bluuebunny/crossref_metadata_2025 huggingface dataset:
Appearance of biomarkers of in vitro ageing after successive stimulation of WI‐38 fibroblasts with IL‐1α and TNF‐α: senescence associated β‐galactosidase activity and morphotype transition
Authors: DUMONT PATRICK , BALBEUR LAURA , REMACLE JOSE , TOUSSAINT OLIVIER
Published: March 2003

Sublethal oxidative stresses increase the proportions of human fibroblasts positive for senescence associated β‐galactosidase activity and accelerate the transition in the fibroblast morphotypes characterising fibroblast ageing. Stimulation of fibroblasts with TNF‐α or IL‐1α transiently increases the production of reactive oxygen species (ROS) in human fibroblasts. Here we propose that repeated stimulation of WI‐38 fibroblasts with TNF‐α or IL‐1α can generate enough ROS to accelerate the transition in the fibroblast morphotypes and increase the proportion of cells positive for senescence associated β‐galactosidase activity. The involvement of ROS is suggested by experiments where the stimulation of fibroblasts with TNF‐α or IL‐1α are performed in the presence of N‐acetylcysteine which increases the intracellular antioxidant potential. It is proposed that the decrease in the proportions of morphotypes I and II, and the increase in the proportions of morphotypes III to VI observed after successive stimulation with TNF‐α or IL1‐α is attributed to an increased ROS production occurring during the stimulation.
Distribution of cartilage thickness on the head of the human first metatarsal bone
Authors: MUEHLEMAN CAROL , KUETTNER KLAUS E.
Published: March 2003

Articular hyaline cartilage takes on the contours of the subchondral bone on which it lies, but its thickness varies between joints, within a single joint and within a single articular surface. Previous studies have correlated articular cartilage thickness distribution with the degree of stress and weight bearing on joint surfaces, but few studies have considered the thickness of the calcified cartilage in relation to these parameters. Here we report a correlation between the cartilage thickness distribution and weight bearing distribution on the head of the 1st metatarsal bone, a component of one of the major weight bearing joints in the lower extremity during the gait cycle. The greatest total and uncalcified articular cartilage thickness was found on the central and lateral distal aspects of the metatarsal head, a region that receives maximal ground reactive force during the propulsive phase of the normal gait cycle. Although the thickness of the calcified cartilage was correlated with the thickness of the uncalcified cartilage, it varied to a lesser extent across the articular surface than did that of the uncalcified cartilage.
The role of the notochord in vertebral column formation
Authors: FLEMING ANGELEEN , KEYNES ROGER J. , TANNAHILL DAVID
Published: March 2003

abstract

The backbone or vertebral column is the defining feature of vertebrates and is clearly metameric. Given that vertebrae arise from segmented paraxial mesoderm in the embryo, this metamerism is not surprising. Fate mapping studies in a variety of species have shown that ventromedial sclerotome cells of the differentiated somite contribute to the developing vertebrae and ribs. Nevertheless, extensive studies in amniote embryos have produced conflicting data on exactly how embryonic segments relate to those of the adult. To date, much attention has focused on the derivatives of the somites, while relatively little is known about the contribution of other tissues to the formation of the vertebral column. In particular, while it is clear that signals from the notochord induce and maintain proliferation of the sclerotome, and later promote chondrogenesis, the role of the notochord in vertebral segmentation has been largely overlooked. Here, we review the established role of the notochord in vertebral development, and suggest an additional role for the notochord in the segmental patterning of the vertebral column.
Thoracic origin of a sympathetic supply to the upper limb: the ‘nerve of Kuntz’ revisited
Authors: RAMSAROOP L. , PARTAB P. , SINGH B. , SATYAPAL K. S.
Published: March 2003

An understanding of the origin of the sympathetic innervation of the upper limb is important in surgical sympathectomy procedures. An inconstant intrathoracic ramus which joined the 2nd intercostal nerve to the ventral ramus of the 1st thoracic nerve, proximal to the point where the latter gave a large branch to the brachial plexus, has become known as the ‘nerve of Kuntz’ (Kuntz, 1927). Subsequently a variety of sympathetic interneuronal connections down to the 5th intercostal space were reported and also described as the nerve of Kuntz. The aim of this study was to determine: (1) the incidence, location and course of the nerve of Kuntz; (2) the relationship of the nerve of Kuntz to the 2nd thoracic ganglion; (3) the variations of the nerve of Kuntz in the absence of a stellate ganglion; (4) to compare the original intrathoracic ramus with sympathetic variations at other intercostal levels; and (5) to devise an appropriate anatomical classification of the nerves of Kuntz.

Bilateral microdissection of the sympathetic chain and somatic nerves of the upper 5 intercostal spaces was undertaken in 32 fetuses (gestational age, 18 wk to full term) and 18 adult cadavers. The total sample size comprised 99 sides.

