter, a highly readable – therefore pedagogic? – style, and covers all the basics, from evolution, taxonomic overview of Kingdom Plantae (plus bacteria, archaea, viruses, fungi and algae), ultrastructure, anatomy, physiology and biochemistry, ecology (although those latter two chapters are now only available online), and even plant–people relationships (both as a separate 22-page chapter and as 15 short essays throughout the book's approx. 900 pages). Along with the extensive updating, Peter Raven's name has disappeared from the listing of authors. It is not clear to me why this has happened, but this 8th edition is dedicated to the much-lauded gentleman (a Time magazine ‘Hero for the Planet’; http://en.wikipedia.org/wiki/Peter_H._Raven) and who is now honoured in BoP's updated title, Raven Biology of Plants. And BoP retains its distinctive impressionistic cover – van Gogh's 1890 ‘Field of Poppies’ this time – which makes it stand out from the other books on the shelf! 
 
Does such a wonderful book have any competitors? Yes, there is a big, competitive market for undergraduate textbooks and plant biology is no exception. However, the textbook closest in style and coverage to BoP – that I know of – is the approx. 700-page tome Mauseth's Botany (2014), now in its 5th edition. I like ‘Mauseth’ (and it's not just because it's entitled botany!), but tend to turn to BoP first and supplement information from that source with material from other texts – such as Mauseth's. And you will need to supplement BoP with other sources. If you want more on the plant physiology side of things, then you will probably need the likes of specialist texts such as Taiz and Zeiger (2010). If you are after more of the molecular biology dimension, then Smith et al. (2010) or Jones et al. (2013) will help. To delve deeper into the structural–developmental side of plants, texts like Beck (2010) will be needed. For more on those all-important plants-and-people aspects of botany, then invaluable are Levetin and McMahon (2012) and Mauseth (2013), etc. The point is not that you don't need any other text than BoP, because you do!, but BoP is an excellent starting point for the basics of plant biology. Simply ‘mix-and-match’ BoP with your favourite, more specialist other texts to get the desired final outcome as suits your particular audience. 
 
So, in concluison, I don't think you can beat Raven Biology of Plants as a great all-round, comprehensive introduction to botany (oh, alright then! plant biology). 
 
An aside: the above comments refer to the so-called International Edition – ‘for use outside the USA and Canada’ – of BoP, 8th edition. I've often wondered what may be different in this edition compared to the USA one, and scrutinising Amazon's UK site I think I may have found the answer. The non-International Edition is shown retailing at about £120, but a reviewer (http://amzn.to/1jxOoOa) says that both editions have the same content. So, maybe the International Edition should be renamed the ‘Austerity’ Edition. In any event, it is nice to know that the Americans are helping out the cash-strapped botany students of Europe and non-USA/Canada!

title: CELLULAR BASIS FOR GROWTH AND TISSUE DIFFERENTIATION PATTERNS IN LINUM USITATISSIMUM (LINACEAE) STEMS: THE STEM UNIT
abstract: The stem unit is defined as the smallest portion of a stem that can duplicate the stem in toto through regular rotations and dilations over successive plastochrons. In stems exhibiting k(m, n) contact parastichy phyllotaxis, the stem unit is delimited vertically and tangentially by the boundaries of four successive leaf primordia along the m-, n-, and (m + n)parastichies and radially by these boundaries extended to the centroid of the stem. With the stem unit concept, node refers only to the region of actual leaf insertion, rather than the entire transverse level of insertion. Many of the conflicting and complicating aspects of the traditional node-internode subdivisions of stems are demonstrated, and the utility of the stem unit in circumventing these is illustrated. The stem unit is proposed as a more useful analytic subunit of the stem with which to examine stem growth and tissue differentiation processes than the more traditional node-internode subdivisions of stems. We know that both stem and root axes arise through expansion and differentiation of cells that are initially derived from meristematic cells comprising their terminal apical meristems. The kinematics of cellular activity with

title: Atlas of Woody Plant Stems: Evolution, Structure, and Environmental Modifications
abstract: Introduction1 1 The Evolution of Plant Stems in the Earth's History The Landscape in the Paleozoic Plant Body of Vascular Plants The Evolution of a Stabilizaton System The Contemporary Fossil Psilotum Nudum? Diversification of Plants Containing Tracheids The Lycopods The Horsetails The Fossil and Living Ferns Contemporary Ferns Trees Grow Taller and Bigger Successful Seed Plants with Naked Seeds Ginkgos and Cycads Gnetophytes (Ephedra, Gnetum and Welwitschia) The Most Successful Seed Plants with Naked Seeds: Conifers Successful Plants with Seeds Enclosed in a Carpel: Angiospermae 2 The Structure of the Plant Body Life Forms in Different Vegetation Zones Principal Growth Forms Principal Construction of Roots and Shoots Principal Construction of the Xylem and Phloem Cell Types, Cell Walls and Cell Contents 3 Secondary Growth: Advantages and Risks Primary and Secondary Growth Principle Structure of Plants with Secondary Growth Physiological and Ontogenetic Ageing The Risks of Water Transport: Stabilized and Permeable Cell Walls The Risks of Stem Thickening: Dilatation and Phellem Formation The Risks of Over-Production: Programmed Cell Death The Risks of Instability: Eccentricity Reaction Wood Formation of Lignin and Thick Cell Walls Internal Optimization The Risk of Decomposition: Natural Boundaries and Protection Systems Defence Barriers around Wounds The Risk of Shedding Plant Parts: Abscission 4 Modification of the Stem Structure The Primary Stage of Growth: The Construction of Vascular Bundles TheArrangement of Vascular Bundles in Mosses, Lycopods and Ferns The Arrangement of Vascular Bundles in Conifer and Dicotyledonous Plant Shoots The Secondary Stage of Growth: Conifer  The Xylem of Dicotyledonous Angiosperms The Primary and Secondary Stages of Growth of Monocotyledons: Macroscopic View Microscopic View The Secondary Stage of Growth: Conifer Phloem The Phloem of Dicotyledonous Angiosperms Cambial Growth Variants and Successive Cambia The Third Stage of Growth: The Periderm 5 Modification of the Xylem within a Plant Modification of the Xylem within a Plant Conifer: Root, Twig and Stem Deciduous Tree: Root, Twig and Stem From Root to Stem Structure Modification by Aging: Changing Growth Forms Changing Growth and Leaf Forms Changing Wood Anatomical Structures Change of Phloem and Periderm Structures 6 Modification of the Xylem and Phloem by Ecological Factors Intra-Annual Density Fluctuations, Phenolic and Crystal Deposits Intra-Annual Cell Collapse, Callous Tissue and Ducts Interannual Variation of Latewood Zones Long Term Variations: Sudden Growth Changes Inter- and Intra-Annual Variations of the Phloem 7 Modification of Organs Modification of Shoots: Long and Short Shoots Shedding Needles, Male and Female Flowers Thorns and Spines Vertical, Horizontal and Drooping Twigs Latent and Adventitious Shoots The Lateral Modification of Stems 8 Anatomical Plasticity Wood Structural Variability In Different Families In Different Growth Forms Under Different Site Conditions Modification Caused by Different Shoot and Root Function

title: Plant fibres: Botany, chemistry and processing for industrial use
abstract: Fibres from plant sources have been used by man for many generations and there is increasing interest in the potential use of such fibres from non-tree sources for various applications. This review brings together most of the relevant literature on the botany, chemistry and processing. The different cell types are explained and those which produce fibres are highlighted in conjunction with the actual plants involved. The chemistry of the plant cell wall is addressed with special consideration to the components of fibre cell walls and the biosynthesis, where known, is explained. Finally, the various methods for processing fibres into valuable industrial raw materials are detailed along with some prospective new technologies.

title: THE STRUCTURE AND DEVELOPMENT OF THE CELL WALL IN PLANTS I. BAST FIBERS OF BOEHMERIA AND LINUM
abstract: It is generally admitted that the bast fibers of Boehmeria nivea are among the longest in the higher plants, but there is considerable difference of opinion concerning the maximum length which they may attain. Hassack and Puric, as reported by Wiesner,' found fibers as long as 580 mm. and 520 mm. respectively, but Wiesner concluded that such "fibers" are composed of several cells. According to him, the longest single fibers are from 120-I50 mm. Most investigators in studying the size of bast fibers have utilized dried material which has been subjected to various commercial treatments. In material of this character, it is difficult to determine with certainty whether an isolated fiber is a single cell or a combination of several cells. The difficulty may be overcome, however, by macerating the freshly cut stems of living plants. The writer has obtained very satisfactory preparations by the following procedure. A flask is fastened to the lower end of a long glass tube, and an entire stem is inserted into this elongated, upright receptacle. The flask and the glass tube are filled with sufficient 5-percent solution of KOH to cover the stem. The base of the flask is placed in a water bath which heats and produces a circulation of the macerating fluid. By this arrangement it is possible to accomplish the maceration with very little injury to the fibers. Only a small amount of macerating fluid is required, and this may be changed from time to time. In order to insure an even maceration, the stem should not come In contact at any point with the sides of the glass tube. When the macerating treatment is completed, the fibers are isolated in a large, shallow pan of water. In so doing, it is essential that the parallel arrangement of the fibers be disturbed as little as possible. The isolated fibers are floated over strips of window glass which are coated with fixative. Twisting and buckling of the fibers is minimized by slowly raising one end of each glass strip, while preventing the fibers from drifting laterally. After the fibers are firmly attached to the glass, they are stained, dehydrated, dried, and covered with balsam. The object of the drying is to allow the lumina to become filled with air, which facilitates the task of

title: A procedure for identifying textile bast fibres using microscopy: flax, nettle/ramie, hemp and jute.
abstract: Identifying and distinguishing between natural textile fibres is an important task in both archaeology and criminology. Wool, silk and cotton fibres can readily be distinguished from the textile bast fibres flax, nettle/ramie, hemp and jute. Distinguishing between the bast fibres is, however, not easily done and methods based on surface characteristics, chemical composition and cross section size and shape are not conclusive. A conclusive method based on X-ray microdiffraction exists, but as the method requires the use of a synchrotron it is not readily available. In this paper we present a simple procedure for identifying the above mentioned textile bast fibres. The procedure is based on measuring the fibrillar orientation with polarised light microscopy and detecting the presence of calcium oxalate crystals (CaC2O4) in association with the fibres. To demonstrate the procedure, a series of fibre samples of flax, nettle, ramie, hemp and jute were investigated. The results are presented here. An advantage of the procedure is that only a small amount of fibre material is needed.

title: Secondary cell-wall assembly in flax phloem fibres: role of galactans
abstract: Non-lignified fibre cells (named gelatinous fibres) are present in tension wood and the stems of fibre crops (such as flax and hemp). These cells develop a very thick S2 layer within the secondary cell wall, which is characterised by (1) cellulose microfibrils largely parallel to the longitudinal axis of the cell, and (2) a high proportion of galactose-containing polymers among the non-cellulosic polysaccharides. In this review, we focus on the role of these polymers in the assembly of gelatinous fibres of flax. At the different stages of fibre development, we analyse in detail data based on sugar composition, linkages of pectic polymers, and immunolocalisation of the β-(1→4)-galactans. These data indicate that high molecular-mass gelatinous galactans accumulate in specialised Golgi-derived vesicles during fibre cell-wall thickening. They consist of RG-I-like polymers with side chains of β-(1→4)-linked galactose. Most of them are short, but there are also long chains containing up to 28 galactosyl residues. At fibre maturity, two types of cross-linked galactans are identified, a C–L structure that resembles the part of soluble galactan with long side chains and a C–S structure with short chains. Different possibilities for soluble galactan to give rise to C–L and C–S are analysed. In addition, we discuss the prospect for the soluble galactan in preventing the newly formed cellulose chains from completing immediate crystallisation. This leads to a hypothesis that firstly the secretion of soluble galactans plays a role in the axial orientation of cellulose microfibrils, and secondly the remodelling and cross-linking of pectic galactans are linked to the dehydration and the assembly of S2 layer.

title: Phloem fibres as motors of gravitropic behaviour of flax plants: level of transcriptome.
abstract: Restoration of stem vertical position after plant inclination is a widely spread version of plant orientation in accordance with gravity vector direction. Gravitropic behaviour of flax plants involves the formation of curvature in stem region that has ceased elongation long in advance of stem inclination. The important participants of such behaviour are phloem fibres with constitutively formed tertiary cell wall (G-layer). We performed the large-scale transcriptome profiling of phloem fibres isolated from pulling and opposite sides of gravitropic curvature and compared with control plant fibres. Significant changes in transcript abundance take place for genes encoding proteins of several ion channels, transcription factors and other regulating elements. The largest number of upregulated genes belonged to the cell wall category; many of those were specifically upregulated in fibres of pulling stem side. The obtained data permit to suggest the mechanism of fibre participation in gravitropic reaction that involves the increase of turgor pressure and the rearrangements of cell wall structure in order to improve contractile properties, and to identify the regulatory elements that operate specifically in the fibres of the pulling stem side making gelatinous phloem fibres an important element of gravitropic response in herbaceous plants.

title: Identification of Vegetable Fibres
abstract: This book should be of interest to those concerned with forensic science, conservationists in art and archaeology, textile and paper technologists and botanists.

title: Exploring the mechanical performance and in-planta architecture of secondary hemp fibres
abstract: Peak-Force Quantitative Nano-Mechanical property mapping (PF-QNM) and Micro Tomography were applied to explore the architecture and nano-mechanical properties of hemp secondary fibres cell walls. After a comparative morphological analysis of both primary and secondary fibres, secondary bundles structure and mechanical properties were investigated. As a first, it was showed that, in spite of important morphological differences, secondary fibres stiffness was the same that primary fibres one; moreover, innovative tomographic images gave an inedited representation of secondary bundles confirming the intrusive development of secondary hemp fibres.

title: Intrusive growth of flax phloem fibers is of intercalary type
abstract: Flax (Linum usitatissimum L.) phloem fibers elongate considerably during their development and intrude between existing cells. We questioned whether fiber elongation is caused by cell tip growth or intercalary growth. Cells with tip growth are characterized by having two specific zones of cytoplasm in the cell tip, one with vesicles and no large organelles at the very tip and one with various organelles amongst others longitudinally arranged cortical microtubules in the subapex. Such zones were not observed in elongating flax fibers. Instead, organelles moved into the very tip region, and cortical microtubules showed transversal and helical configurations as known for cells growing in intercalary way. In addition, pulse-chase experiments with Calcofluor White resulted in a spotted fluorescence in the cell wall all over the length of the fiber. Therefore, it is concluded that fiber elongation is not achieved by tip growth but by intercalary growth. The intrusively growing fiber is a coenocytic cell that has no plasmodesmata, making the fibers a symplastically isolated domain within the stem.

title: Microarray analysis of flax (Linum usitatissimum L.) stems identifies transcripts enriched in fibre-bearing phloem tissues
abstract: To better understand the molecular processes associated with the development of the unusually long (>30 mm) and strong bast fibre cells within the phloem of flax stems, we conducted a gene discovery experiment to identify transcripts enriched in fibre-bearing tissues, with the intention that these transcripts would serve as future targets for crop improvement and research in phloem development and cell wall deposition. We produced a library of 9,600 cDNA clones from the peels of flax stems, and selected tissue-specific cDNAs for sequencing based on two series of microarray experiments. In the first microarray series, we compared transcript abundance in stem-peels and leaves, and identified stem-enriched transcripts putatively involved in the processes of polysaccharide and cell wall metabolism. In the second microarray series, we compared gene expression in three segments of the vertical stem axis, which constituted a developmental series for phloem fibres and other cell types. The expression of specific LTP and AGP transcripts was particularly well-correlated with stem segments during either the elongation phase or cell-wall thickening phase of phloem fibre development, and the phloem-specific enrichment of these transcripts was confirmed by qRT-PCR. Transcripts representing multiple, distinct chitinases, β-galactosidases, arabinogalactan proteins (AGP), and lipid transfer proteins (LTPs) were among the interesting transcripts enriched in specific stages of the developing stem. Considered together, the results of our analyses suggest similarity between the molecular mechanisms underlying phloem fibre development and the gelatinous fibres of tension wood in trees.