Sympathetic contributions to the first thoracic nerve were found in 60 of 99 sides (left 32, right 28). Of these, 46 were confined to the 1st intercostal space only. The nerve of Kuntz (the original intrathoracic ramus) of the 1st intercostal space had a demonstrable sympathetic connection in 34 cases, and an absence of macroscopic sympathetic connections in 12. In the remaining intercostal spaces, intrathoracic rami uniting intercostal nerves were not observed. Additional sympathetic contributions (exclusive of rami communicantes) were noted between ganglia, interganglionic segments and intercostal nerves as additional rami communicantes. The eponym nerve of Kuntz should be restricted to descriptions of the intrathoracic ramus of the 1st intercostal space. Any of these variant sympathetic pathways may be responsible for the recurrence of symptoms after sympathectomy surgery.
Hypertrophy of mucosa and serosa in the obstructed intestine of rats
Authors: BERTONI SIMONA , GABELLA GIORGIO
Published: March 2003

After a surgically induced partial obstruction of the small intestine (ileum) in adult rats there is an accumulation of ingesta and a progressive enlargement of the lumen accompanied by wall thickening: over a period of 2–3 wk the circumference of the hypertrophic intestine increases by a factor of 2·7 and the thickness of the musculature increases more than threefold, while the length of the ileum (measured at the mesenteric attachment) remains unchanged. The villi become markedly larger and more elongated in the circumferential direction, and have a greater separation between one another. The number of villi per unit surface is markedly reduced but the number of villi per unit length of ileum, whilst appearing to show a small increase, was not significantly altered. The component epithelial cells (absorptive cells) appear unchanged in morphology and size (height). The microvilli of the epithelial cells have the same appearance, size (height) and packing density in the control and the hypertrophic ileum. Glands of Lieberkühn, Peyer's patches and single lymphatic follicles constituting the Peyer's patches are significantly increased in size in the hypertrophic intestine. The serosal surface of the hypertrophic ileum, in spite of the great expansion, remains regularly covered by mesothelial cells; these are much larger than in the controls and have an altered distribution of their microvilli.
Biochemical properties of a keratan sulphate/chondroitin sulphate proteoglycan expressed in primate pluripotent stem cells*
Authors: Cooper Susan , Bennett William , Andrade Jessica , Reubinoff Benjamin E. , Thomson James , Pera Martin F.
Published: March 2003

We previously identified a pericellular matrix keratan sulphate/chondroitin sulphate proteoglycan present on the surface of human embryonal carcinoma stem cells, cells whose differentiation mimics early development. Antibodies reactive with various epitopes on this molecule define a cluster of differentiation markers for primate pluripotent stem cells. We describe the purification of a form of this molecule which is secreted or shed into the culture medium. Biochemical analysis of the secreted form of this molecule shows that the monomeric form, whilst containing keratan sulphate, resembles mucins in its structure and its modification with O‐linked carbohydrate. Immunofluorescence and immunoblotting data show that monkey and human pluripotent stem cells react with antibodies directed against epitopes on either carbohydrate side chains or the protein core of the molecule.
A geometric morphometric study of regional differences in the ontogeny of the modern human facial skeleton†
Authors: Viðarsdóttir Una Strand , O'Higgins Paul , Stringer Chris
Published: March 2003

This study examines interpopulation variations in the facial skeleton of 10 modern human populations and places these in an ontogenetic perspective. It aims to establish the extent to which the distinctive features of adult representatives of these populations are present in the early post natal period and to what extent population differences in ontogenetic scaling and allometric trajectories contribute to distinct facial forms. The analyses utilize configurations of facial landmarks and are carried out using geometric morphometric methods. The results of this study show that modern human populations can be distinguished based on facial shape alone, irrespective of age or sex, indicating the early presence of differences. Additionally, some populations have statistically distinct facial ontogenetic trajectories that lead to the development of further differences later in ontogeny. We conclude that population‐specific facial morphologies develop principally through distinctions in facial shape probably already present at birth and further accentuated and modified to variable degrees during growth. These findings raise interesting questions regarding the plasticity of facial growth patterns in modern humans. Further, they have important implications in relation to the study of growth in the face of fossil hominins and in relation to the possibility of developing effective discriminant functions for the identification of population affinities of immature facial skeletal material. Such tools would be of value in archaeological, forensic and anthropological applications. The findings of this study underline the need to examine more deeply, and in more detail, the ontogenetic basis of other causes of craniometric variation, such as sexual dimorphism and hominin species differentiation.
Vascularization of the developing chick limb bud: role of the TGFβ signalling pathway
Authors: Vargesson Neil
Published: March 2003

The developing vertebrate limb has fascinated developmental biologists and theoreticians for decades as a model system for investigating cell fate, cell signalling and tissue interactions. We are beginning to understand the mechanisms and signalling pathways that control and regulate the outgrowth and formation of the limb bud into a differentiated identifiable limb by late embryogenesis. However, the mechanisms underlying the development and maintenance of the vasculature of the developing limb are far from being completely understood. The vasculature supplies oxygen, nutrients and signals to developing tissues, allowing them to develop and grow. Moreover, a lot of evidence recently points to molecules involved in morphological development also controlling vascular development. Thus understanding how the vasculature forms and is patterned in the developing limb may further our understanding of limb development. In this review I outline how blood vessels are formed and maintained and how the developing chick limb is vascularized. I also review the role of the TGFβ superfamily signalling pathway in the development of the chick limb vasculature: in particular, how antagonizing TGFβ signalling in the developing chick limb has shed new light on the role vascular smooth muscle cells play in vessel calibre control and how this work has added to our understanding of TGFβ superfamily signal transduction.
The formation of skeletal muscle: from somite to limb
Authors: Buckingham Margaret , Bajard Lola , Chang Ted , Daubas Philippe , Hadchouel Juliette , Meilhac Sigolène , Montarras Didier , Rocancourt Didier , Relaix Frédéric
Published: March 2003

During embryogenesis, skeletal muscle forms in the vertebrate limb from progenitor cells originating in the somites. These cells delaminate from the hypaxial edge of the dorsal part of the somite, the dermomyotome, and migrate into the limb bud, where they proliferate, express myogenic determination factors and subsequently differentiate into skeletal muscle. A number of regulatory factors involved in these different steps have been identified. These include Pax3 with its target c‐met, Lbx1 and Mox2 as well as the myogenic determination factors Myf5 and MyoD and factors required for differentiation such as Myogenin, Mrf4 and Mef2 isoforms. Mutants for genes such as Lbx1 and Mox2, expressed uniformly in limb muscle progenitors, reveal unexpected differences between fore and hind limb muscles, also indicated by the differential expression of Tbx genes. As development proceeds, a secondary wave of myogenesis takes place, and, postnatally, satellite cells become located under the basal lamina of adult muscle fibres. Satellite cells are thought to be the progenitor cells for adult muscle regeneration, during which similar genes to those which regulate myogenesis in the embryo also play a role. In particular, Pax3 as well as its orthologue Pax7 are important. The origin of secondary/fetal myoblasts and of adult satellite cells is unclear, as is the relation of the latter to so‐called SP or stem cell populations, or indeed to potential mesangioblast progenitors, present in blood vessels. The oligoclonal origin of postnatal muscles points to a small number of founder cells, whether or not these have additional origins to the progenitor cells of the somite which form the first skeletal muscles, as discussed here for the embryonic limb.
Differentiation, growth and morphogenesis:Acetabulariaas a model system
Authors: VANDEN DRIESSCHE THÉRÈSE , VRIES GHISLAINE M. PETIAU‐DE , GUISSET JEAN‐LUC
Published: March 2003

The aim of this paper is to review the present knowledge of the main aspects of differentiation ofAcetabularia, a unicellular, eukaryotic organism, and to underline the multiple control pathways modulated by circadian rhythmicity. Growth and morphogenesis are sequentially programmed. Timing of cap differentiation is highly dependent on external conditions. The importance of the sequence of processes is shown by experimental disregulation.

The alga is a highly polarized cell, both in morphology and in the relative concentrations of a number of the molecules it contains. Apical cap differentiation is regulated at the post‐transcriptional level and could also depend in part on polyamines and on proteolytic activity.

Acetabulariadisplays a number of circadian rhythms (CR). These rhythms form an elaborate biological time structure (also called temporal morphology, or morphology in time as opposed to morphology in space): the distribution in the 24 h cycle of the peaks and troughs of the oscillating functions. The oscillations display fixed relations both with the other functions and with external conditions (such as the transition from dark to light). Interestingly, the CR modulateAcetabularia'sdevelopment, which is influenced by photoperiod; we present preliminary experiments suggesting that disruption of temporal morphology is deleterious to morphogenesis.

Induction of growth and of morphogenesis are totally dependent on blue light. However, blue light receptors in plants arc probably multiple, but we present arguments suggesting that flavin‐cytochrome b and the associated KHAM‐sensitive molecule are present inAcetabulariaplasma membrane and are involved in blue light perception. Agents interfering with different steps of signal perception and transduction show that at least some of these steps are temporally regulated. According to recent experiments from our laboratory, the existence of a redox signalling mechanism appears to be highly probable.

The phytohormones (or plant regulators), auxin (indole acetic acid), abscisic acid and ethylene, exert cell‐regulatory functions and are involved inAcetabulariadifferentiation. They also modulate at least some circadian rhythms. Finally, circadian rhythms intervene in differentiation and are proposed to have an integrative function.

CONTENTSSummary1I.Introduction: the cell cycle and morphology ofAcetabularia2II.Growth and cap morphogenesis: the developmental programme3III.Polarity5IV.Temporal morphology6V.Induction of growth and cap morphogenesis9VI.The plasma membrane12VII.Hormones: development and metabolic activity inAcetabularia12VIII.Phytohormones receptors and insulin receptors15IX.Other possible hormones16X.Fundamental role of CR: their intervention in modulating multiple steps in differentiation16XI.Conclusions and perspectives17Acknowledgements17References17
Mechanical impedance of root growth directly reduces leaf elongation rates of cereals
Authors: YOUNG I. M. , MONTAGU K. , CONROY J. , BENGOUGH A. G.
Published: March 2003