title: Intrusive growth of sclerenchyma fibers
abstract: Intrusive growth is a type of cell elongation when the rate of its longitudinal growth is higher than that of surrounding cells; therefore, these cells intrude between the neighboring cells penetrating the middle lamella. The review considers the classical example of intrusive growth, e.g., elongation of sclerenchyma fibers when the cells achieve the length of several centimeters. We sum the published results of investigations of plant fiber intrusive growth and present some features of intrusive growth characterized by the authors for flax (Linum usitatissimum L.) and hemp (Cannabis sativa L.) fibers. The following characteristics of intrusive growth are considered: its rate and duration, relationship with the growth rate of surrounding cells, the type of cell elongation, peculiarities of the fiber primary cell wall structure, fibers as multinucleate cells, and also the control of intrusive growth. Genes, which expression is sharply reduced at suppression of intrusive growth, are also considered. Arguments for separation of cell elongation and secondary cell wall formation in phloem fibers and also data indicating diffuse type of cell enlargement during intrusive growth are presented.

title: Direct Insights on Flax Fiber Structure by Focused Ion Beam Microscopy
abstract: In this article, it is shown that focused ion beam (FIB) systems can be used to study the inner structure of flax fibers, the use of which as a reinforcing material in polymer composites still draws much interest from multiple disciplines. This technique requires none of the specific preparations necessary for scanning electron microscopy or transmission electron microscopy studies. Irradiation experiments performed on FIB prepared cross sections with very low Ga+ ion beam currents revealed the softer material components of fibers. Thus, it confirmed the presence of pectin-rich layers at the interfaces between the fibers of a bundle, but also allowed the precise localization of such layers within the secondary cell wall. Furthermore, it suggested new insights on the transition modes between the sublayers of the secondary cell wall.

title: Flax fibers: assessing the non-cellulosic polysaccharides and an approach to supramolecular design of the cell wall
abstract: Due to their particular tensile properties and composition, flax cellulosic fibres are widely used in various applications and are important in the stem architecture, as a source of mechanical support. Here, we have examined how various chemical extractions of cell-wall polysaccharides might improve our understanding of the structure and composition of these fibres. A set of chemical extractions, which had previously been independently studied on fibres of different origins and by different laboratories, was run on the same batch of technical fibres, variety Eden, and the released non-cellulosic polysaccharides were analyzed in terms of sugar composition and size exclusion chromatography. No single-step protocol was able to extract all the non-cellulosic polysaccharides estimated to be in the range of 130–140 mg per g of dry fibres. The major polymers consisted of rhamnogalacturonan and glucomannan, while the minor ones were xyloglucan and xylan. Several types of stepwise extractions helped to elucidate the subfractions of each polymer that are differently retained within cell wall. From our data, we have pointed out a new model which might help to approach the supramolecular design of the flax cellulosic fibres and, afterwards, the relationships between their chemical composition and their mechanical properties.

title: Immunocytochemical characterization of tension wood: Gelatinous fibers contain more than just cellulose.
abstract: Gelatinous fibers (G-fibers) are the active component of tension wood. G-fibers are unlike traditional fiber cells in that they possess a thick, nonlignified gelatinous layer (G-layer) internal to the normal secondary cell wall layers. For the past several decades, the G-layer has generally been presumed to be composed nearly entirely of crystalline cellulose, although several reports have appeared that disagreed with this hypothesis. In this report, immunocytochemical techniques were used to investigate the polysaccharide composition of G-fibers in sweetgum (Liquidambar styraciflua; Hamamelidaceae) and hackberry (Celtis occidentalis; Ulmaceae) tension wood. Surprisingly, a number of antibodies that recognize arabinogalactan proteins and RG I-type pectin molecules bound to the G-layer. Because AGPs and pectic mucilages are found in other plant tissues where swelling reactions occur, we propose that these polymers may be the source of the contractile forces that act on the cellulose microfibrils to provide the tension force necessary to bend the tree trunk.

title: Development of gravitropic response: unusual behavior of flax phloem G-fibers
abstract: The major mechanism of gravitropism that is discussed for herbal plants is based on the nonuniform elongation of cells located on the opposite stem sides, occurring in the growing zone of an organ. However, gravitropic response of flax (Linum usitatissimum L.) is well-pronounced in the lower half of developing stem, which has ceased elongation long in advance of plant inclination. We have analyzed the stem curvature region by various approaches of microscopy and found the undescribed earlier significant modifications in primary phloem fibers that have constitutively developed G-layer. In fibers on the pulling stem side, cell portions were widened with formation of “bottlenecks” between them, leading to the “sausage-like” shape of a cell. Lumen diameter in fiber widening increased, while cell wall thickness decreased. Callose was deposited in proximity to bottlenecks and sometimes totally occluded their lumen. Structure of fiber cell wall changed considerably, with formation of breaks between G- and S-layers. Thick fibrillar structures that were revealed in fiber cell wall by light microscopy got oblique orientation instead of parallel to the fiber axis one in control plants. The described changes occurred at various combinations of gravitational and mechanical stimuli. Thus, phloem fibers with constitutively formed gelatinous cell wall, located in nonelongating parts of herbal plant, are involved in gravitropism and may become an important element in general understanding of the gravity effects on plants. We suggest flax phloem fibers as the model system to study the mechanism of plant position correction, including signal perception and transduction.

title: The fine structure of fibers and crystalline polymers. III. Interpretation of the mechanical properties of fibers
abstract: The mechanics of extension of plant fibers is considered in terms of a spiral arrangement of crystalline fibrils embedded in a noncrystalline matrix. Deformation may take place either by stretching of the fibrils or by extension such as that of a spiral spring. In the latter, the major resistance comes from the reduction in volume. The extension mechanism predominates for low spiral angles; the spring mechanism, for high spiral angles. There is reasonable agreement between the theoretical expressions and experimental results. The application of similar ideas to other types of fiber structure is considered.

title: Investigation of the Mechanical Properties of Flax Cell Walls during Plant Development: The Relation between Performance and Cell Wall Structure
abstract: The development of flax (Linum usitatissimum L.) fibers was studied to obtain better insight on the progression of their high mechanical performances during plant growth. Fibers at two steps of plant development were studied, namely the end of the fast growth period and at plant maturity, each time at three plant heights. The indentation modulus of the fiber cell wall was characterized by atomic force microscopy (AFM) using peak-force quantitative nano-mechanical property mapping (PF-QNM). Changes in the cell wall modulus with the cell wall thickening were highlighted. For growing plants, fibers from top and middle heights show a loose inner Gn layer with a lower indentation modulus than mature fibers, which exhibit thickened homogeneous cell walls made only of a G layer. The influence of these changes in the fiber cell wall on the mechanical performances of extracted elementary fibers was also emphasized by tensile tests. In addition, Raman spectra were recorded on samples from both growing and mature plants. The results suggest that, for the fiber cell wall, the cellulose contribution increases with fiber maturity, leading to a greater cell wall modulus of flax fibers.

title: Occurrence of cell-specific galactan is coinciding with bast fiber developmental transition in flax
abstract: Bast fiber peels of developing flax (Linum usitatissimum L.) stem contain tissue-specific soluble (1→4)-β-galactan. The occurrence and localization of this polymer have been investigated at various stages of bast fiber development. Tissue-specific galactan (molecular mass >2000 kDa) emerged right below the snap point—the manually identified spot on the stem, above which the fiber cells elongate, while below no more elongation occurs, but intensive secondary cell wall thickening takes place. In the course of plant development the amount of tissue-specific galactan gradually declined and in mature plants the polymer disappeared from the fraction, being either degraded or fixed within the cell wall. The immunolocalization of (1→4)-β-galactans with LM5 antibody revealed that in flax stem these polymers were present only in bast fiber cells. Two layers were well pronounced within the secondary cell wall, the density of gold particles in the inner layer was 5.2±1.5 times higher than in the outer layer. To distinguish soluble galactan from other (1→4)-β-galactans, the stem sections were treated with buffer, which elutes buffer-soluble galactan. The soluble high molecular mass (1→4)-β-galactan is a bast fiber cell-specific polymer, emerging at the transition from cell elongation to cell wall thickening. It is localized in the inner portion of the secondary cell wall and is modified or degraded in the course of further plant development. This polymer belongs to the rarely observed plant cell wall polysaccharides, which only occurs at one specific stage of cell development, suggesting that it could play a prominent role in cellulose deposition and secondary cell wall formation in flax fibers.

title: Building flax fibres: more than one brick in the walls
abstract: The objective of the review is to provide fundamental knowledge on the chemical composition and structural characteristics of flax fibres. These are long and multinucleate cells without septum or partition (average length 2–5 cm) and have a secondary wall of very large thickness (5–15 μm). Fibres are gathered in bundles of one to three dozen cells that encircle the vascular cylinder. The bundle cohesion is insured by pectins, accumulating in the primary wall and cell junctions. In contrast, lignin, which is present in very low amount, does not seem to play a major role in bundle cohesion. At maturity, secondary wall is characterised by (i) a high level of cellulose with microfibrils locked into an almost axial direction and (ii) 5–15% non-cellulosic polysaccharides (NCPs). The chemical composition of NCPs depends on growth stage, indicating important cell wall remodelling, fibre position and variety. Despite the large disparity of the results reported in the literature, galactose appears to be the predominant sugar of NCPs, and β-1-4-galactan together with rhamnogalacturonan of type I (RG-I) and polygalacturonic acid (PGA) become, with fibre maturity, the most abundant tightly bound NCPs. Glycine-rich proteins (GRPs) and arabinogalactan-proteins (AGPs), also present in flax fibres, are both characterised by appreciable levels of glycine and acidic amino acid and are deficient in hydroxyproline, and may contribute to the cross-linking of pectins. (Galacto)glucomanans/glucans rather than xylans consist of cross-linking polymers in fibre secondary wall. A model is proposed where cellulose microfibrils, tethered by cross-linking (galacto)glucomanans/glucans, are embedded in a pectic matrix.

title: Elementary flax fibre tensile properties: Correlation between stress–strain behaviour and fibre composition
abstract: Flax fibres represent an eco-friendly alternative to glass fibres in composite materials. Natural fibres do not have a unique standard response to tensile testing. To increase understanding of the response to tensile testing, six batches of flax fibres ( Linum usitatissimum ) were selected for their differences in tensile properties: four batches consisted of Marylin-variety cultures grown in the same area but in different years, and two were reference-samples from Oliver and Hermes varieties. Their tensile values were either moderate ( E  ≈ 45–55 GPa, σ  ≈ 800–1000 MPa) or high ( E  > 55 GPa, σ  > 1000 MPa). Three major types of stress–strain behaviour were observed, but in different proportions in each sample. The first one consisted of a linear tensile behaviour; the second one was composed of two linear distinct sections, and the third one displayed a non-linear section at the beginning of the loading stage up to a threshold point, followed by a section where the tangent modulus increased up to failure. The samples exhibiting a large proportion of the third type of behaviour were characterised by high tensile properties. The extent of the non-linear section highly depended on the variety. Within the Marylin variety, the tensile properties were higher when the non-linear section was smaller. Considering the fibre as a composite per se , reinforced by cellulose microfibrils coated with hemicelluloses embedded in a matrix of incrusting pectins, we found some correlation between tensile behaviours and the cell-wall composition that highlighted the importance of the hemicelluloses and hemicelluloses/pectins ratio.

title: Development of Cellulosic Secondary Walls in Flax Fibers Requires β-Galactosidase1[C][W][OA]
abstract: Bast (phloem) fibers, tension wood fibers, and other cells with gelatinous-type secondary walls are rich in crystalline cellulose. In developing bast fibers of flax (Linum usitatissimum), a galactan-enriched matrix (Gn-layer) is gradually modified into a mature cellulosic gelatinous-layer (G-layer), which ultimately comprises most of the secondary cell wall. Previous studies have correlated this maturation process with expression of a putative β-galactosidase. Here, we demonstrate that β-galactosidase activity is in fact necessary for the dynamic remodeling of polysaccharides that occurs during normal secondary wall development in flax fibers. We found that developing stems of transgenic (LuBGAL-RNAi) flax with reduced β-galactosidase activity had lower concentrations of free Gal and had significant reductions in the thickness of mature cellulosic G-layers compared with controls. Conversely, Gn-layers, labeled intensively by the galactan-specific LM5 antibody, were greatly expanded in LuBGAL-RNAi transgenic plants. Gross morphology and stem anatomy, including the thickness of bast fiber walls, were otherwise unaffected by silencing of β-galactosidase transcripts. These results demonstrate a specific requirement for β-galactosidase in hydrolysis of galactans during formation of cellulosic G-layers. Transgenic lines with reduced β-galactosidase activity also had biochemical and spectroscopic properties consistent with a reduction in cellulose crystallinity. We further demonstrated that the tensile strength of normal flax stems is dependent on β-galactosidase-mediated development of the phloem fiber G-layer. Thus, the mechanical strength that typifies flax stems is dependent on a thick, cellulosic G-layer, which itself depends on β-galactosidase activity within the precursor Gn-layer. These observations demonstrate a novel role for matrix polysaccharides in cellulose deposition; the relevance of these observations to the development of cell walls in other species is also discussed.

title: Plant Biomechanics: An Engineering Approach to Plant Form and Function
abstract: Subject classification:- Earth Sciences: Paleontology Biological Sciences: Ecology Biological Sciences: Botany Biological Sciences: Physiology, Biomechanics, and Morpholog.

title: Interspecific allometries of critical buckling height and actual plant height
abstract: Size-dependent variations in the critical buckling height Hcrit and actual height H of plants were determined for a total of 1 1 1 species with self-supporting stems ranging in diameter between 0.03 cm c D c 3.0 m. For each species, experimentally determined values for the physical properties of stems (Young's elastic modulus and bulk tissue density) were used to compute Hcrit. For small species (D < 3 cm), empirically determined critical buckling loads were used to compute Hcrit by means of the Elastica equation and the more traditionally employed Greenhill formula; for larger species (D 2 3 cm), Greenhill's formula was used exclusively to estimate Hcrit. Within most of the size-range examined, the predicted values of Hcrit from the Elastica equation and Greenhill's formula were statistically indistinguishable. Regression analyses showed that the interspecific allometry of Hcrit parallels that of H such that the safety factor against the elastic mechanical failure of stems (i.e., Hcrit/H) under their own biomass was roughly constant. Since the safety factor against elastic buckling is independent of plant size, a general allometric "rule," Hcrit/H ; 4, appears to govern the evolution of plant size.

title: Understanding the lodging stability of green flax stems; The importance of morphology and fibre stiffness
abstract: Flax fibres (Linum usitatissimum) with good mechanical properties are required to reinforce polymers. Usually, their characterisation is made on retted and scutched fibres. This work provides a new and original method to both determine the stiffness of green fibres con- tained inside the plant and to estimate the crop lodging stability. We studied two recent flax varieties (Eden and Terre de Lin (TDL) 25) with a distinct lodging resistance (respectively high and low). Both varieties, grown under the same conditions, exhibit a similar fibre yield. The analysis conducted is based on the correlation between the bending stiffness of the stems, the distribution of fibres in a cross section and the properties of elementary flax fibres. The results of the mechanical characterisation indicate that the Eden variety has a superiority concerning fibre stiffness (68 GPa versus 55 GPa). The analysis of the bending stiffness of a dried plant at different localisations along the stem and of its fibre distribution in the corresponding cross section allowed us to estimate the fibres average modulus. Results obtained by this method were very close to the tensile tests values. The same procedure was used on green stems to approach the living state of the plant and to determine the Young's modulus of green fibres. The results highlighted a variation of fibre stiffness between the green state and the dried state (around þ25%). The results enabled the use of a simplified buckling model, which confirmed the superiority of the Eden variety in lodging resistance. Thus, the analysis of the mechanical properties of flax stems and their structure could be a selection criterion.