A dry soil is generally a hard soil. Thus, the effects of water stress and mechanical impedance on plant growth are difficult to separate. To achieve this we have developed a growth cell that allows manipulation of the strength of growth media (i.e. mechanical impedance) without altering the availability of water or nutrients. We monitored leaf elongation rates of barley and wheat seedlings before and after the mechanical impedance to root growth was increased. Results show that a large and rapid reduction (within 10 min) of leaf elongation rates occurred after impedance to the roots was increased. The average reductions for barley and wheat, with associated standard errors, were 22.6 % (4.84) and 36.2% (5.48), respectively. The data are consistent with the hypothesis that mechanical impedance of roots might have a direct negative effect on leaf growth even where nutrients and water are in plentiful supply to the plant. The implications of the rate of the response are examined with respect to the underlying mechanisms controlling root‐shoot signalling.
Ozone uptake inPrunus serotina, Acer rubrumandQuercus rubraforest trees of different sizes
Authors: SAMUELSON L. J. , KELLY J. M.
Published: March 2003

Information on ozone uptake by various tree species has been derived mainly from controlled‐exposure studies of seedlings. Parallel measurements of foliar physiological processes in large trees are rare, as are measurements of local ozone concentrations within forest environments. Thus, our objectives were to characterize foliar ozone uptake in forest trees of different size and to identify a mechanistic linkage between small and large trees. Light‐saturated net photosynthesis (Pn), stomatal conductance (gH2O), and ozone uptake (gO23) in seedling (< 2 m), sapling (2–5 m) and mature (9–21 m) black cherry (Prunus serotinaEhrh.), northern red oak (Quercus rubraL.) and red maple (Acer rubrumL.) trees were measured monthly over two growing seasons at sites at high (1240 m) and low (600 m) elevation in the Great Smoky Mountains National Park. Seasonal ozone dose to northern red oak and red maple in the upper crown of mature trees was approx. double that of respective understorey seedlings and saplings. Seasonal ozone dose to black cherry was up to six times greater in mature trees than in seedlings and saplings. The lower ozone dose to understorey trees was mainly a function of lower gH2o, although canopy gradients in ozone concentration were indicated. Differences inPnandgH2O between small and large deciduous forest trees were linked to variation in nitrogen concentration expressed on a leaf area basis.
Biological control of pathozone behaviour and disease dynamics of Rhizoctonia solani by Trichoderma viride
Authors: BAILEY D. J. , GILLIGAN C. A.
Published: March 2003

This paper presents and tests a method to scale up from the dynamics of infection and disease on single plants in order to predict the behaviour of epidemics in populations of plants, in the presence of a biological control agent. Specifically, we quantify the effect of the antagonistic fungus, Trichoderma viride, Pers ex. Gray, on the pathozone dynamics of the damping‐off fungus, Rhizoctonia solani Kühn on radish. The results from these individual‐based experiments are used to predict the progress of an epidemic and the results are compared with experimental epidemics in microcosms. The addition of T. viride close to a germinating radish plant reduced the extent of the pathozone influence from 22.6 to 13.8 mm. Trichoderma viride also inhibited the evolution of infection efficiency of R. solani. The evolution of infection efficiency over time is described by a simple non‐linear model for the probability of infection with distance, in which certain of the parameters vary with time. By combining this with a model based on conditional probabilities for the location and infectivity of randomly dispersed propagules within the pathozone, we were able to scale up and predict the disease progress of R. solani in a population of radish plants, and the extent of control effected by T. viride. Disease progress rose progressively to a maximum of 42 % diseased plants in the unprotected crop compared with a sigmoidal approach to 13 % in the protected crop. We show that these properties are consistent with a monomolecular function for primary infection with a temporally‐varying rate parameter. We also show that the central region of the pathozone, where the joint probabilities of occurrence of a randomly located propagule and its ability to infect are maximal, has a large influence on the sensitivity of epidemics to pathozone dynamics. This is an important example of interpreting population behaviour of an epidemic from the infection and disease of single plants.
Structural diversity in (vesicular)–arbuscular mycorrhizal symbioses
Authors: SMITH F. A. , SMITH S. E.
Published: March 2003

summary

This review describes diversity in the structure of (vesicular)‐arbuscutar (VA) mycorrhizas, i.e. endomycorrhizas formed by Glomalean fungi. In particular, we consider the extent in the plant kingdom of the two classes first described by Gallaud (1905). These are: (1) the Arum‐type, defined on the basis of an extensive intercellular phase of hyphai growth in the root cortex and development of terminal arbuscules on intracellular hyphai branches; (2) the Paris‐type, defined by the absence of the intercellular phase and presence of extensive intracellular hyphai coils. Arbuscules are intercalary structures on the coils. However, there have been many reports that in Paris‐types arbuscules are relatively few in numbers, small, or absent altogether.

A survey of the literature has revealed that Paris‐types occur more frequently in the plant kingdom than Arum‐types and predominate in ferns, gymnosperms and many wild angiosperms. The cultivated herbs that are the subject of much experimental work are mostly Arum‐types. Although evidence is still limited, there are differences at the family level. In 41 angiosperm families there are records of only Poris‐type VA mycorrhizas and in 30 families records of only Arum‐types. Another 21 families have examples of both classes, or intermediates between them. Accordingly, we consider whether the original division into two classes is still useful. We conclude that it is when considering the physiology of the symbiosis and especially the issue of whether different fungus/host interfaces have specialized roles in transfer of inorganic nutrients and organic carbon between the partners, if there is no such specialization between hyphai coils and arbuscules, then the latter might not be necessary1 for the function of Paris‐types. This would account for reports of the infrequency or absence of arbuscules in this class. The control exerted on structures by the genomes of host and fungus, and possible reasons (anatomical and physiological) for the existence of the VA mycorrhizal structures, are discussed. The presence or absence of extensive intercellular spaces and differences in the wall structure of cortical cells might be particularly important in determining which type of VA mycorrhiza is formed.

CONTENTS

Summary
373

I.
Introduction: Arum‐types and Pom‐types
374

II.
Possible functional implications
375

III.
Extent of the two classes in the plant kingdom
377

IV.
Is the distinction between classes useful?
383

V.
The structural basis
383

VI.
The role of the fungal genome
384

VII.
Physiology revisited
384

VIII.
Conclusions
385

Acknowledgements
386

References
386
Surface tension and viscosity of axenic maize and lupin root mucilages
Authors: READ D. B. , GREGORY P. J.
Published: March 2003

summary

In many plants, mucilage permeates the interface between root and soil, yet little is known about its physical properties or its influence on the physical properties of the rhizoasphere. Mucilage was collected from 3–4‐d‐old, axenically‐grown maize (Zea mays L. cv. Freya) and lupin (Lupinus angustifolius L. cv. Merrit) seedlings. Surface tension and viscosity were measured over a range of mucilage hydration, and neutral sugar analyses of the hydrolysed mucilages were obtained by gas chromatography. Surface tension of both maize and lupin mucilage was reduced to ∼ 48 mN m−1 at total solute concentrations > 0.7 mg ml−1, indicating the presence of powerful surfactants. Mucilage viscosity increased with increasing solute concentration and decreasing temperature. At a total solute concentration of 0.7 mg ml−1, the viscosity of maize mucilage at 20 °C was 2.1 mPa s (approx. double that of pure water), increasing to 3.3 mPa s at 5 °C. Both maize and lupin mucilage showed viscoelastic behaviour. The major component of maize mucilage was found to be glucose, but in lupin it was fucose.

The surface tension and viscosity results support the idea that mucilage plays a major role in the maintenance of root‐soil contact in drying soils. As surface tension decreases, the ability of the mucilage to wet the surrounding soil particles becomes greater. Also, as viscosity and elasticity increase, the resistance to movement of any soil particles in contact with the mucilage increases, a degree of stabilization of the rhizosphere structure is achieved and hydraulic continuity is maintained. It is unclear whether the surfactant is actively secreted by the root or is present simply as a result of leakage from root cells.
An image‐analysis technique for accurate counting of pollen on stigmas
Authors: BECHAR A. , GAN‐MOR S. , VAKNIN Y. , SHMULEVICH I. , RONEN B. , EISIKOWITCH D.
Published: March 2003

summary

Pollen counting is an important element of research in pollination, and the majority of current methods involve manual counting. An image‐processing technique has been developed for accurate counting and sizing of small particles, and this was tested on almond pollen grains. Our automatic process was found to be several times faster than manual counting and more accurate, with an average error of only 3 %. Because of its simplicity, it is an attractive tool for research on such topics as pollen viability or germination. It was found that in the methods using vials there were ‘residues’ of c. 17 % on the vial walls and on the handling tools. In addition, the first drop from each vial contained, on average, 1–65 times more grains than the average number of grains in all drops, whereas the last drop from each vial contained fewer grains than the average. This phenomenon was correlated with the non‐uniform pollen distribution in the suspension. An automatic counting system is therefore, recommended, to avoid the problem, otherwise a calibration procedure should be used that accounts for both the residues on the tools and the non‐uniformity of contents of sample drops.
Effects of low ozone exposure of spring wheat on net CO2 uptake, Rubisco, leaf senescence and grain filling
Authors: OJANPERÄ KATINKA , PÄTSIKKÄ EIJA , YLÄRANTA TOIVO
Published: March 2003

Effects of ozone on spring wheat (Triticum aestivum L. cv. Satu) were studied in an open‐top chamber experiment during two growing seasons (1992–1993) at Jokioinen in south‐west Finland. The wheat was exposed to filtered air (CF), non‐filtered air (NF), non‐filtered air+35 nl l−1 ozone for 8 h d−1 (NF+) and ambient air (AA). Each treatment was replicated five times. Two wk after anthesis, after 4 wk of ozone treatment (NF+, 45 nl l−1 1000–1800 hours, seasonal mean) the net CO2 uptake of wheat flag leaves was decreased by c. 40% relative to CF and NF treatments, both initial and total activity of Rubisco and the quantity of protein‐bound SH groups were decreased significantly. Added ozone also significantly accelerated flag leaf senescence recorded as a decrease in chloroplast size. The effect was significant 2 wk after anthesis, and senescence was complete after 4 wk. In the CF and NF treatments senescence was complete 5 wk after anthesis. The significant effect of ozone on the chloroplasts and net CO2 uptake 2 wk after anthesis did not affect the grain filling rate. However, since the grain filling period was shorter for ozone fumigated plants, kernels were smaller. The decrease in 1000‐grain weight explained most of the yield reduction in the plants under NF+ treatment. The results indicate that wheat plants are well buffered against substantial decrease in source activity, and that shortened flag leaf duration is the major factor causing ozone‐induced yield loss.
Foliar application of nitrate or ammonium as sole nitrogen supply in Ricinus communis I. Carbon and nitrogen uptake and inflows.
Authors: PEUKE ANDREAS D. , JESCHKE W. DIETER , DIETZ KARL‐JOSEF , SCHREIBER LUKAS , HARTUNG WOLFRAM
Published: March 2003