title: Stem and root characteristics associated with lodging resistance in four winter wheat cultivars
abstract: The effects of root and shoot characteristics on the lodging resistance of four cultivars of winter wheat were investigated by combining results from a field trial (set up at Manchester University's Experimental Grounds, Jodrell Bank, in mid-September 1991) with morphological and mechanical measurements on their stems and anchorage systems. Cultivars showed contrasting lodging resistance: Widgeon was most susceptible, followed by Galahad, Riband and Hereward which, alone, did not lodge. Lodging resistance was not related to the strength and stiffness of the stems, which were usually adequate to withstand the forces to which they were subjected. Most plants instead failed in their root system which rotated through the soil. Resistance was associated with short and light stems (and hence on the force applied to the plants by wind and gravity) and with high values of the anchorage strength of the root system (and hence on the force resisting lodging). Lodging occurred during grain filling when the ears were heaviest and when the soil was wet. The anchorage strength of a plant depended on two characteristics of the root system: the bending strength and the angle of spread of the basal coronal roots. Plants with stronger, more widely spread coronal roots produced larger soil cones during anchorage failure and resisted larger forces. Future breeding for lodging resistance, therefore, should continue to select for plants with shorter stems and with stiffer, more widely spread, coronal roots.

title: Structural development and stability of rice Oryza sativa L. var. Nerica 1.
abstract: The structural development of glasshouse-grown rice Oryza sativa L. var. Nerica 1 was studied in relation to its stability against lodging. The morphology and mechanical properties of both the stem and roots were examined from tillering, 4 weeks after transplantation up to maturity, together with plant weight distribution and anchorage strength. The "factors of safety" against root and stem failure were subsequently calculated throughout development. Rice plants showed similar morphology to wheat, although they possessed around twice as many tillers per plant and 10 times as many coronal roots. The mechanics of anchorage were also similar. The strength and rigidity of individual tillers increased throughout development as the plants grew taller and heavier and were around 15 times greater than in wheat. By contrast, individual root bending strength, the number of roots, and the anchorage strength levelled off earlier, and anchorage strength was only around twice that in wheat. Consequently, while the self-weight safety factor against stem failure was much higher than in wheat, increasing until late on in development from around 30 to 150, the self-weight safety factor against root anchorage failure was similar to wheat, decreasing from around 15 to 5. Consequently, plants subjected to anchorage tests always failed in their root system rather than their shoot system. The results suggest that, in the field, rice plants would be more likely to undergo root lodging than stem lodging, and that breeding efforts to reduce the incidence of lodging should act to strengthen the rather weak coronal roots.

title: Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth.
abstract: Advances in determination of polymer structure and in preservation of structure for electron microscopy provide the best view to date of how polysaccharides and structural proteins are organized into plant cell walls. The walls that form and partition dividing cells are modified chemically and structurally from the walls expanding to provide a cell with its functional form. In grasses, the chemical structure of the wall differs from that of all other flowering plant species that have been examined. Nevertheless, both types of wall must conform to the same physical laws. Cell expansion occurs via strictly regulated reorientation of each of the wall's components that first permits the wall to stretch in specific directions and then lock into final shape. This review integrates information on the chemical structure of individual polymers with data obtained from new techniques used to probe the arrangement of the polymers within the walls of individual cells. We provide structural models of two distinct types of walls in flowering plants consistent with the physical properties of the wall and its components.

title: Immunocytochemical characterization of early-developing flax fiber cell walls
abstract: SummaryThe deposition and formation of a thick secondary wall is a major event in the differentiation of flax (Linum usitatissimum) fibers. This wall is cellulose-rich; but it also contains significant amounts of other matrix polymers which are noncellulosic such as pectins. We have used immunocytochemical techniques with antibodies specific for various epitopes associated with either pectins or arabinogalactan proteins (AGPs) to investigate the distribution of these polymers within the walls of differentiating young fibers of 1- and 2-week-old plants. Our results show that different epitopes exhibit distinct distribution patterns within fiber walls. Unesterified pectins recognized by polygalacturonic acid-rhamnogalacturonan I (PGA/RG-I) antibodies and rhamnogalacturonan II recognized by anti-RG-II-borate complex antibodies are localized all over the secondary wall of fibers. PGA/RG-I epitopes, but not RG-II epitopes, are also present in the middle lamellae and cell junctions. In marked contrast, β-(1→4) galactans recognized by the LM5 monoclonal antibody and AGP epitopes recognized by anti-β-(1→6) galactan and LM2 antibodies are primarily located in the half of the secondary wall nearest the plasma membrane. LM2 epitopes, present in 1-week-old fibers, are undetectable later in development, suggesting a regulation of the expression of certain AGP epitopes. In addition, localization of cellulose with the cellobiohydrolase I-gold probe reveals distinct subdomains within the secondary walls of young fibers. These findings indicate that, in addition to cellulose, early-developing flax fibers synthesize and secrete different pectin and AGP molecules.

title: Microscopic Studies on Mature Flax Fibers Embedded in LR White
abstract: Flax fibers have been the subject of many biochemical studies, which revealed that cellulose and pectins are the major constituents of their walls. In contrast, little is known about the location of these polymers within the walls of mature fibers by microscopic methods. This has been technically hampered by the very thick secondary wall of fibers, resulting in inadequate tissue preservation unsuitable for immunogold microscopy. In this study, we adapted the basic chemical fixation, dehydration and infiltration methods to achieve a good preservation of the cell structures of mature fibers and reduced damage to antigens. We were able to apply postembedding immunocytochemical techniques to map the location of various pectic epitopes within the walls of mature fibers. Our immunolabeling data show that homogalacturonans were exclusively found in the middle lamellae and the cell junctions but were not detectable in the secondary wall. In contrast, rhamnogalacturonan I (RG I)-associated epitopes, as well as galactan and arabinan epitopes, were abundantly distributed over the secondary wall of mature fibers.

title: Tensional stress generation in gelatinous fibres: a review and possible mechanism based on cell-wall structure and composition.
abstract: Gelatinous fibres are specialized fibres, distinguished by the presence of an inner, gelatinous cell-wall layer. In recent years, they have attracted increasing interest since their walls have a desirable chemical composition (low lignin, low pentosan, and high cellulose contents) for applications such as saccharification and biofuel production, and they have interesting mechanical properties, being capable of generating high tensional stress. However, the unique character of gelatinous layer has not yet been widely recognized. The first part of this review presents a model of gelatinous-fibre organization and stresses the unique character of the gelatinous layer as a separate type of cell-wall layer, different from either primary or secondary wall layers. The second part discusses major current models of tensional stress generation by these fibres and presents a novel unifying model based on recent advances in knowledge of gelatinous wall structure. Understanding this mechanism could potentially lead to novel biomimetic developments in material sciences.

title: Relationships between micro-fibrillar angle, mechanical properties and biochemical composition of flax fibers
abstract: An elementary plant fiber could be assimilated to a laminate, mainly constituted of the secondary wall S2 layer, made of a few non-crystalline polysaccharides reinforced by cellulose fibrils organized in a helix, with a microfibrillar angle (MFA) around 10° relative to the longitudinal fiber axis. This paper investigates the relationships between the MFA, the mechanical properties and the biochemical composition of different varieties of flax. To conduct this study, tensile tests on elementary flax fibers, X-ray diffraction, and solvent extractions have been carried out. Within the different varieties of flax, Young's modulus was found to be negatively correlated with the MFA. The results showed that the ratio between hemicelluloses (matter extracted with alkali) and pectins (hydrolyzed with acids) is highly correlated with the tensile properties; concurrently, we showed the great influence of pectic acids on the fiber’ Young's modulus, and on the orientation of the microfibrils.

title: Cellulose microfibril angle in the cell wall of wood fibres
abstract: The term microfibril angle (MFA) in wood science refers to the angle between the direction of the helical windings of cellulose microfibrils in the secondary cell wall of fibres and tracheids and the long axis of cell. Technologically, it is usually applied to the orientation of cellulose microfibrils in the S2 layer that makes up the greatest proportion of the wall thickness, since it is this which most affects the physical properties of wood. This review describes the organisation of the cellulose component of the secondary wall of fibres and tracheids and the various methods that have been used for the measurement of MFA. It considers the variation of MFA within the tree and the biological reason for the large differences found between juvenile (or core) wood and mature (or outer) wood. The ability of the tree to vary MFA in response to environmental stress, particularly in reaction wood, is also described.

title: Specific type of secondary cell wall formed by plant fibers
abstract: The review sums data indicating that, in many plant fibers, the secondary cell wall contains so-called gelatinous layers of peculiar structure along with those of common (xylan) structure. Sometimes these gelatinous layers comprise the main bulk of the cell wall. Key characteristics of gelatinous cell wall are presented and compared with those of classic xylan-type cell wall. The process of gelatinous cell wall formation is considered in detail for flax phloem fibers; several characteristic features of this process were revealed: intense rearrangement of already deposited cell-wall layers, unusual dynamics of Golgi vesicles, the occurrence of the stage-specific polysaccharide with specific properties, high activity of β-galactosidase, and the presence of substantial amount of free galactose. Similarity and differences in the gelatinous cell wall formation in the fibers of various plant species are discussed.

title: Current status and future scenarios of hemp breeding
abstract: SummaryHemp is a multi-use crop, able to provide fiber, cellulose, seeds and seed oil, cannabinoid, and biomass. Integrating many agroindustrial chains, Cannabis is considered a crop model in which insights into specific metabolic pathways and biosynthetic processes are valuable for improvement of the plant for all sets of industrial derivatives. In this review the hemp breeding status is elucidated and many aspects are focused: (i) recovering, maintenance and characterization of genetic resources; (ii) widening of germplasm and genetic variability; (iii) marker-assisted selection and development of breeding programs; (iv) sexual differentiation; (v) monitoring of THC content. Modern hemp varieties for fiber and other specific end uses have been developed and new varieties are entering production. The scenario for the breeding advances in hemp relies on basic and applied research which provides insights to identify a strategy for the design of modified plants with enhanced performance. This is accounted by the dissection of traits into components and the modification of single steps of the related metabolic pathways. These advances are provided by genomic techniques and are able: (i) to identify key genes encoding enzymes and regulatory factors participating in cannabinoid, fiber and oil biosynthesis; (ii) to identify the mode of regulation of these genes; (iii) to characterize the function of the selected genes through higher, lower or specific expression incited by specific promoters. The identification of molecular markers for specific traits, gathered in a saturated linkage map, will have a remarkable impact on hemp breeding. The advances in basic and applied research make it possible to design methods for the identification of superior parents and cross combinations and the development of selection schemes that rely on less labour-intensive and time-consuming methods.

title: Investigation of the internal structure of hemp fibres using optical coherence tomography and Focused Ion Beam transverse cutting
abstract: The use of plant fibres in composite applications requires an efficient characterisation of their mechanical properties and thus an accurate description of their internal structure. The review of literature points out that there is still a lack of data on the organisation and structure of bast fibres. In this study, we propose to investigate the internal structure of hemp fibres using two experimental techniques: Focused Ion Beam (FIB) microscopy and optical coherence tomography (OCT). Results indicate that OCT, a non-destructive and non-invasive technique, is a powerful technique to quickly and easily describe the internal structure of fibres and also to discriminate single fibres from bundle of fibres. In this paper, we also show that among technical hemp fibres and for a same range of external diameters (of about 20–30 μm), two types of internal structures can be observed: (i) elementary fibres with a thick wall and a small lumen and (ii) bundle of small fibres with an external diameter of a few microns. According to data of literature, these two structures were identified as being respectively primary fibres and bundle of secondary fibres. This result is of great importance for the mechanical characterization of the bast hemp fibres. Indeed, this means that during the test campaigns, the batch of isolated fibres is undoubtedly composed of both single primary fibres and bundle of secondary fibres. It certainly participates to the high scattering in results.

title: A More Reliable Evaluation of Hemp THC Levels is Necessary and Possible
abstract: Most industrial crops that are cultivated within the 27 member states of the European Union (EU) are supported by agricultural subsidies. An official list of the hemp varieties that receive an agricultural subsidy in the EU is maintained by the EU Commission, and EU member states are expected to sample, analyze, and report delta-9-tetrahydrocannabinol (THC) values for eligible crops of each cultivated variety by the end of each year, according to EU Regulation No. 796/2004. Based on this information, additions to and deletions from this list are made early in the following year. The main criteria for being included on the EU list of subsidized hemp varieties seems to depend on two important factors: the variety be included in the EU Common Catalogue of recognized plant cultivars, and the variety, on average, must have less than 0.2% THC, according to the sampling and testing methodologies described in Annex I of EU Regulation No. 796/2004. By comparison, values for common drug-Cannabis typically range from 5–10% THC. The purpose of this article is to point out important features in the EU sampling protocols that favor monoecious fiber varieties from western Europe and disfavor dioecious oilseed varieties from eastern and northern Europe, in addition to other peculiar features. Also, potential systematic problems that exist within the current analytical protocol for analyzing THC are identified and discussed. Direct criticism is leveled at the ignorance and incompetence demonstrated by civil servants who are responsible for correctly understanding and implementing EU Regulation No. 796/2004. Suggestions for improvements in various aspects of reporting, sampling, and analytical methodologies are presented.

title: Current Status and Challenges of Rice Production in China
abstract: Rice production in China has more than tripled in the past five decades mainly due to increased grain yield rather than increased planting area. This increase has come from the development of high-yielding varieties and improved crop management practices such as nitrogen fertilization and irrigation. However, yield stagnation of rice has been observed in the past ten years in China. As its population rises, China will need to produce about 20% more rice by 2030 in order to meet its domestic needs if rice consumption per capita stays at the current level. This is not an easy task because several trends and problems in the Chinese rice production system constrain the sustainable increase in total rice production. Key trends include a decline in arable land, increasing water scarcity, global climate change, labor shortages, and increasing consumer demand for high-quality rice (which often comes from low-yielding varieties). The major problems confronting rice production in China are narrow genetic background, overuse of fertilizers and pesticides, breakdown of irrigation infrastructure, oversimplified crop management, and a weak extension system. Despite these challenges, good research strategies can drive increased rice production in China. These include the development of new rice varieties with high yield potential, improvement of resistances to major diseases and insects, and to major abiotic stresses such as drought and heat, and the establishment of integrated crop management. We believe that a sustainable increase in rice production is achievable in China with the development of new technology through rice research.

title: Genetic engineering and biotechnology of natural textile fiber plants
abstract: Since ancient times, fiber crops have been closely connected with everyday life of human beings and have been utilized for many basic purposes including food, clothing and housing. Although over 2000 different species of fibrous plants are known, the list of commercially important fiber plants is not long, encompassing cotton, flax, jute, hemp, kenaf and ramie. Hard, leaf or structural fibers are obtained from agaves, Manila hemp and Mauritius hemp. From seed and fruit fibers, cotton, kapok and coconut have found commercial application. The same fiber may be used for different purposes. Genetic engineering and biotechnology give opportunities to improve the yield and quality of fiber crops precisely and more efficiently as compared with traditional breeding methods. From commercially available biotech crops, cotton is one of the most popular transgenic crops constituting 49% of total cotton production.