Following a precultivation with pedospheric nitrogen nutrition, nitrate or ammonium solutions were supplied to the shoots of Ricinus plants by spraying (during the experimental period) resulting in an increase of biotic/organic and abiotic/inorganic particles on the surface, which significantly increased wetting of the leaf surfaces. The distribution of particles on the surface of sprayed leaves, in particular crystals around and in stomata, indicated the possible entry of nutrients via thin water films through the stomatal pores in addition to diffusion through the cuticle. Ammonium was taken up more readily than nitrate by the foliage, but both at relatively low rates which caused N limitation. Interestingly, the inorganic N, both in the form of nitrate and even ammonium, was entirely assimilated in the shoots; phloem transport of inorganic N to the root was negligible. The flows of malate, and the acidification of the apoplastic washing solution of leaves in ammonium‐sprayed plants pointed to the role of metabolism of malate and excretion of protons in maintaining pH during ammonium assimilation in the shoot. Ammonium‐sprayed plants incorporated the N in the same amounts in shoots and roots, only 38% of the shoot‐borne N being recycled in the xylem. In nitrate‐sprayed plants the root was not only favoured in N partitioning, but even a net export of previously incorporated N from the shoots occurred which reflected the N limitation. The N limitation also affected carbon metabolism, in particular the flows of C, incorporation in the shoot and photosynthesis, which were decreased when compared with data from recent experiments with pedospheric well fed Ricinus. However, there was little difference in C flows between nitrate and ammonium‐sprayed plants with respect to respiration, C partitioning and, most interestingly, in relative stimulation of root growth. The loss of C from dark respiration of the shoots was high on a f. wt basis as well as in relative terms, owing to exclusive N assimilation in the shoot. In general the plants invested untargeted increases in root growth as a result of N limitation irrespective of the imposed artificial treatment which made the shoot the site of mineral N uptake.
Ecophysiology of salt excretion in the xero‐halophyte Reaumuria hirtella
Authors: RAMADAN T.
Published: March 2003

Different aspects of salt excretion from leaves of the xero‐halophyte Reaumuria hirtella Jaub. et Sp. (Tamaricaceae) were investigated under the extremely arid conditions of the desert. The diurnal excretion pattern, which gradually decreased toward midday, showed a negative correlation with the daily transpiration pattern. The relative excretion, which is the ratio between the absolute excretion of Na+ and the change in its internal content, was maximal at sites with low salinity, and decreased when the concentration of NaCl in the root environment increased. By contrast, the absolute excretion increased from 253 to 323 mmol Na+ g−1 f. wt per 12 h with increase in the total soil salinity from 0·24 to 1·23%, respectively. Water stress conditions, caused either by increasing soil salinity or by dryness of the atmosphere, greatly influenced the efficiency of excretion process.

Six ions: Na+, K+, Ca2+, Mg2+, Cl− and SO42− constituted 96·8% of the d. wt of the field‐collected secreted salts. Na+ and Cl−, which were the predominating ions in the soil solution of the root environment, were also the predominantly secreted, constituting c. 89% of salts secreted. The proportion of Na+ which was prevented from entry into the roots increased with increasing Na+ concentration in the soil solution. More than 67% of the absorbed NaCl was secreted by leaves during the day. However, the accumulated salts contributed to the osmotic potential (ψs) and improved the plant water status. The osmotic potential of the plant sap at the end of the day or during periods of low excretion rates was shown to be decreased −7·3 to −13·7 bar from that in the morning. The fraction of osmotic potential decreased during the day (Δψs) was positively correlated with the soil salinity. These retained salts are expelled from the leaves by increased efficiency of extraction during the night and early morning, so that the plant begins the day with low internal salt content, and the leaf reservoirs become suitable for a new supply. The rejection mechanism at the plant roots and the secretion mechanism at shoots allow the plant to maintain its internal salt content at an approximately constant level despite the great variation in soil salinity.
Corner's rules revisited: ontogenetic and interspecific patterns in leaf–stem allometry
Authors: BROUAT C. , GIBERNAU M. , AMSELLEM L. , McKEY D.
Published: March 2003

We studied interspecific and ontogenetic relationships between the size of a leaf and the primary diameter of the internode bearing it. Although these two variables are known to be strongly correlated across species, the form of this relationship has not been studied. In a re‐analysis of published data on interspecific comparisons of 69 temperate tree species, we showed the existence of a strong relationship between twig cross‐sectional area (before secondary growth) and surface area of leaves borne by it, within each of three morphological groups, deciduous angiosperms, evergreen angiosperms, and gymnosperms. Within each of these groups, this relationship is isometric: across species, primary cross‐sectional area of the stem increases proportionally with leaf surface area. When we consider the relationship between the cross‐sectional area of a twig and the surface area of one leaf borne by it, the y‐intercepts for this relation are different for the three groups. However, when total leaf surface area per first‐year shoot is considered, no differences remained between gymnosperms and evergreen angiosperms, but deciduous angiosperms continued to be distinct. This difference between deciduous and evergreen groups could be due to differences in leaf volume (evergreen species have thicker leaves than deciduous) or in traits related to a trade‐off between life span of leaves and their physiological behaviour.

We present results of the first quantitative study of the relationship between leaf size and primary diameter of the stem during ontogeny. Both these parameters increase during development of the plant from seedling to adult. For the four tree species examined, the relationship between primary cross‐sectional area of the stem and leaf surface area is also isometric.

These results bear on a functional interpretation of the relationship between leaf and stem dimensions, suggesting that vascular supply is directly proportional to the requirements of leaves supported by the stem.
Root proliferation, soil fauna and plant nitrogen capture from nutrient‐rich patches in soil
Authors: HODGE A. , STEWART J. , ROBINSON D. , GRIFFITHS B. S. , FITTER A. H.
Published: March 2003

We investigated interactions between plant roots, protozoa and nematodes after addition of patches containing inorganic or organic nitrogen in order to determine whether root proliferation could explain the capture of N by the plant from the patch. Decomposition of a 15N/13C, dual‐labelled, organic patch in the absence of plant roots was also examined. In the decomposing patch the amounts of 13C and 15N remaining co‐varied and both declined with time. Nematode numbers increased. However, protozoan biomass and inorganic N (NO3− and NH4+) availability did not significantly alter as decomposition of the patch progressed. Addition of inorganic N patches, as NH4NO3 solutions, to the first lateral to emerge from the main seminal root axis of Lolium perenne L. seedlings had no effect on root growth compared with controls 16 d after addition. Protozoan biomass increased. Furthermore, log protozoan biomass and NO3− concentrations of the growth medium were significantly (P<0·05) and positively related. Plant response (i.e. biomass production, N capture and root length) to an added organic patch was examined using five different grass species (Festuca arundinacea L., Phleum pratense L., Poa pratensis L., Dactylis glomerata L. and L. perenne). Total plant biomass was significantly (P<0·05) repressed by an organic patch. Plant N content was reduced when an organic patch was present but N concentrations were greater. Roots were generally slow to proliferate within the patch but there was a significant (P<0·05) species×patch interaction for root length within the patch at harvest and in the 2‐cm band below it. However, 15N capture by the plants was not related to mean root length duration. All species captured similar amounts of 15N (c. 3–5%) at harvest as a percentage of the initial 15N added in the organic patch. Similarly, the percentage of the total N captured from the patch was not related to the proportion of the root weight within the patch. The fraction of the captured N from the organic patch as a percentage of the plants' total N, however, did differ among species. Substantial amounts (>62%) of the 15N initially added remained in the patch at harvest. Much less (c. 13–21%) 13C remained in the patch. Protozoan biomass and nematode numbers increased significantly (P<0·05) in the organic patch, although the relationship between the two groups was not significant. As in the inorganic N study, the relationship between log protozoan biomass and NO3− concentrations in the soil was significantly positive. We conclude that, when grown in monoculture, plants' N capture from an organic patch is not a simple function of root proliferation. External factors, not plant attributes, are more important in controlling patch exploitation.
Editorial
Authors: AYRES P. G.
Published: March 2003

Membership of our Board of Advisors to the Editors has remained almost static since the Board was founded in 1995, but significant turnover begins this summer. Accordingly, I offer a warm welcome to new members of the Board and thank those who have agreed to extend their membership. I thank especially those leaving the Board for their invaluable support during the first three years of its life. The workplaces and interests of Board members reflect both the international base of the New Phytologist and the wide range of subjects that it regularly publishes. SCI ratings support the belief that the New Phytologist is the world's leading broad‐spectrum botanical journal. Given that breadth of subject matter, it is all the more remarkable that the journal has a high Impact Factor, 2·2.

The good health of the New Phytologist, and the charitable Trust that owns it, is further indicated by recent expansion of our activities. For each of the last three years, symposia, to which numerous distinguished international speakers contributed, have been organized in the UK. Proceedings have been published in the journal but they have also been made available for purchase as attractively bound separates, the most recent being Major Biological Issues Resulting from Anthropogenic Disturbance of the Nitrogen Cycle (eds. T. A. Mansfield, L. Sheppard and K. W. T. Goulding). This year, the symposium will be held in Montpellier, France, on the subject The Gap between Isolated Plants and Growing Canopies, while in 1999 it will move to the USA. In response to numerous requests, particularly from university teachers, we are now collecting recent Tansley Reviews around themes and publishing these too as separates. The first collection, Leaf Development and Function, is now available.

Like many forward looking journals, the New Phytologist is fully online (at http://www.journals.cup.org): unlike that of many other journals, our online version was launched free of charge to subscribers. This is just one of the many ways in which this independent journal can help botany and botanists. Indeed, monies from the Trust support a range of activities that promote botany (see volume 134, facing p. 197 for details). The journal will be 100 years old in 2002. The Trustees would be especially pleased to receive requests for support for activities that would mark the centenary.