title: Quantitative analysis of Linum usitatissimum crosses for dual-purpose traits
abstract: The commercial future of Linum usitatissimum is intrinsically linked to its cultivation as a dual-purpose crop for producing increased seed and fibre yields. The present study evaluates 36 F 1 crosses derived from nine linseed/flax accessions for their potential as dual-purpose cultivars and/or their suitability for extracting new recombinants producing high seed yield as well as increased fibre output. The quantitative analysis indicated that variation between the F 1 families is largely but not exclusively due to the additive and non-additive (dominance) effects of genes. Dominance is high for plant height (H1), height at maturity (HMT), number of branches (NBr) and seed weight (SdWt) while 100 seed weight (Wt100) displays no dominance at all. The repeatability estimates representing the heritability of each trait, vary from low (0.20) for number of branches (NBr) to high (0.71) for height at flowering time (HFT). The dual-purpose traits such as seed weight (SdWt) and straw weight (StWt) were only moderately inherited while flowering time (FT) and various heights were rather highly heritable. A moderate and positive correlation (r = 0.57) between StWt and SdWt, and a completely independent inheritance of Wt100 suggested that there are good chances of combining these traits into a single genotype. The phenotypic performance of the crosses also confirmed this trend and at least four crosses showed superior performance for both SdWt and StWt compared to their parental lines. All these crosses involved a linseed line (B3) as a common parent and the second parent was either another linseed line (A1 and A3) or a flax accession (K3 and L2); none of the flax x flax crosses showed good potential for seed yield. While all four crosses possess the potential to become highly productive, dual-purpose, hybrid varieties, the extraction of desirable inbred lines from them, however, may prove difficult because the superior performance of the hybrids seems largely due to strong unidirectional dominance and high SCA effects.

title: Research of technical crops (potato and flax) genetic resources in Lithuania.
abstract: The research of potato accessions preserved in Lithuanian potato gene bank genetic diversity research was carried out at the Voke branch of Lithuanian Institute of Agriculture in years 1990-2006. Research was provided with potato collection covering 200 varieties and hybrids from the main potato origin and growing regions and selection material bred in Lithuania. Potato varieties varied in accordance of morphologic, physiologic, immunologic and farming features in the different maturity groups and between groups. Using transgenic hybridization method and working with genetic material of local potato collection were selected potato varieties of Lithuanian origin. The key objective was to select the varieties immune to wart disease, cyst nematodes, with high resistance to other diseases, with excellent agronomic and cooking qualities, suitable for the processing industry. Over 1966-2006 years the collection of more than 350 flax breeding lines and varieties from different countries were investigated at the Upyte Research Station of the Lithuanian Institute of Agriculture. Therefore it is desirable for the new flax varieties to be highly adaptable, stabile yielding and high fiber quality under different growing conditions. The collection serves as a base while selecting flax varieties for hybridization. There have been chosen the varieties and breeding lines having the complex of qualities and positive characters. The varieties and breeding lines with positive characters were involved into the program of fiber flax breeding.

title: Varietal selection of flax over time: Evolution of plant architecture related to influence on the mechanical properties of fibers
abstract: The varietal selection of flax ( Linum Usitatissimum L.) has always focused on specific criteria fulfilling requirements of farmers and textile workers. Thus, the current development of composites using flax as reinforcement presents new challenges for flax breeders in terms of fiber quantities and quality. However, the impact of the varietal selection on the mechanical properties of resulting fibers is yet to be determined. In the present study, several architectural characteristics of flax stems are defined. Stem transverse sections from four varieties selected from the 1940s to 2011 are compared. Anatomical changes over time are highlighted. The most important ones involve the gap between fiber bundles and the amount of fibers which can be improved with the selection (from 7.8% to 13.4% of the tissue area per section). This trend coincides with the increase in biomass production over time expected from the selection work. Moreover, this study demonstrates that flax fibers preserve their good mechanical performances in spite of the anatomical differences. Thus, through varietal selection, it is possible to increase the biomass yield while preserving the excellent specific mechanical properties of flax fibers. Finally, flax fibers can compete with glass fibers to reinforce composite materials.

title: Impact of the seeding rate on flax stem stability and the mechanical properties of elementary fibres
abstract: Cultivation of flax fibres (Linum usitatissimun) for composite reinforcement must provide fibres with good mechanical properties, but also a high fibre yield and lodging stability in order to ensure a stable and satisfactory income for the farmer. This work proposes a study of the impact of the seeding rate on these key parameters. We studied the Aramis variety with 4 different seeding rates (1200, 1500, 1800 and 2500 seeds/m2). The results indicate the significant impact of the seeding rate on the stem’s morphological parameters; its increase induces a progressive decrease of the scutched fibre length and of the stem diameter. At the same time, the higher seeding rates obtained improved the scutched fibre’s yield (+11% between 1200 and 2500 seeds/m2) but, conversely, induced a drop in the elementary fibre’s tensile properties and in the flax stem’s lodging stability, mainly due to the large decrease in the stem’s diameter. This work shows that a compromise must be found to optimize the fibre yield, the mechanical performance and the plant’s stability; it underlines the relevance of using a conventional seeding rate, close to 1800 seeds/m2.

title: Inheritance of resistance to flax wilt (Fusarium oxysporum f.sp. lini Schlecht) in a doubled haploid population of Linum usitatissimum L.
abstract: The inheritance of resistance to fusarium wilt (Fusarium oxysporum f.sp. lini) was investigated in Linum usitatissimum as a first step towards gaining an understanding of the molecular genetics of the disease and developing a procedure for marker-assisted selection. A recombinant doubled haploid (DH) population was derived from the haploid component of polyembryonic F2 seeds originating from a cross between a wilt resistant, twinning Linola™ Linola is a registered trademark of CSIRO line CRZY8/RA91 and the wilt susceptible Australian flax cultivar Glenelg. The segregation of resistance was studied in 143 DH lines under glasshouse and field conditions. Most of the phenotypic variation was attributable to the segregation of two independent genes with additive effects. Minor resistance genes may have also contributed by modifying the resistance response. A glasshouse screening method of DH lines proved a reliable indicator of field resistance to fusarium wilt.

title: Inheritance of resistance to powdery mildew in flax
abstract: Powdery mildew, caused by Oidium lini, is an important disease of flax (Linum usitatissimum) in western Canada. Investigations on the genetics of resistance to powdery mildew in flax resulted in the identification of several resistant Canadian and introduced cultivars. A single dominant gene for resistance to powdery mildew, designated PM1, was identified in Canadian flax cultivars (‘AC Watson’, ‘AC McDuff’, and ‘AC Emerson’) and introduced flax cultivars (‘Atalante’ and ‘Linda’). In addition, two putative dominant genes for resistance to powdery mildew were identified in ‘Linda’.

title: Short Communication: Comparative effect of lodging on seed yield of flax and wheat
abstract: Vera, C. L., Duguid, S. D., Fox, S. L., Rashid, K. Y., Dribnenki, J. C. P. and Clarke, F. R. 2012.  Comparative effect of lodging on seed yield of flax and wheat. Can. . Lodging may limit crop productivity and hinder the normal process of harvesting crops. Results from 16 yr (1994–2009) of the Flax Co-operative test and from 29 yr (1981–2009) of the Central Bread Wheat Co-operative test, conducted annually for the evaluation of advanced breeding lines at various locations in the provinces of Manitoba, Saskatchewan and Alberta, Canada, were used to determine the effect of lodging on the seed yield of these two crop species. Seed yield data were regressed on corresponding lodging scores (1–9 scale) collected from field evaluations. Lodging was more frequently a problem in flax (Linum usitatissimum L.) than in wheat (Triticum aestivum L.), with average seed yield reductions of 32% and 16%, respectively, when lodging was most severe. Disease has been observed in asso...

title: Development of a Model of Lodging for Barley
abstract: Lodging in barley (Hordeum vulgare L.) can result either from buckling of any part of the stem (stem lodging) or failure of the root–soil anchorage system (root lodging). A framework for calculating the risk of stem lodging is developed which takes account of the shoot's height, ear area, natural frequency, weight, the flexural rigidity of the stem and changes in stem strength along its length. The model predicted that stem lodging in barley cultivars would occur half way up the stem, and stem lodging in wheat would occur close to the soil surface. These predictions are consistent with general observations of stem lodging in barley and wheat. The higher position of stem lodging in barley, compared with wheat, was caused by the greater flexibility of the barley stems and a more rapid reduction in stem strength up the stem. A sensitivity analysis showed that the stem diameter of the middle internodes had the greatest effect on the risk of stem lodging. Changes to ear area, drag coefficient, crop height, shoot natural frequency and the strength of the stem wall had a moderate influence. Measurements of anchorage strength in barley and wheat plants indicated that the mechanism of anchorage failure was the same for both species and that a model of root lodging developed for wheat could be successfully adapted for barley.

title: Ideotype design for lodging-resistant wheat
abstract: The plant characteristics required to make wheat lodging-proof for the least investment of biomass are calculated using a validated model of the lodging process and information about the dry matter costs of altering lodging-associated characters. The plant characteristics required to give a crop yielding 8 t ha−1 with 500 shoots m−2 and 200 plants m−2, a lodging return period of 25 years include a height of 0.7 m, a root plate spread of 57 mm, and for the bottom internode a wall width of 0.65 mm with a diameter/material strength combination ranging from a diameter of 5.86 mm with a material strength of 20 MPa to a diameter of 4.00 mm with a material strength of 50 MPa. It is estimated that this ideotype would require 7.9 t ha−1 of stem biomass and would have a harvest index of 0.42. Observations of a wide range of varieties grown using crop management to maximise lodging resistance without reducing yield potential showed that the root plate of the best variety was 7 mm less than the ideotype target, the stem character targets were achieved but not all in one variety, and the height target was achievable with the use of plant growth regulators. Plant breeders must therefore focus on selecting for a wider root plate and combining the appropriate stem strength characteristics.

title: An analysis of the problem of lodging with particular reference to wheat and barley
abstract: It has been shown that structural failure in small grain cereals occurs by buckling rather than by loss of anchorage. A theoretical study established the relationship between a lateral force applied to the head, and failure of the straw. Resistance to bending is determined by two factors, Young's modulus and outer diameter of the straw. These were determined in laboratory tests. The value of Young's modulus was affected by stage of maturity of the straw. Wind-tunnel experiments established a relationship between air velocity and deflexion of the head. An attempt was made to calculate the wind speed necessary to cause straw breakage in the field. The kinetic effect of raindrops was not a significant factor in lodging. Attention has been drawn to the possible importance of taper in the straw.

title: Controlling plant form through husbandry to minimise lodging in wheat
abstract: Plant characters which affect lodging in winter wheat ( Triticum aestivum L.) were investigated through husbandry-change experiments at ADAS Rosemaund near Hereford (UK) over three seasons (1994–1996). Treatments were sowing date (20 September to 1 November), seed rate (500 and 250 seeds m −2 ) and residual soil nitrogen (116–46 kg ha −1 in February), in all combinations with four spring treatments: none, one or two plant growth regulators (PGRs), or reduced and delayed applications of nitrogen. The separate and combined effects of all plant characters on lodging were estimated using a model to calculate the minimum wind speed at which a shoot’s leverage would exceed the strength of its stem base (stem lodging), and at which the leverage of all the shoots on a plant would exceed its anchorage strength (root lodging). Measurements in July showed that all plant characters were influenced by the husbandry treatments, most changes increasing the minimum wind speed at which the plant lodges. PGRs, reduced spring nitrogen and delayed sowing reduced shoot leverage by reducing the height at centre of gravity and increasing natural frequency. Reduced spring nitrogen also reduced ear area. Delayed sowing, low residual nitrogen and reduced spring nitrogen increased stem strength by increasing both stem diameter and wall width. Soils with low residual nitrogen also increased material strength (failure yield stress) of the stem wall. Reduced seed rate increased stem diameter but reduced material strength slightly. Reducing seed rate also increased anchorage by increasing the spread and depth of the root plate. However, low seed rates also increased shoot number per plant, which partially counteracted the root plate effect. The most robust plants grown in this study were calculated to require gust speeds of 26–28 m s −1 to cause stem and anchorage failure. It was estimated that wheat must withstand gusts of up to 40 m s −1 if it is to lodge only once every century. This study concludes that the best husbandry practices, which are compatible with high yields, could not achieve the structural specification to withstand such wind gusts. It is suggested that new genotypes are needed to achieve lodging-proof wheat crops, particularly to provide stronger basal internodes and a wider root plate per shoot.

title: Understanding and Reducing Lodging in Cereals
abstract: Improved lodging resistance has contributed significantly to the dramatic increase in cereal yields observed in many countries during recent decades. Several advances in understanding lodging have been made since the last major review of lodging in 1973. These include: (1) a more thorough quantification of the effects of lodging on grain yield and quality, (2) collaborative studies by biologists and engineers have elucidated the mechanisms of stem and anchorage failure and the way in which cereal shoots interact with the wind and rain, (3) the development of models of the lodging process and (4) explanations for how crop husbandry decisions affect lodging. This review collates the new understanding of lodging and attempts to set out cultural and genetic-based approaches for the continued reduction of lodging risk in high-yielding cereals. The review demonstrates that the prospects for continuing to reduce lodging risk through the selection of shorter genotypes may be limited because there appears to be a minimum crop height that is compatible with high yields. There does appear to be significant scope for increasing lodging resistance by strengthening the stem and the anchorage system by exploiting the wide genetic variation in these plant characters and through crop management decisions.

title: ON THE FLEXURE OF THIN CYLINDRICAL SHELLS AND OTHER SECTION
abstract: It is a generally appreciated deduction from St. Venant’s solution of the flexure problem that a beam in which the material is disposed at a distance from the neutral axis is superior to the solid section in economy of material. St. Yenant’s solution, however, suggests that this advantage increases without limit as the thickness of the material is reduced and the distance from the neutral axis is increased. It has, of course, been generally realised that this conclusion is not supported by ordinary engineering practice, and recent experience in the use of high tensile steels and problems of aircraft structure have emphasised the desirability of a further examination of the flexure problem. St. Venant’s solutions are obtained when the equations of equilibrium of an isotropic elastic solid are made linear by the neglect of terms of higher orders than the first: and by Kirchhoff’s theorem of determinancy these solutions may then be considered unique and stable. To attack problems of stability it is necessary, as is shown by R. V. Southwell in his ‘General Theory of Elastic Stability,’ to include some of the second order effects. It is, in fact, only when these become considerable that Kirchhoff’s theorem fails and instability becomes possible. By this general treatment various classes of instability are obtained or indicated, but the only ones susceptible to analysis or of practical interest (on account of the “elastic limit” which is a feature of all practical materials) are those in which at the moment of instability the strains are still small. Bryant has shown that this will only occur, as in the case of thin rods and shells, when one dimension of the body is small compared with others.

title: The influence of gravity and wind on land plant evolution.
abstract: Aspects of the engineering theory treating the elastic stability of vertical stems and cantilevered leaves supporting their own weight and additional wind-induced forces (drag) are reviewed in light of biomechanical studies of living and fossil terrestrial plant species. The maximum height to which arborescent species can grow before their stems elastically buckle under their own weight is estimated by means of the Euler-Greenhill formula which states that the critical buckling height scales as the 1/3 power of plant tissue-stiffness normalized with respect to tissue bulk density and as the 2/3 power of stem diameter. Data drawn from living plants indicate that progressively taller plant species employ stiffer and lighter-weight plant tissues as the principal stiffening agent in their vertical stems. The elastic stability of plants subjected to high lateral wind-loadings is governed by the drag torque (the product of the drag force and the height above ground at which this force is applied), which cannot exceed the gravitational bending moment (the product of the weight of aerial organs and the lever arm measured at the base of the plant). Data from living plants indicate that the largest arborescent plant species rely on massive trunks and broad, horizontally expansive root crowns to resist drag torques. The drag on the canopies of these plants is also reduced by highly flexible stems and leaves composed of tissues that twist and bend more easily than tissues used to stiffen older, more proximal stems. A brief review of the fossil record suggests that modifications in stem, leaf, and root morphology and anatomy capable of simultaneously coping with self-weight and wind-induced drag forces evolved by Devonian times, suggesting that natural selection acting on the elastic stability of sporophytes occurred early in the history of terrestrial plants.