As I noted in my previous Editorial, three years ago, Independent and International remain our key words.
Effects of inorganic nitrogen compounds on the activity and synthesis of nitrogenase in Gloeothece (Nägeli) sp. ATCC 27152
Authors: CHENG J. , HIPKIN C. R. , GALLON J. R.
Published: March 2003

Addition of 2 mM nitrite or ammonium to aerobically incubated cultures of Gloeothece rapidly inhibited N2 fixation (measured as acetylene reduction). In contrast, 2 mM nitrate inhibited N2 fixation less rapidly and less extensively, and often temporarily stimulated nitrogenase activity. The inhibitory effects of both nitrate and ammonium could be prevented by addition of 3 mM L‐methionine‐DL‐sulphoximine, suggesting that the true inhibitor of N2 fixation was an assimilatory product of ammonium rather than either ammonium or nitrate itself. The inhibition of N2 fixation by nitrite could not, however, be prevented by addition of L‐methionine‐DL‐
sulphoximine. On the other hand, nitrite (unlike nitrate and ammonium) did not inhibit N2 fixation in cultures incubated under a gas phase lacking oxygen. These findings suggest that the mechanism whereby nitrite inhibits N2 fixation in Gloeothece differs from that of either nitrate or ammonium. The inhibitory effect of nitrite on N2 fixation did not involve reduction of nitrite to nitric oxide, though nitric oxide was a potent inhibitor of nitrogenase activity in Gloeothece. Nitrate and nitrite inhibited the synthesis of nitrogenase in Gloeothece, while ammonium not only inhibited nitrogenase synthesis but also stimulated degradation of the enzyme. In addition, all three compounds favoured the appearance of the Fe‐protein of nitrogenase in its larger, presumed inactive, form.
Responses to flooding intensity in Leontodon taraxacoides
Authors: GRIMOLDI A. A. , INSAUSTI P. , ROITMAN G. G. , SORIANO A.
Published: March 2003

Natural flooding is one of the major factors affecting vegetation dynamics in many regions of the world. The Flooding Pampa Grasslands (Argentina) are frequently exposed to flooding events of diverse intensity and duration, some of which Leontodon taraxacoides, an exotic dicot. frequent in these grasslands, seems to survive. Its responses to four different water depths (0, 1, 7 and 13 cm) were studied. The results indicate that plants in conditions of total submergence (depth of 13 cm) did not survive. In less severe flood conditions, increases in the leaf insertion angle resulted in the maintenance of a large proportion of the total leaf area above the water. Differences in leaf length and a decrease in the width and the proportion of lobes per leaf were also found under partial submergence conditions (depth of 7 cm). Root and leaf aerenchyma, present in unflooded plants, showed a significant increase in flood conditions. In spite of the anatomical and morphological responses, total biomass and leaf area were severely affected by water depth. Control plants allocated more biomass to reproductive organs, while partly submerged plants allocated more to leaves and less to reproductive organs. Mature L. taraxacoides plants presented a wide range of plastic adjustment as a survival strategy in soil anaerobiosis, and appear to be able to survive short spring floods in a vegetative state; in contrast, they might not tolerate total submergence conditions imposed by more intense and long‐lasting floods.
Multistrain infections of the grass Brachypodium sylvaticum by its fungal endophyte Epichloë sylvatica
Authors: MEIJER GERT , LEUCHTMANN ADRIAN
Published: March 2003

Endophytes of the genus Epichloë (Clavicipitaceae, Ascomycota) are systemic symbionts of cool‐season grasses. Their interactions with grass hosts may vary between mutualistic and pathogenic depending on the mode of endophyte reproduction. Sexual strains prevent flowering and seed set (choke disease) of the host and can be horizontally transmitted by ascospores, while asexual strains remain asymptomatic and are vertically transmitted through seeds. In Switzerland nearly all plants of Brachypodium sylvaticum (Huds.) P.B. are infected by Epichloë sylvatica Leuchtmann & Schardl, but choke symptoms are formed very rarely, and are restricted to particular locations and to a minority of plants at those locations. Earlier research has revealed that E. sylvatica is genetically differentiated into sexual and asexual subpopulations. Given the high level of infection and assuming horizontal transmission of sexual strains, multiple host infections have been predicted. In this study, 25 plants out of 63 examined by isozyme analysis were found to be infected by two or three different endophyte genotypes. In most cases endophyte genotypes appeared to be correlated with the symptom type of a particular tiller, suggesting that the fungal genome controls choke formation and that the sexual and asexual subpopulations are separated at the ramet (tiller) level rather than at the genet (plant) level. These conclusions were further supported by analyses with log‐linear models of the population structure of E. sylvatica at four locations where choke symptoms were present. These analyses also revealed a geographic structure in the asexual subpopulation but not in the sexual subpopulation which could be caused by the different dispersal ranges of their propagules. The rare occurrence of sexually reproducing strains and the dominance of a single genotype in asymptomatic plant populations may be explained by the colonization history of B. sylvaticum and its endophyte in Switzerland.