title: INFLUENCE OF NEIGHBORS ON TREE FORM: EFFECTS OF LATERAL SHADE AND PREVENTION OF SWAY ON THE ALLOMETRY OF LIQUIDAMBAR STYRACIFLUA (SWEET GUM)
abstract: Liquidambar styraciflua (sweet gum) saplings were open grown (control), guy-wired to prevent wind-induced sway (constrained), or guy-wired within open-topped shade cloth cylinders to simulate shading by neighboring trees (shaded). Mechanical stability was assessed after 2 years of growth by field measurement of whole-tree flexibility and with the critical buckling height predictions of five allometrical models. Data from this experiment are supplemented with measurements of sweet gum trees growing in a 9-year-old pine plantation; individuals crowded but not overtopped by pines are compared with similar-aged trees growing in openings within the plantation. Changes in aboveground architecture were stimulated by both prevention of sway and lateral shade but the effect of the latter was most pronounced; shaded saplings approached or exceeded their calculated critical height and buckled under their own weight when the shade cloth cylinders were removed. Rates of aboveground biomass acquisition, total leaf area, wood density, and wood elastic moduli did not differ among the three treatments; changes in stem allometry accounted for most of the observed differences in tree stability. Sweet gum trees growing in a pine plantation responded similarly to neighbors; crowded trees had larger height: diameter ratios and more closely approached their calculated critical heights than did trees growing in the open. Sweet gum saplings growing in dense stands of similar-sized plants may surmount their neighbors by allocating relatively more wood to height growth than to girth increment.

title: How to determine sapling buckling risk with only a few measurements.
abstract: Tree buckling risk (actual height/critical buckling height) is an important biomechanical trait of plant growth strategies, and one that contributes to species coexistence. To estimate the diversity of this trait among wide samples, a method that minimizes damage to the plants is necessary. On the basis of the rarely used, complete version of Greenhill's model (1881, ), we precisely measured all the necessary parameters on a sample of 236 saplings of 16 species. Then, using sensitivity (variance) analysis, regressions between successive models for risk factors and species ranks and the use of these models on samples of self- and nonself-supporting saplings, we tested different degrees of simplification up to the most simple and widely used formula that assumes that the tree is a cylindrical homogeneous pole. The size factor had the greatest effect on buckling risk, followed by the form factor and the modulus of elasticity of the wood. Therefore, estimates of buckling risk must consider not only the wood properties but especially the form factor. Finally, we proposed a simple but accurate method of assessing tree buckling risk that is applicable to a wide range of samples and that requires mostly nondestructive measurements.

title: Influence of Tissue Density-specific Mechanical Properties on the Scaling of Plant Height
abstract: Tissue density, ρ, Young's modulus, E, breaking stress, σ, density-specific stiffness (E/ρ), and density-specific strength (σ/ρ) were determined for specimens of parenchyma, collenchyma, primary tracheids, sclerenchyma, and wood. E and σ were positively correlated with ρ for parenchyma and wood. Although no correlation between E or σ and ρ was seen for the other tissue-types, E and σ were correlated for each tissue-type (an inverse proportionality was observed for parenchyma in contrast to the other four tissue-types). Comparisons among the five tissue-types showed that E and σ are inversely proportional to ρ. Parenchyma tissue samples had the lowest E and σ and the highest ρ; wood sample had the highest E and σ and the lowest ρ. Comparisons among tissue-types indicated that σ scales roughly to the square root of E (i.e., σ = 0·69 1·51, r2 = 0·98; units in MN m-2). Also, σ/ρ = 0·03 (E/ρ)0·52 (r2 = 0·99). The interspecific scalling of plant height h with respect to stem diameter d (data taken from Niklas, 1993) was evaluated in terms of E /ρ and σ/ρ by assuming that certain tissue-types characterized the anatomy of the vertical stems of different plant groups (e.g., parenchyma for moss setae, primary tracheids for herbaceous dicotyledon stems, and wood for gymnosperm and dicotyledon tree trunks). The mean E /ρ or σ/ρ for each tissue-type was used to estimate h based mean d for each plant group. Regression of predicted h vs. d gave h ∝ d1·01. Regression of observed average h vs. observed average d showed that h ∝ d1·00. Based on the similarity of the scaling exponents, it is argued that the interspecific scaling of plant height reflects interspecific differences in the anatomy and density-specific mechanical properties of the principle tissue used to provide mechanical support to vertical stems.

title: Associations Between Stem Solidity, Soluble Carbohydrate Accumulation and Other Characters in Wheat
abstract: Studies on the stem characteristics and yields of pith-filled (‘solid’) and hollow-stemmed selections from ten crosses between winter wheat genotypes were carried out in experiments in the field in 1976 and 1977. Samples of stems were taken 10–14 days after anthesis when stem weights and the concentration of ethanol-soluble carbohydrates (sugars) they contained were maximum. Although the d. wt per unit length of stem was greater in the solid than in the hollow selections there was no difference between them in maximum stem weight or sugar concentration. Thus there was no difference between them in the maximum amount of sugar they contained. In a separate study, it was found that the pith in the solid-stemmed selections, which consisted of undifferentiated parenchymatous cells, comprised 11 per cent of the total stem d. wt and contained 13 per cent of the sugar in the entire stem. Solid-stemmed selections were shorter at maturity and had narrower stems than their hollow counterparts. Grain yields from the two types were similar in 1976 and 1977. The genetic and environmental determination of stem solidity and the reasons why the character had no effect on yield are discussed. It is suggested that the greater apparent stiffness of solid stems may confer increased resistance to lodging.

title: Mechanical analysis of the bending behaviour of plant stems.
abstract: In order to optimise the processing of stem crops, insight into the deformation behaviour of the crop and the interaction between crop and machine is essential. Most research in the area of mechanical and physical properties of crop stems is focused on characterising the agricultural products to the point of failure using mechanical parameters and empirical relations. No studies have been conducted on the processes which lead to failure of stems and on the processes that take place after failure. In this paper it is shown that the bending behaviour of wheat and barley stalks is very similar to that of steel tubes. Two consecutive phases can be distinguished: ovalisation and buckling. During ovalisation the forces on the wall tend to flatten the cross-section. When this process continues the flexural stiffness is reduced until the structure becomes unstable and buckles. The cross-section locally completely flattens. This deformed cross-section offers virtually no resistance to bending. Mechanical models described in literature have successfully been adapted to describe the bending behaviour of crop stalks during both phases ( R 2 > 0.98 for ovalisation and R 2 > 0.97 for buckling). The crop species, growing conditions, stem diameter and wall thickness were found to influence the bending process significantly. The presence of a core-rind structure increases the bending resistance of the stems.

title: Review: Wind impacts on plant growth, mechanics and damage.
abstract: Land plants have adapted to survive under a range of wind climates and this involve changes in chemical composition, physical structure and morphology at all scales from the cell to the whole plant. Under strong winds plants can re-orientate themselves, reconfigure their canopies, or shed needles, leaves and branches in order to reduce the drag. If the wind is too strong the plants oscillate until the roots or stem fail. The mechanisms of root and stem failure are very similar in different plants although the exact details of the failure may be different. Cereals and other herbaceous crops can often recover after wind damage and even woody plants can partially recovery if there is sufficient access to water and nutrients. Wind damage can have major economic impacts on crops, forests and urban trees. This can be reduced by management that is sensitive to the local site and climatic conditions and accounts for the ability of plants to acclimate to their local wind climate. Wind is also a major disturbance in many plant ecosystems and can play a crucial role in plant regeneration and the change of successional stage.

title: Agronomic evaluation and performance of flax varieties for industrial fibre production
abstract: Flax fibre for industrial purposes differs from that for linen production, although the agronomic factors that influence fibre development and which factors are most important for industrial fibre production have still to be defined. A description of variations in the performance of fibre flax varieties is also necessary as current guidance relates to the European market rather than the UK. Field trials were sown in 2002 and 2003 at the Henfaes Research Centre in north Wales, investigating 29 and 26 varieties, respectively, of European fibre flax and dual-purpose flax varieties. In 2002 a nitrogen treatment was included in the trial with two treatments, 40 kg/ha and 80 kg/ha. Varieties were evaluated for 20 agronomic and fibre production variables, and the differences between the varieties were analysed using analysis of variance (ANOVA) and principal components analysis (PCA). The higher nitrogen rate was found to increase crop lodging, although some varieties were found to be more susceptible than others. Environment had a strong influence on crop success, with some varieties showing more year to year stability than others. PCA allowed those varieties that were the highest yielding, highest fibre producers and showed the best stability across the 2 years to be identified. Understanding the agronomic results presented and discussed here is important if fibre flax production is to become economically viable in the UK.

title: Does the present trend to select for resistance to lodging in flax involve dangers of a loss in quality?
abstract: With increasing fertility, heavy manuring and mechanical harvesting, flax growers are attaching more value than before to the choosing of varieties which are resistant to lodging. A similar trend can be observed in cereals . Under these circumstances it is likely that flax breeders, like their colleagues the cereal breeders, will pay increasing attention to the ability of their selections to resist lodging . However, the problem in flax is different from that in cereals. In the latter the straw is, so to speak, the support for the ear and the contained grain is of primary importance to the farmer who sets a much lower value on the quantity and quality of the straw . In consequence, most of the new varieties are of the short-strawed type and many breeders are of the opinion that it is easier to breed for resistance to lodging with short rather than long-strawed material. In direct contrast, the stem is the main centre of interest to the flax breeder for the quantity and quality of the straw are the criteria by which the farmer judges success . For a heavy yield straw length is of major significance but as the stem length increases there is also a need for the stiffness to increase if lodging is to be avoided . A different line of reasoning can also be advanced, namely, that a short, stiff strawed variety can withstand heavier manuring or, conversely, that a long, weak-strawed variety can be prevented from lodging by a judicious choice of the field and the appropriate light manuring. It is, however, common knowledge that with a variable crop like flax it is not easy to match the agronomic conditions to the requirements of the plant . With a stiff variety there is undoubtedly less danger than with a weak-stemmed variety . However, in breeding for resistance to lodging the following important question arises . Is it possible to increase the stiffness of the straw without diminishing either the percentage of fibre or its quality, and, if so, to what extent? The answer is of especial importance to the processors who aim at obtaining from a given amount of straw the highest possible yield of fibre of the best quality. On the other hand, the farmer is inclined to concentrate on a heavy yield of straw of good appearance . With such a crop there is, however, no guarantee that either the yield of fibre will be high or the quality good . For all crops where the growing and the processing are in different hands the danger exists that farmer's and manufacturer's interests diverge . When sugar beet was only paid on a weight basis the grower aimed at harvesting a maximum tonnage. On the other hand, the manufacturer was interested in the first place in a high percentage of sugar . However, by means of a payment based in part on sugar content a satisfactory solution has now been found . For flax a comparable system does not exist . In the first place it is no easy matter to determine the percentage of fibre . Moreover,

title: Influence of the morphology characters of the stem on the lodging resistance of Marylin flax
abstract: a b s t r a c t Flax fibres are widely used for composites reinforcement. Within the plant, these fibres have a mechanical support role for the stem, participating especially in the resistance against lodging. Flax stems (Linum usitatissimum) of the Marylin variety were cultivated in the same geographical zone over 4 successive years. Various parameters influencing the stem stiffness were analysed: the height and the diameter of the stems, their internal organization including the proportion of fibre bundles, the diameter and mechanical properties of elementary fibres. It was shown that the fibre yield and number of fibres increased with the height of the plants, the number of fibres being maximal at medium height. In addition, the fibres' diameter decreases with the height of the stem because of the growth mechanisms. No correlation was found between the fibres' mechanical properties and the height of the plants. Lastly, flexural tests on stems made it possible to correlate their stiffness with the Young modulus of the elementary fibres as well as their internal organization. This result confirmed the crucial role of fibres in the support of the plant and in particular in the lodging behaviour.

title: Thigmomorphogenesis: The response of plant growth and development to mechanical stimulation
abstract: SummaryWhen young plants of Hordeum vulgare. Bryonia dioica. Cucumis sativus. Phaseolus vulgaris. Mimosa pudica. and Ricinus communis. were given a gentle mechanical stimulus by rubbing the internodes for about 10 s once or twice daily, elongation was significantly retarded. Plants of Cucurbita pepo Pisum sativum and Triticum aestivum did not exhibit any such response. The initial response to rubbing was very rapid, elongation stopping less than 3 min after application of the stimulus. When the stimulus was discontinued after 7 days, elongation accelerated, reaching a normal or supernormal rate within 3 or 4 days. Mechanical stimulation also affected aspects of growth and development other than stem elongation. In Mimosa pudica, flower bud production was retarded, as was the growth of the tendrils, leaves, and petioles in Bryonia dioica. It is suggested that this response be called thigmomorphogenesis, and that it represents an adaptation designed to protect plants from the stresses produced by high winds and moving animals. Some evidence indicates that thigmomorphogenesis may be mediated by ethylene.

title: The effects of mechanically-induced stress in plants — a review
abstract: Mechanically-induced stress (MIS) occurs naturally in plants as the aerial parts are moved, usually by wind, but also by such agents as rain and animals. It can be induced indoors by various actions such as rubbing or bending the stem or shaking or brushing the entire shoot. The most noticeable effect of MIS is a reduction in stem, leaf or petiole length invariably resulting in plants which are smaller and more compact than unstressed controls. However, the response of other variables can often differ between species and there may be either increases or decreases in stem or petiole diameter, root: shoot weight ratio, chlorophyll content or drought resistance. Why species should differ in this way, and what is the endogenous control mechanism for MIS responses, are inanswered questions. Ethylene, which increases as a result of MIS in several species may cause some MIS responses such as increased stem diameter, epinasty or a change in sex expression. However, evidence suggests that MIS retardation of extension growth may equally be due to lower or supraoptimal auxin levels or lower gibberellin levels.The uses in the field of the growth promoter gibberellin or the growth retardant chlormequat chloride (CCC) appear to be examples of respectively reversing or stimulating MIS growth response. MIS may be applied indoors if short compact plants are needed, either for aesthetic purposes as with floral crops, or if hardier and more manageable plants are needed, such as seedlings for transplanting in the field. Much more research is needed to estimate the importance of MIS in the field and to assess how such knowledge may be used to improve crop yield.

title: Individual-tree radial growth in a subtropical broad-leaved forest: The role of local neighbourhood competition
abstract: Establishing the competitive relationships at the local neighbourhood level is essential for improving our understanding of tree growth dynamics in structurally heterogeneous and species-rich forests. We studied the competitive interactions influencing individual-tree five-year radial growth of the two species Castanopsis fargesii (Franch.) and Quercus fabri (Hance) in a diverse young secondary evergreen broad-leaved forest (EBLF) in eastern China. Different spatially explicit individual-based competition indices were examined for their effectiveness at predicting radial growth. These indices were based on one of the three tree size variables – diameter at breast height (dbh), total height, and crown projection area – and were combined with different approaches to identify potential competitors. Furthermore, we tested for competitive equivalence of conspecific and heterospecific neighbours and analysed the effects of local diversity, initial dbh (measured at the beginning of the five-year growth period) and abiotic environmental variables on individual-tree radial growth. Competition accounted for up to 78% and 75% of radial growth variation in C. fargesii and Q. fabri, respectively. The best results were provided by competition indices using crown projection area as the variable describing tree size and the angular height method as the approach to identify potential competitors (i.e. neighbours greater than the minimum angular height, measured from the base of the target trees, are selected as competitors). Competitive equivalence of conspecific and heterospecific neighbours was found in C. fargesii, whereas heterospecifics were stronger competitors than conspecifics in Q. fabri. We could not detect diversity effects on radial growth. The addition of initial dbh or abiotic environmental variables as further explanatory variables failed to improve the predictive ability of growth models. Our results indicate that diameter growth in this EBLF is largely a function of local neighbourhood competition and suggest that the mode of competition is primarily size-asymmetric. It appears that there may be high competitive equivalence among different species, but this remains to be experimentally tested.

title: Integrative Mechanobiology of Growth and Architectural Development in Changing Mechanical Environments
abstract: Mechanosensitive control of plant growth is a major process shaping how terrestrial plants acclimate to the mechanical challenges set by wind, self-weight, and autostresses. Loads acting on the plant are distributed down to the tissues, following continuum mechanics. Mechanosensing, though, occurs within the cell, building up into integrated signals; yet the reviews on mechanosensing tend to address macroscopic and molecular responses, ignoring the biomechanical aspects of load distribution to tissues and reducing biological signal integration to a “mean plant cell.” In this chapter, load distribution and biological signal integration are analyzed directly. The Sum of Strain Sensing model S 3 m is then discussed as a synthesis of the state of the art in quantitative deterministic knowledge and as a template for the development of an integrative and system mechanobiology.

title: Seeding rate and row spacing affect flax yields and weed interference
abstract: Seeding rate and row spacing are management practices that affect flax seed yield. Two experiments were conducted from 1988 to 1990 to determine the influence of flax seeding rates (300, 600, and 900 seeds m−2) and row spacings (9, 18, and 27 cm). One was a flax-weed interference study (three sites) and the other was a weed-free study (13 sites). In the presence of weeds, increasing seeding rate from 300 to 900 seeds m−2 improved flax seed yield by 180 kg ha−1, and reduced broadleaf weed yields by 300 kg ha−1 and grassy weed yields by 180 kg ha−1. In weed-free conditions, seed yield was not affected by seeding rate. Row spacing did not affect flax yield and had minor effects on weed yields when weeds were not controlled. When weeds were controlled, seed yield in the 9-cm row spacing was 9% (15% in the flax-weed interference study) greater than in the two wider row spacings. Seeding rate and row spacing independently influenced flax yield, and their effect was consistent among sites with weeds present, but...

title: EFFECT OF SEEDING RATE ON PLANT AND SEED CHARACTERISTICS OF NEW FLAX CULTIVARS
abstract: Five flax (Linum usitatissimum L.) cultivars, Dufferin, McGregor, Linott, NorLin and NorMan were grown in the field in 1985, 1986 and 1987 at seeding rates of 200, 400, 600 and 800 seeds m−2. Averaged over all cultivars and years, as seeding rate increased from 200 to 800 seeds m−2, maturity was hastened 2.1 d, seed weight decreased 0.16 g 1000−1 seeds, oil content decreased 0.6%, iodine number decreased 1.3 units and volume weight was not markedly changed. Lodging increased and basal branching decreased from 1.68 to 0.18 branches per plant as seeding rate increased. Plant height increased 0.6 cm from the 200 to the 400 seeds m−2 rate then decreased 1.8 cm from the 400 to the 800 seeds m−2 rate. Seed yield increased from 110 to 124 g m−2 as seeding rate increased from 200 to 600 seeds m−2, then decreased to 121 g m−2 at 800 seeds m−2. Although yields of the five cultivars varied somewhat in their response to seeding rate and year, most yielded near optimum at the 600 seeds m−2 seeding rate. Flax...

title: Influence of seeding depth and seedbed preparation on establishment, growth and yield of fibre flax (Linum usitatissimum L.) in Eastern Canada
abstract: Research was conducted at the Macdonald Campus of McGill University (Quebec, Canada) at three sites in 1997 and one site in 1998 to determine the effects and interac- tions of seeding depth (0, 1, 2, 4 or 6 cm) and seedbed preparation (i.e. soil rolling): none, rolling before or rolling after seeding on fibre flax (cv. Ariane) establishment, growth and yield. Seedbed preparation had little impact on the parameters measured while seeding depth had a variable effect on plant density, plant height, stem diameter and retted straw yield. Seeding depths of 1-4 cm provided consistently good establishment, growth and yield results. In 1997, there was an interaction between seeding depth and seedbed preparation on plant height, branching ratio and retted straw yield, although results were generally variable and tended to be site-specific. In 1998, there was an interaction between seeding depth and seedbed preparation on plant height and stem diameter prior to harvest, with the results varying for all seeding depth-seedbed preparation treatment combinations except for the 2-cm depth treat- ment. Rolling of the seedbed before seeding on lighter soils and at a depth of 2 cm on most soils can improve establishment, growth and yields of fibre flax under eastern Canadian growing conditions.

title: Influence of changing tillage practices on crop production
abstract: The most efficient and practical way of protecting the soil against wind and water erosion is with surface and anchored crop residues. The rate and extent of crop establishment is not adversely affected by conservation tillage provided shallow seeding is used and adequate seed-to-soil contact is achieved. Soil water conservation can be enhanced with conservation tillage systems and the amount conserved is directly influenced by the type and amount of crop residues present and the agro-ecological zone. Crop residue decomposition is 1.5× slower on the surface than when buried and the rate of decomposition can be explained almost entirely by the location and nitrogen content of the residues and growing degree days. Grain yield can be improved with conservation tillage and is directly related to the amount of extra water conserved, regardless of the crop. Crop establishment, which is critical in forage production, can be improved with conservation tillage. Removing forage stands with herbicides as opposed to ...

title: Evaluation of Fibre Flax (Linum usitatissimum L.) Performance under Minimal and Zero Tillage in Eastern Canada
abstract: The feasibility of producing fibre flax in minimum tillage or zero tillage (ZT) systems was investigated. The results were variable between the sites, which differed in soil type and previous cropping history. Tillage regime had no impact on fibre flax phenological development including number of days to emergence, days to flowering and days to harvest at either site. However, tillage regime had a significant effect on mean stem diameter, dry matter content and plant height at all three sampling dates at the sandy loam site, and a significant effect on mid-season plant height at the clay site. At the sandy loam site, ZT plots had the highest populations of plants with the finest stem diameters, the lowest branching ratios, but the shortest plants by the end of the season. Overall, plant densities were greater, stem diameters thinner, and biomass production higher in the heavier soil of the clay site. These results indicate that under the growing conditions present in 1998, fibre flax can successfully be grown in minimum or ZT systems on different soil types in Eastern Canada. Moreover, the growth of fibre flax in these systems does not compromise the proportion of tall plants having thin stems and minimal branching, a critical quality parameter for fibre flax production.

title: A calibrated model of wheat lodging compared with field measurements
abstract: This paper describes how an existing model of lodging in winter wheat (Triticum aestivum L.) has been further developed to enable it to predict the timing and amount of lodging from inputs about the crop, soil and weather. Improvements include the use of recently specified values for the drag coefficient and damping ratio of wheat shoots, accounting for temporal and spatial non-uniformity of plant characteristics, and using daily rainfall and wind run data. Stem and root lodging are predicted when the base bending moment of the shoot(s) exceed the failure moments of the stem base and anchorage system, respectively. Tests show that the model can predict the timing and quantity of lodging in crops with a wide range of lodging risks. Each area of further development contributed to the improvement of the model. Using accurate values of drag coefficient and damping ratio reduced failure wind speeds by 44% to more realistic values. Accounting for temporal non-uniformity of plants meant that the increase in lodging risk towards harvest was correctly predicted. Accounting for spatial non-uniformity enabled different sized areas of lodging to be predicted.

title: Turbulence in plant canopies
abstract: ▪ Abstract The single-point statistics of turbulence in the ‘roughness sub-layer’ occupied by the plant canopy and the air layer just above it differ significantly from those in the surface layer. The mean velocity profile is inflected, second moments are strongly inhomogeneous with height, skewnesses are large, and second-moment budgets are far from local equilibrium. Velocity moments scale with single length and time scales throughout the layer rather than depending on height. Large coherent structures control turbulence dynamics. Sweeps rather than ejections dominate eddy fluxes and a typical large eddy consists of a pair of counter-rotating streamwise vortices, the downdraft between the vortex pair generating the sweep. Comparison with the statistics and instability modes of the plane mixing layer shows that the latter rather than the boundary layer is the appropriate model for canopy flow and that the dominant large eddies are the result of an inviscid instability of the inflected mean velocity profi...

title: A Possible Mechanism for Sensing Crop Canopy Ventilation
abstract: One approach that may help elucidate certain mechanisms of biological sensing is based on a concept developed by engineers in the 1940’s. Operations research seeks to describe the black box or functional behavior of a complex system without determining its exact relationship to the myriad behaviors and interactions of its many components. For example, using this perspective, it may be possible to identify the physical basis underlying sensory capability before identifying the biological pathway by which the sensing occurs at the cellular level. To illustrate this idea, the present Chapter describes a physical process, which provides filtered information that might allow the members of a plant community to monitor the effects of their collective wind-induced motion. Specifically, the energetics of crop canopy ventilation are studied for a wheat crop excited by a non-steady flow. In the model, the wind gust elicits large scale motions facilitating waste gas clearance out of the canopy and into the overlying airspace. As described below, the volumetric flow per unit time is found to be independent of gust velocity but varies in inverse proportion to stalk flexural stiffness. If waste gas clearance represents an important evolutionary constraint, healthy canopy plants may indeed sense intracanopy gas concentration and modulate their biomechanical properties accordingly.

title: Effects of Wind on Plants
abstract: This review surveys the large variety of mechanical interactions between wind and plants, from plant organs to plant systems. These interactions range from leaf flutter to uprooting and seed dispersal, as well as indirect effects on photosynthesis or insect communication. I first estimate the relevant nondimensional parameters and then discuss turbulence, plant dynamics, and the mechanisms of interaction in this context. Some common features are identified and analyzed in relation to the wind engineering of manmade structures. Strong coupling between plants and wind exists, in which the plant motion modifies the wind dynamics. I also present some related biological issues in which the relation between plant life and wind environment is emphasized.

title: Effect of plant interaction on wind-induced crop motion.
abstract: Plant motion due to wind affects plant growth, a phenomenon called thigmomorphogenesis. Despite intensive studies of the turbulence over plant canopies, the study of plant motion induced by wind has often been limited to individual trees or cereal plants. Few models of global canopy motions are available. Moreover the numerical analysis of models that are based on individual stems becomes time consuming when dealing with crops. A model of motion within the canopies is proposed here using a wave propagation equation within a homogenized continuous medium, and a forcing function representing turbulent gusts advected over the canopy. This model is derived from a discrete model of a set of plant shoots represented as individual oscillators, including elastic contacts between shoots. Such contacts induce nonlinearities into the wave equation. A new experimental method to measure stem dynamical properties and elastic collision properties is presented with an illustration on alfalfa stems. Results obtained modeling plant motions in an alfalfa crop are presented.

title: A frequency lock-in mechanism in the interaction between wind and crop canopies
abstract: The interaction between wind dynamics and the waving of crop canopies is explored. On-site experiments with wheat and alfalfa fields have allowed us to quantify the motion of a large set of plants subject to wind, using an image-correlation technique. The coherent part of the waving motion is extracted by a bi-orthogonal decomposition of the spatio-temporal velocity field of the crop surface. It is shown that the corresponding space and time features cannot be explained using predictions from the mixing-layer analogy of wind above canopies, which is the most common model for perturbations in this environment. We show that the plant bending stiffness plays an important role in the frequency and wavelength selection for the coherent motion of the canopy. A fully coupled model, where the wind fluctuations and the plant dynamics interact through a drag term, is then proposed. This model allows us to demonstrate a lock-in mechanism, similar in principle to what is found in vortex-induced vibration, whereby the frequency of the instability deviates from its expected value when approaching the natural frequency of the oscillating medium. This finding is then compared with data from on-site experiments, and good agreement, in both the frequency and wavelength of the propagating patterns observed on the canopy surface, is found.

title: Plant biomechanics and mechanobiology are convergent paths to flourishing interdisciplinary research.
abstract: Over recent decades, there has been a real renaissance of interest in how inner and outer mechanical forces influence biological systems at all scales from macromolecules up to functional ecology. Many areas of animal and medical science are being reshaped by considering biomechanical and mechanobiological aspects, like stiffness-driven differentiation of stem cells, embryo development, tumour invasion, bone and cartilage adaptation, cardiac and arterial remodelling, brain neurobiology, touch and haptics, motion control, and proprioception (e.g. Discher et al., 2005; Stoltz et al., 2005, Boccafoschi et al., 2013; Bukoreshtliev et al., 2013). The same is true and no less impressive in plant sciences where researchers continue to be fascinated by the features that plants have evolved in order to grow and sense, withstand, acclimate, and adapt to the mechanical challenges they face. But what are the major frontiers in plant biomechanics and mechanobiology, the hotspots where physical and biological disciplines cross over? Is this really a new field or can we trace it back in time, and if so, how far? And what exactly do the seemingly mirror-image names biomechanics and mechanobiology mean?

title: Mechanosensing and thigmomorphogenesis, a physiological and biomechanical point of view.
abstract: Plant sensitivity to mechanical stimuli is obvious when observing the movements of Mimosa pudica leaflets when they are touched [1] or those of the Venus fly trap . It is now well established that other plants are also sensitive to mechanical stimuli even if they do not exhibit such rapid movements . There is a renewal of interest in mechanical stimuli as very important cues for the control of plant growth [3] and morphogenesis . This review focuses on mechanosensing in the case of external mechanical loading and its effect on the growth patterns of plant organs (thigmomorphogenesis). The first part of this paper deals with the responses at the whole plant level and their ecological significance. The second part deals with the perception process, with emphasis on the variable that is perceived by the plant. Knowledge about mechanosensors is not presented in great detail because this area of intensive research has been recently reviewed [6,7]. The third part focuses on transduction, i.e., early responses at the cellular level, and particularly focuses on the importance of the kinetics of loading and the kinetics of cellular responses for the interpretation of experimental results. The fourth part focuses on parameters that regulate the mechanosensing process and points out the importance of quantitative studies. Because thigmomorphogenesis and gravitropism are difficult to disentangle, the review ends with data on gravitropism where mechanosensing is involved.

title: Widespread mechanosensing controls the structure behind the architecture in plants.
abstract: Mechanical forces play an instructing role for many aspects of animal cell biology, such as division, polarity and fate. Although the associated mechanoperception pathways still remain largely elusive in plants, physical cues have long been thought to guide development in parallel to biochemical factors. With the development of new imaging techniques, micromechanics tools and modeling approaches, the role of mechanical signals in plant development is now re-examined and fully integrated with modern cell biology. Using recent examples from the literature, I propose to use a multiscale perspective, from the whole plant down to the cell wall, to fully appreciate the diversity of developmental processes that depend on mechanical signals. Incidentally, this also illustrates how conceptually rich this field is.

title: Acclimation of mechanical and hydraulic functions in trees: impact of the thigmomorphogenetic process
abstract: The secondary xylem (wood) of trees mediates several functions including water transport and storage, mechanical support and storage of photosynthates. The optimal structures for each of these functions will most likely differ. The complex structure and function of xylem could lead to trade-offs between conductive efficiency, resistance to embolism, and mechanical strength needed to count for mechanical loading due to gravity and wind. This has been referred to as the trade-off triangle, with the different optimal solutions to the structure/function problems depending on the environmental constraints as well as taxonomic histories. Thus, the optimisation of each function will lead to drastically different anatomical structures. Trees are able to acclimate the internal structure of their trunk and branches according to the stress they experience. These acclimations lead to specific structures that favor the efficiency or the safety of one function but can be antagonistic with other functions. Currently, there are no means to predict the way a tree will acclimate or optimize its internal structure in support of its various functions under differing environmental conditions. In this review, we will focus on the acclimation of xylem anatomy and its resulting mechanical and hydraulic functions to recurrent mechanical strain that usually result from wind-induced thigmomorphogenesis with a special focus on the construction cost and the possible trade-off between wood functions.

title: Mechanical differences between free-standing and supported wheat plants, Triticum aestivum L
abstract: The effect of wind sway on the mechanical characteristics of the anchorage roots and the stem was investigated in mature winter wheat (Triticum aestivumL., cv. Hereward). Wheat plants were field-grown, either supported by a frame, which prevented wind sway, or unsupported (free-standing) and the morphology and mechanical properties of the stems and the anchorage, ‘coronal ’, roots were measured. 
 
Wind sway had little influence on either the stem height or ear weight of the plants but did affect the mechanical properties of the stem. Stems of supported plants were weaker and more flexible than the stems of free-standing plants. There were also differences in the anchorage systems between the treatments: supported plants had just under half as many ‘coronal ’ anchorage roots as the free-standing plants. This reduced the anchorage strength of supported plants by a third. 
 
These differences in mechanical structure meant that the free-standing plants were more resistant to stem buckling and more resistant to anchorage failure. However, considering the difference in the need for mechanical strength in plants from the two regimes, these differences were small. This suggests that wheat has inherent mechanical integrity and, as a monocotyledon with no secondary thickening, it differs little structurally between environments.

title: A comparative study of the response of the roots and shoots of sunflower and maize to mechanical stimulation
abstract: Despite numerous studies of the effects of mechanical stimulation on plant shoots, the response of roots to mechanical stimulation has largely been neglected. In this study the effects of shoot flexure on the morphology and mechanics of two contrasting species of herbaceous angiosperm, growing in a glasshouse were compared : maize (Zea mays), a monocot ; and sunflower (Helianthus annuus L.) a dicot. Mechanical stimulation affected the root more than the shoot components. Root systems of mechanically-stressed sunflowers had a greater angle of spread and increased root number. As well as large morphological and weight effects, with increases over the control of 33% in the length of rigid root and 38% in the dry weight of lateral roots, in sunflowers, there were also mechanical effects. In both species roots of flexed plants were more rigid, stronger and composed of stiffer material and their root systems also provided greater anchorage strength. In contrast, there was only a small reduction in shoot weight and shoot height in flexed plants and no effects on mechanical properties. There were differences in behaviour between species ; maize root morphology responded less than that of sunflowers to mechanical stimulation. The basal diameter of roots increased by only 8% compared with 16% in sunflowers, though the roots of both species showed similar increases in material stiffness. This difference is related to the lack of secondary thickening in the monocots compared with the dicot sunflowers.

title: The effects of air flow and stem flexure on the mechanical and hydraulic properties of the stems of sunflowers Helianthus annuus L.
abstract: Many studies have shown that wind affects plant development, causing them to develop shorter and usually stronger stems. Many of these effects have been shown to be due to a response to mechanical flexing of the stem which is known as thigmomorphogenesis. However, it is not known how wind affects the hydraulic properties of stems, nor have the effects of air flow past leaves been examined in isolation from mechanical flexing. This study, therefore, used a factorial experiment to distinguish between the effects of stem flexing and air flow, and examined the morphology, hydraulics and mechanics of developing sunflowers Helianthus annuus. It was found that flexure and air flow had opposite effects on several aspects of development; air flow increased plant height and length-specific stem hydraulic conductivity, k(h), and reduced stem rigidity and strength, while flexing did the reverse. There was also a clear trade-off between hydraulic and mechanical capability: as one increased the other decreased. A plant's response to wind must, therefore, be a complex response to at least two different stimuli and this might help explain why it varies with species and environment.

title: Ecophysiology of Cecropia schreberiana saplings in two wind regimes in an elfin cloud forest: growth, gas exchange, architecture and stem biomechanics.
abstract: The hypothesis that the short, stunted development of elfin cloud forest trees is influenced by strong winds was tested by studying growth, gas exchange and biomechanics of potted saplings of Cecropia schreberiana Miq. ex. C. peltata L. (Cecropiaceae) exposed to two natural wind regimes (exposed and protected) at high elevation sites in the Luquillo Experimental Forest, Puerto Rico. The wind-exposure treatment produced several thigmomorphogenetic responses, including reductions in plant stature and crown area, changes in allocation patterns, and increased root to shoot ratio, leaf abrasion and leaf epinasty. Wind-exposure decreased maximum photosynthetic rate and respiration on an area basis, but not on a leaf-mass basis. Wind-exposed plants had lower apparent quantum yields, and higher light compensation points than wind-protected plants. Photosynthetic nitrogen-use efficiency was lower in wind-exposed plants, but such plants had higher leaf nitrogen concentration than wind-protected plants. There were no effects of treatments on stomatal conductance, transpiration rate and water-use efficiency. Stems of wind-exposed plants had lower second moment of area, apparent modulus of elasticity, flexural stiffness and stem density, but higher water content than wind-protected plants. Tissue-density-specific stiffness and the calculated critical height were not affected by the treatments. Wind-exposed plants were biomechanically less predisposed to bending and failing under their own weight than wind-protected plants because their safety factors were smaller, indicating that maintenance of an ontogenetically less developed structure enables plants to cope with wind loading. Windward trees showed a lower scaling component of the allometric relationship between diameter and height than leeward trees.

title: Thigmomorphogenesis: the effect of mechanical perturbation on plants
abstract: Thigmomorphogenetic responses occur in many environmental settings. The most pronounced effects are found under conditions of extremely high rates of turbulent wind or water flow. However, it is an ubiquitous phenomenon, since mechanical perturbations are to be encountered under all but the most stringent laboratory conditions. Our present understanding of these phenomena is the result of studies at the ecological, anatomical, physiological, biochemical, biophysical and molecular biological levels.

title: Thigmomorphogenesis: anatomical, morphological and mechanical analysis of genetically different sibs of Pinus taeda in response to mechanical perturbation.
abstract: Twenty-three open pollinated families (half-sibs) and four controlled pollinated families (full-sibs) of Pinus taeda L. (loblolly pine) were grown in a greenhouse and analyzed for changes induced by mechanical perturbation (MP). These changes included inhibition of stem and needle elongation, bracing of branch nodes, and increased radial growth in the direction of the MP. Inhibition of stem elongation was the least variable feature measured. Leaf extension and stem diameter were highly variable between half-sibs. MP induced increased drag in greenhouse grown P. taeda in wind-tunnel tests. In P. taeda, MP induced decreased flexibility and increased elasticity and plasticity of the stem. The increased radial growth of the stems overrode the increase in elasticity, resulting in an overall decrease in flexibility. MP trees had a higher rupture point than non-MP controls. Increased radial growth is a result of more rapid cell divisions of the vascular cambium, resulting in increased numbers of tracheids. The decreased leader growth is partly due to a decreased tracheid length in response to MP.

title: Traits, properties, and performance: how woody plants combine hydraulic and mechanical functions in a cell, tissue, or whole plant.
abstract: This review presents a framework for evaluating how cells, tissues, organs, and whole plants perform both hydraulic and mechanical functions. The morphological alterations that affect dual functionality are varied: individual cells can have altered morphology; tissues can have altered partitioning to functions or altered cell alignment; and organs and whole plants can differ in their allocation to different tissues, or in the geometric distribution of the tissues they have. A hierarchical model emphasizes that morphological traits influence the hydraulic or mechanical properties; the properties, combined with the plant unit's environment, then influence the performance of that plant unit. As a special case, we discuss the mechanisms by which the proxy property wood density has strong correlations to performance but without direct causality. Traits and properties influence multiple aspects of performance, and there can be mutual compensations such that similar performance occurs. This compensation emphasizes that natural selection acts on, and a plant's viability is determined by, its performance, rather than its contributing traits and properties. Continued research on the relationships among traits, and on their effects on multiple aspects of performance, will help us better predict, manage, and select plant material for success under multiple stresses in the future.

title: Gravitropism in higher plants.
abstract: Since 1806, we have known that plant organs use gravity as a guide for growth ([Knight, 1806][1]). The gravity-directed growth process, called gravitropism, dictates upward shoot growth to ensure a proper positioning of the leaves for efficient photosynthesis and gas exchange. It also directs roots

title: Inclination not force is sensed by plants during shoot gravitropism
abstract: Gravity perception plays a key role in how plants develop and adapt to environmental changes. However, more than a century after the pioneering work of Darwin, little is known on the sensing mechanism. Using a centrifugal device combined with growth kinematics imaging, we show that shoot gravitropic responses to steady levels of gravity in four representative angiosperm species is independent of gravity intensity. All gravitropic responses tested are dependent only on the angle of inclination from the direction of gravity. We thus demonstrate that shoot gravitropism is stimulated by sensing inclination not gravitational force or acceleration as previously believed. This contrasts with the otolith system in the internal ear of vertebrates and explains the robustness of the control of growth direction by plants despite perturbations like wind shaking. Our results will help retarget the search for the molecular mechanism linking shifting statoliths to signal transduction.

title: Transcriptional and Hormonal Regulation of Gravitropism of Woody Stems in Populus[OPEN]
abstract: Fundamental mechanisms associated with gravitropism in woody stems of Populus involve relocalization of the PIN3 auxin transporter and interacting roles for auxin, gibberellic acid, and the ARBORKNOX2 transcription factor in regulating fiber development and gravibending. Angiosperm trees reorient their woody stems by asymmetrically producing a specialized xylem tissue, tension wood, which exerts a strong contractile force resulting in negative gravitropism of the stem. Here, we show, in Populus trees, that initial gravity perception and response occurs in specialized cells through sedimentation of starch-filled amyloplasts and relocalization of the auxin transport protein, PIN3. Gibberellic acid treatment stimulates the rate of tension wood formation and gravibending and enhances tissue-specific expression of an auxin-responsive reporter. Gravibending, maturation of contractile fibers, and gibberellic acid (GA) stimulation of tension wood formation are all sensitive to transcript levels of the Class I KNOX homeodomain transcription factor-encoding gene ARBORKNOX2 (ARK2). We generated genome-wide transcriptomes for trees in which gene expression was perturbed by gravistimulation, GA treatment, and modulation of ARK2 expression. These data were employed in computational analyses to model the transcriptional networks underlying wood formation, including identification and dissection of gene coexpression modules associated with wood phenotypes, GA response, and ARK2 binding to genes within modules. We propose a model for gravitropism in the woody stem in which the peripheral location of PIN3-expressing cells relative to the cambium results in auxin transport toward the cambium in the top of the stem, triggering tension wood formation, while transport away from the cambium in the bottom of the stem triggers opposite wood formation.

title: Auxins and Tropisms
abstract: Differential growth of plants in response to the changes in the light and gravity vectors requires a complex signal transduction cascade. Although many of the details of the mechanisms by which these differential growth responses are induced are as yet unknown, auxin has been implicated in both gravitropism and phototropism. Specifically, the redistribution of auxin across gravity or light-stimulated tissues has been detected and shown to be required for this process. The approaches by which auxin has been implicated in tropisms include isolation of mutants altered in auxin transport or response with altered gravitropic or phototropic response, identification of auxin gradients with radiolabeled auxin and auxin-inducible gene reporter systems, and by use of inhibitors of auxin transport that block gravitropism and phototropism. Proteins that transport auxin have been identified and the mechanisms which determine auxin transport polarity have been explored. In addition, recent evidence that reversible protein phosphorylation controls this process is summarized. Finally, the data in support of several hypotheses for mechanisms by which auxin transport could be differentially regulated during gravitropism are examined. Although many details of the mechanisms by which plants respond to gravity and light are not yet clear, numerous recent studies demonstrate the role of auxin in these processes.

title: The Gravitropic Response of Poplar Trunks: Key Roles of Prestressed Wood Regulation and the Relative Kinetics of Cambial Growth versus Wood Maturation[C][OA]
abstract: In tree trunks, the motor of gravitropism involves radial growth and differentiation of reaction wood (Archer, 1986). The first aim of this study was to quantify the kinematics of gravitropic response in young poplar (Populus nigra x Populus deltoides, ‘I4551’) by measuring the kinematics of curvature fields along trunks. Three phases were identified, including latency, upward curving, and an anticipative autotropic decurving, which has been overlooked in research on trees. The biological and mechanical bases of these processes were investigated by assessing the biomechanical model of Fournier et al. (1994). Its application at two different time spans of integration made it possible to test hypotheses on maturation, separating the effects of radial growth and cross section size from those of wood prestressing. A significant correlation between trunk curvature and Fournier's model integrated over the growing season was found, but only explained 32% of the total variance. Moreover, over a week's time period, the model failed due to a clear out phasing of the kinetics of radial growth and curvature that the model does not take into account. This demonstrates a key role of the relative kinetics of radial growth and the maturation process during gravitropism. Moreover, the degree of maturation strains appears to differ in the tension woods produced during the upward curving and decurving phases. Cell wall maturation seems to be regulated to achieve control over the degree of prestressing of tension wood, providing effective control of trunk shape.

title: Unifying model of shoot gravitropism reveals proprioception as a central feature of posture control in plants
abstract: Gravitropism, the slow reorientation of plant growth in response to gravity, is a key determinant of the form and posture of land plants. Shoot gravitropism is triggered when statocysts sense the local angle of the growing organ relative to the gravitational field. Lateral transport of the hormone auxin to the lower side is then enhanced, resulting in differential gene expression and cell elongation causing the organ to bend. However, little is known about the dynamics, regulation, and diversity of the entire bending and straightening process. Here, we modeled the bending and straightening of a rod-like organ and compared it with the gravitropism kinematics of different organs from 11 angiosperms. We show that gravitropic straightening shares common traits across species, organs, and orders of magnitude. The minimal dynamic model accounting for these traits is not the widely cited gravisensing law but one that also takes into account the sensing of local curvature, what we describe here as a graviproprioceptive law. In our model, the entire dynamics of the bending/straightening response is described by a single dimensionless “bending number” B that reflects the ratio between graviceptive and proprioceptive sensitivities. The parameter B defines both the final shape of the organ at equilibrium and the timing of curving and straightening. B can be estimated from simple experiments, and the model can then explain most of the diversity observed in experiments. Proprioceptive sensing is thus as important as gravisensing in gravitropic control, and the B ratio can be measured as phenotype in genetic studies.

title: Plastids and gravitropic sensing
abstract: Data and theories about the identity of the mass that acts in gravitropic sensing are reviewed. Gravity sensing may have evolved several times in plants and algae in processes such as gravitropism of organs and tip-growing cells, gravimorphism, gravitaxis, and the regulation of cytoplasmic streaming in internodal cells of Chara. In the latter and in gravitaxis, the mass of the entire cell may function in sensing. But gravitropic sensing appears to rely upon the mass of amyloplasts that sediment since (i) the location of cells with sedimentation is highly regulated, (ii) such cells contain other morphological specializations favoring sedimentation, (iii) sedimentation always correlates with gravitropic competence in wild-type plants, (iv) magnetophoretic movement of rootcap amyloplasts mimics gravitropism, and (v) starchless and intermediate starch mutants show reduced gravitropic sensitivity. The simplest interpretation of these data is that gravitropic sensing is plastid-based.

title: Genetic evidence that the endodermis is essential for shoot gravitropism in Arabidopsis thaliana.
abstract: Shoots of higher plants exhibit negative gravitropism. However, little is known about the mechanism or site of gravity perception in shoots. We have identified two loci that are essential for normal shoot gravitropism in Arabidopsis thaliana. Genetic analysis demonstrated that the shoot gravitropism mutants sgr1 and sgr7 are allelic to the radial pattern mutants, scr and shr, respectively. Characterization of the aerial phenotype of these mutants revealed that the primary defect is the absence of a normal endodermis in hypocotyls and influorescence stems. This indicates that the endodermis is essential for shoot gravitropism and strongly suggests that this cell layer functions as the gravity-sensing cell layer in dicotyledonous plant shoots. These results also demonstrate that, in addition to their previously characterized role in root radial patterning, SCR and SHR regulate the radial organization of the shoot axial organs in Arabidopsis.

title: Signal perception, transduction, and response in gravity resistance. Another graviresponse in plants
abstract: Resistance to the gravitational force is a serious problem that plants have had to solve to survive on land. Mechanical resistance to the pull of gravity is thus a principal graviresponse in plants, comparable to gravitropism. Nevertheless, only limited information has been obtained for this gravity response. We have examined the mechanism of gravity-induced mechanical resistance using hypergravity conditions produced by centrifugation. As a result, we have clarified the outline of the sequence of events leading to the development of mechanical resistance. The gravity signal may be perceived by mechanoreceptors (mechanosensitive ion channels) on the plasma membrane and it appears that amyloplast sedimentation in statocytes is not involved. Transformation and transduction of the perceived signal may be mediated by the structural or physiological continuum of microtubule–cell membrane–cell wall. As the final step in the development of mechanical resistance, plants construct a tough body by increasing cell wall rigidity. The increase in cell wall rigidity is brought about by modification of the metabolism of certain wall constituents and modification of the cell wall environment, especially pH. We need to clarify the details of each step by future space and ground-based experiments.

title: Directional gravity sensing in gravitropism.
abstract: Plants can reorient their growth direction by sensing organ tilt relative to the direction of gravity. With respect to gravity sensing in gravitropism, the classic starch statolith hypothesis, i.e., that starch-accumulating amyloplast movement along the gravity vector within gravity-sensing cells (statocytes) is the probable trigger of subsequent intracellular signaling, is widely accepted. Several lines of experimental evidence have demonstrated that starch is important but not essential for gravity sensing and have suggested that it is reasonable to regard plastids (containers of starch) as statoliths. Although the word statolith means sedimented stone, actual amyloplasts are not static but instead possess dynamic movement. Recent studies combining genetic and cell biological approaches, using Arabidopsis thaliana, have demonstrated that amyloplast movement is an intricate process involving vacuolar membrane structures and the actin cytoskeleton. This review covers current knowledge regarding gravity sensing, particularly gravity susception, and the factors modulating the function of amyloplasts for sensing the directional change of gravity. Specific emphasis is made on the remarkable differences in the cytological properties, developmental origins, tissue locations, and response of statocytes between root and shoot systems. Such an approach reveals a common theme in directional gravity-sensing mechanisms in these two disparate organs.

title: Asymmetric expression of a poplar ACC oxidase controls ethylene production during gravitational induction of tension wood.
abstract: Ethylene is produced in wood-forming tissues, and when applied exogenously, it has been shown to cause profound effects on the pattern and rate of wood development. However, the molecular regulation of ethylene biosynthesis during wood formation is poorly understood. We have characterised an abundant 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene (PttACO1) in the wood-forming tissues of Populus tremula (L.) x P. tremuloides (Michx). PttACO1 is primarily expressed in developing secondary xylem, and is specifically upregulated during secondary wall formation. Nevertheless, according to GC-MS analysis combined with tangential cryosectioning, the distribution of ACC was found to be fairly uniform across the cambial-region tissues. Gravitational stimulation, which causes tension wood to form on the upper side of the stem, resulted in a strong induction of PttACO1 expression and ACC oxidase activity in the tension wood-forming tissues. The ACC levels increased in parallel to the PttACO1 expression. However, the increase on the upper (tension wood) side was only minor, whereas large amounts of both ACC and its hydrolysable conjugates accumulated on the lower (opposite) side of the stem. This suggests that the relatively low level of ACC on the tension wood side is a result of its conversion to ethylene by the highly upregulated PttACO1, and the concurrent accumulation of ACC on the opposite side of the wood is because of the low PttACO1 levels. We conclude that PttACO1 and ACC oxidase activity, but not ACC availability, are important in the control of the asymmetric ethylene production within the poplar stem when tension wood is induced by gravitational stimulation.

title: Cellular mechanisms underlying growth asymmetry during stem gravitropism
abstract: Plant stems respond to gravitropic stimulation with a rapid, local and reversible change in cell growth rate (elongation), generally on both the upper and lower sides of the stem. The cellular and biochemical mechanisms for this differential growth are reviewed. Considerable evidence implicates an asymmetry in wall pH in the growth response. The strengths and weaknesses of the wall “loosening enzyme” concept are reviewed and the possibility of expansin involvement in the bending response of stems is considered. Also discussed is the possibility that wall stiffening processes, e.g. phenolic coupling driven by oxidative bursts or altered orientation of newly deposited cellulose, might mediate the growth responses during gravitropism.

title: Biomechanical design and long-term stability of trees: morphological and wood traits involved in the balance between weight increase and the gravitropic reaction.
abstract: Studies on tree biomechanical design usually focus on stem stiffness, resistance to breakage or uprooting, and elastic stability. Here we consider another biomechanical constraint related to the interaction between growth and gravity. Because stems are slender structures and are never perfectly symmetric, the increase in tree mass always causes bending movements. Given the current mechanical design of trees, integration of these movements over time would ultimately lead to a weeping habit unless some gravitropic correction occurs. This correction is achieved by asymmetric internal forces induced during the maturation of new wood. The long-term stability of a growing stem therefore depends on how the gravitropic correction that is generated by diameter growth balances the disturbance due to increasing self weight. General mechanical formulations based on beam theory are proposed to model these phenomena. The rates of disturbance and correction associated with a growth increment are deduced and expressed as a function of elementary traits of stem morphology, cross-section anatomy and wood properties. Evaluation of these traits using previously published data shows that the balance between the correction and the disturbance strongly depends on the efficiency of the gravitropic correction, which depends on the asymmetry of wood maturation strain, eccentric growth, and gradients in wood stiffness. By combining disturbance and correction rates, the gravitropic performance indicates the dynamics of stem bending during growth. It depends on stem biomechanical traits and dimensions. By analyzing dimensional effects, we show that the necessity for gravitropic correction might constrain stem allometric growth in the long-term. This constraint is compared to the requirement for elastic stability, showing that gravitropic performance limits the increase in height of tilted stem and branches. The performance of this function may thus limit the slenderness and lean of stems, and therefore the ability of the tree to capture light in a heterogeneous environment.

title: Precautions for the structural analysis of the gelatinous layer in tension wood
abstract: The gelatinous layer (G-layer) of tension wood fibres in hardwood contributes to the mechanical function of the living tree and has significant consequences on properties of solid wood. Its size, shape and structure observed by optical or electron microscopy exhibits characteristic anatomical features. However, we found that sectioning of non-embedded wood samples results in an uncontrolled swelling of the G-layer. In order to assess this artefact, the shape and thickness of the G-layer was monitored by serial sections from an embedded wood sample, from its trimmed transverse face to that located several hundreds of micrometres deep. The results revealed that the initial cutting before embedding produced a border effect responsible for the swollen nature, which is similar to sections from non-embedded material. After a conventional embedding technique was applied, a section of at least 30 micrometres below the trimming surface is required to observe an un-swollen G-layer.

title: Induction of Tension Wood with the Antiauxin 2,3,5-Tri-iodobenzoic acid
abstract: THE xylem formed on the upper side of arborescent angiosperms in reaction to inclination is often of the abnormal tension wood type. A complete discussion of tension wood anatomy is given in a recent review by Wardrop1. In brief, it is characterized by the presence of a large number of thick-walled, ‘gelatinous’ fibres of unusually low lignin content, and a reduction in the size and number of vessels over that of normal wood.

title: Modelling of auxin transport affected by gravity and differential radial growth.
abstract: When a tree stem deviates from verticality, as a result of different environmental factors, patterns of differential radial growth appear. Higher rates of wood production have been observed on the lower side of the tree and lower rates in the opposite side. Biological studies on plant hormones have shown that the concentration of auxin induces radial growth. They also have demonstrated the redistribution of auxin transport in response to gravity. Auxin is then designated as a mediator for differential growth. This paper presents a model for three-dimensional (3-D) auxin transport in conifer trees, which includes gravity dependence. We obtain realistic heterogeneous patterns of auxin distribution over the tree. Then, we propose a law of growth based on auxin concentration to simulate successive differential radial growths. The predicted growths are compared with experimental results of reconstruction of 3-D annual growth of Radiata pine.

title: Occurrence of Reaction Wood in Branches of Dicotyledons and Its Role in Tree Architecture
abstract: Lateral branch and young leader axes of 122 species of dicotyledonous trees in 46 families, displaying a variety of architectural models, were surveyed for presence of reaction wood (RW) as defined by gelatinous wood fibers (G-fibers). Distinct G-fibers occurred in 56 species, mostly in the upper half of the axis. There was a positive correlation between changes in axis orientation and position of the RW in 22, or one-fourth, of the species showing changes in branch orientation. Many species show an increase in branch angle; i.e., branches become more horizontal with age. Among these, Hevea (Rauh's architectural model), Endospermum, and Terminalia (both Aubreville's model) first produce RW on the lower side near the pith and later on the upper side. The erection of a lateral branch, i.e., a decrease in branch angle, to form the new leader in Koriba's model is correlated with RW on the upper side of the branch in Hura, but not in other species with this model. Many species with Troll's model, in which the arched leader becomes vertical, have RW on the upper side of the leader axis, e.g., Hymenaea, Fagus, Banara, Celtis, Ulmus, Piscidia, and Brownea. In some species with Koriba's or Troll's models, the wood on the upper side is thinner walled and less lignified, and the phloem rays are longer radially and more dilated tangentially than on the lower side of the axes. Thus, in some trees the normal reorientation of woody axes is related to the distribution of G-fibers, which cause longitudinal tensile stress, and/or other anatomical differences within those axes. This suggests an active, endogenous role for RW in the establishment of the architecture of these examples, in addition to its previously known supportive role in horizontal and displaced axes.

title: GROWTH STRESSES ARE HIGHLY CONTROLLED BY THE AMOUNT OF G-LAYER IN POPLAR TENSION WOOD.
abstract: To determine how gelatinous fibres and gelatinous layers contribute to the magnitude of longitudinal growth stress in tension wood, anatomical measurements of gelatinous fibres were carried out on poplar tension wood (Populus I4551). It was found that (a) no gelatinous fibres were observed under a growth strain level of 0.06 to 0.08%; (b) almost 100% of the non-conductive tissues contained gelatinous fibres above a growth strain level of 0.15 to 0.19%; and (c) the area of fibres, the area of fibres with gelatinous layers per unit of tissue area, and the thickness of the gelatinous layers predominantly influenced the magnitude of growth stress

title: Poplar genes encoding fasciclin-like arabinogalactan proteins are highly expressed in tension wood.
abstract: Fifteen poplar cDNA encoding fasciclin-like arabinogalactan proteins (PopFLAs) were finely characterized, whereas the presence of arabinogalactan proteins (AGPs) was globally assessed during wood formation. •  PopFLAs transcript accumulation was analysed through EST distribution in cDNA libraries, semi-quantitative RT-PCR, microarray experiment and Northern blot analysis. Similarly, AGPs contents were globally quantified by rocket electrophoresis. AGPs accumulation was further examined by Western blotting and immunocytolocalization. Ten PopFLAs were specifically expressed in tension wood (TW) and not expressed in the cambial zone. Rocket electrophoresis revealed important AGPs accumulation in TW xylem. An anti-AGPs specific antibody recognized two proteins preferentially present in the cell wall-bound fraction from TW. Immunocytochemistry revealed a strong labelling close to the inner part of the G-layer of TW fibres. PopFLAs are expressed in xylem and many are up-regulated in TW. It is suggested that some PopFLAs accumulating at the inner side of the G-layer may have a specific function in the building of this layer. PopFLAs expression may therefore be linked to the specific mechanical properties of TW.

title: Deposition and organisation of cell wall polymers during maturation of poplar tension wood by FTIR microspectroscopy
abstract: To advance our understanding of the formation of tension wood, we investigated the macromolecular arrangement in cell walls by Fourier transform infrared microspectroscopy (FTIR) during maturation of tension wood in poplar (Populus tremula x P. alba, clone INRA 717-1B4). The relation between changes in composition and the deposition of the G-layer in tension wood was analysed. Polarised FTIR measurements indicated that in tension wood, already before G-layer formation, a more ordered structure of carbohydrates at an angle more parallel to the fibre axis exists. This was clearly different from the behaviour of opposite wood. With the formation of the S2 layer in opposite wood and the G-layer in tension wood, the orientation signals from the amorphous carbohydrates like hemicelluloses and pectins were different between opposite wood and tension wood. For tension wood, the orientation for these bands remains the same all along the cell wall maturation process, probably reflecting a continued deposition of xyloglucan or xylan, with an orientation different to that in the S2 wall throughout the whole process. In tension wood, the lignin was more highly oriented in the S2 layer than in opposite wood.

title: Critical review on the mechanisms of maturation stress generation in trees
abstract: Trees control their posture by generating asymmetric mechanical stress around the periphery of the trunk or branches. This stress is produced in wood during the maturation of the cell wall. When the need for reaction is high, it is accompanied by strong changes in cell organization and composition called reaction wood, namely compression wood in gymnosperms and tension wood in angiosperms. The process by which stress is generated in the cell wall during its formation is not yet known, and various hypothetical mechanisms have been proposed in the literature. Here we aim at discriminating between these models. First, we summarize current knowledge about reaction wood structure, state and behaviour relevant to the understanding of maturation stress generation. Then, the mechanisms proposed in the literature are listed and discussed in order to identify which can be rejected based on their inconsistency with current knowledge at the frontier between plant science and mechanical engineering.

title: Arabidopsis thaliana as a model for gelatinous fiber formation
abstract: Trees and herbaceous plants continuously monitor their position to maintain vertical stem growth and regulate branch orientation. When orientation is altered from the vertical, they form a special type of wood called reaction wood that differs chemically and structurally from normal wood and forces reorientation of the organ or whole plant. The reaction wood of dicotyledons is called tension wood and is characterized by nonlignified gelatinous fibers. The altered chemical and mechanical properties of tension wood reduce wood quality and represent a major problem for the timber and pulping industries. Repeated clipping of the emerging inflorescence stems of Arabidopsis thaliana augments wood formation in organs, including those inflorescence stems that are allowed to develop later. Gravistimulation of such inflorescence stems induces tension wood formation, allowing the use of A. thaliana for a molecular and genetic analysis of the mechanisms of tension wood formation.

title: Reaction tissue formation and stem tensile modulus properties in wild-type and p-coumarate-3-hydroxylase downregulated lines of alfalfa, Medicago sativa (Fabaceae).
abstract: To our knowledge, xylary reaction tissue has never been reported in a forage crop species. Here we report the discovery of reaction tissue in a transgenic line of Medicago sativa (pC3H, for the gene for p-coumarate-3-hydroxylase) with reduced lignin content and in the wild-type (WT) line. Based on microscopy and biomechanical testing of internodal alfalfa branch sections, the transgenic (pC3H-I) line, relative to the WT (1) apparently formed more reaction tissue containing gelatinous fibers with adjacent thick-walled fibers (presumed to be "intermediate" tissue) more rapidly, (2) had more xylem tissue, and (3) had comparable tensile dynamic modulus properties. These findings thus establish the (limited) ability of this perennial angiosperm to form (inducible) reaction tissue in a manner somewhat analogous to that of woody arborescent angiosperms. The potential of effectuating reductions in lignin amounts in (woody) angiosperms with increased formation of reaction (tension wood) tissue is discussed because reaction tissues are often viewed as a deleterious trait in processing for many agronomic/industrial applications, especially with the current interest in biofuels.