bluuebunny/crossref_metadata_2025 huggingface dataset:
Ozone effects on root‐disease susceptibility and defence responses in mycorrhizal and non‐mycorrhizal seedlings of Scots pine (Pinus sylvestris L.)
Authors: BONELLO PIERLUIGI , HELLER WERNER , SANDERMANN HEINRICH
Published: April 2006

Interactions between ozone and biotic stress caused by a pathogen, Heterobasidion annosum (Fr.) Bref., in mycorrhizal [Hegeloma crustuliniforme (Bull, ex St. Am.) Quel.] and non‐mycorrhizal Scots pine seedlings were investigated using a semi‐axenic model system.

Ozone exposure (200 nl 1−1, 8 h d−1 for 28 d) increased disease incidence significantly, but mycorrhizal infection completely prevented this negative effect. The presence of the pathogen on the root systems was necessary for the induction of changes in the soluble and wall‐bound secondary compounds of roots and needles; ozone alone did not induce such changes. Mycorrhizal infection appeared to have a dampening effect on the induction of these compounds.

H. annosum induced a significant accumulation of the two pine stilbenes both locally and systemically in the more susceptible seedlings. In these seedlings ozone had a significant positive effect on the accumulation of both stilbenes in the roots, but it reduced pinosylvin and had no effect on pinosylvin 3‐methyl ether in the needles. The catechin content of the roots decreased in the same infected seedlings, but to a larger degree upon ozone treatment. One compound of as yet unknown structure accumulated gradually in the infected roots over the experimental period, and could thus be associated with resistance. Its accumulation was little affected by ozone treatment. Among the root cell wall‐bound phenolics analyzed, only lignin‐like material showed significant changes. The presence of the pathogen was again necessary for induction, but ozone had an inhibitory effect on this response.

Pure pinosylvin applied through the hypocotyls of excised seedlings was shown to be phytotoxic, with the needles displaying discoloration and wilting as observed after pathogenic inoculation, and being characterized by a lower chlorophyll content and increased transpiration. Accumulation of pinosylvin in the needles was detected at amounts comparable to those found in the main experiment.
Nitrogen relations of the sorghum‐Striga hermonthica host‐parasite association: germination, attachment and early growth
Authors: CECHIN I. , PRESS M. C.
Published: April 2006

The probability of the parasitic angiosperm Striga hermonthica achieving a successful union with its sorghum host is in part dependent on the concentration of ammonium nitrate in the growth medium. Germination rates were higher with 1 mM than with 3 mM ammonium nitrate. Ammonium nitrate did not influence either the stability of active components of host root exudate, or their perception by the parasite's seed. High concentrations of ammonium nitrate did not significantly reduce the leakage of potassium ions from sorghum roots (although patterns of exudation may differ between groups of compounds). Thus, it appears that ammonium nitrate reduced either the production of stimulatory compounds, or their specific leakage from host roots. Subsequent attachment of the parasite radicle and early growth of the plant were also lower at higher concentration of ammonium nitrate, and possible reasons for these observations are discussed.
Responses to salinity of grapevine plants with split root systems
Authors: SHANI U. , WAISEL Y. , ESHEL A. , XUE S. , ZIV G.
Published: April 2006

Grape yield, shoot and root vigour and water use by grapevine plants with split root systems were investigated. Some plants had both root parts continuously irrigated either with fresh or with saline water. Some plants got a dual treatment; one portion got fresh water and the other saline water. The irrigation water of a third group was changed during the experiment from fresh to saline water or vice versa.

Fruit yield and root and shoot viability were positively correlated with the actual water use.

Water ascent along the stem of the grapevines was found to be sectorial. Most of the water was supplied by the freshwater roots. Only small quantities of water were supplied by salt‐affected roots to their respective twigs.

Changes in the water quality of the root medium induced a dual effect: (a) a fast response, caused by the direct change in the ambient w7ater potential; and (b) a long‐term response that developed over several weeks. The latter response was induced by the development of new roots, or by death of others, upon a change in the quality of the irrigation water.

The commonly used grapevine plants of the Arava valley are negatively affected by NaCl already at concentrations below 100 mM. Under such conditions, shoot growth and fruit yield were seriously inhibited, even when one part only of the root system was exposed to saline water.
The functional ecology of Empodisma minus (Hook, f.) Johnson & Cutler in New Zealand ombrotrophic mires
Authors: AGNEW A. D. Q. , RAPSON G. L. , SYKES M. T. , BASTOW WILSON J.
Published: April 2006

Mires dominated by restionaceous rushes occur in valley and basin sites around New Zealand. The main restiad species is Empodisma minus which produces a surface mat of negative geotropic roots which eventually form a principal part of the underlying peat. Comparison of the peat chemistry of four such mires with a minerotrophic mire w*as consistent with their suspected ombrotrophic status. The base‐exchange capacity achieved (704 + 23.3 mequiv m−2 of the surface) by the superficial roots of Empodisma is at least as great as that of the New Zealand Sphagnum cristatum which is not dominant in ombrotrophic conditions. The widespread development of a hummock and hollow microtopography may be associated with higher rainfall regimes and the propensity of Empodisma for directing most incoming rainfall (on which its nutrient economy depends) down its wiry stems.
Gene expression under temperature stress*
Authors: HOWARTH CATHERINE J. , OUGHAM HELEN J.
Published: April 2006

In this review, changes in plant gene expression in response to environmental stresses are discussed using the examples of high and low temperature treatments. While some changes may contribute to acclimatory processes which improve plant survival or performance under stress, others may be ‘shock’ responses indicative of sensitivity. The heat‐shock response, which is almost ubiquitous among eukaryotic organisms, is characterized by repression of normal cellular protein synthesis mediated at both the transcriptional and the translational level, and induction of heat‐shock protein (HSP) synthesis. There is a correlation between HSP synthesis and induced thermotolerance in plants, but the evidence for a causal relationship is not conclusive. The possible biochemical functions of some of the HSPs are now becoming apparent; they are believed to play an important role in preventing accumulation of damaged proteins in the cell during heat shock. Although no other environmental stress elicits the full heat‐shock response, certain treatments do induce synthesis of subsets of the HSPs, and the reasons for this are considered. Alterations in gene expression in response to low temperatures are more diverse and usually less dramatic than the heat‐shock response, with which they share little, if any, homology. Biochemical adjustments during cold treatment are discussed, with particular reference to those which contribute to acclimation. Several genes whose expression is induced by cold have been cloned and characterized, and in some cases it is possible to attributein vivofunctions to them; they include enzymes of lipid, carbohydrate and protein metabolism, structural proteins and putative cryoprotectants. The use of transgenic plants is further facilitating an investigation of the biochemical factors which are important in cold acclimation. Drought, osmotic stress and abscisic acid induce expression of many of the same genes as does cold treatment; it seems likely that some of the products of these genes contribute to increased freezing tolerance by protecting against intracellular dehydration.

ContentsSummary1I.Introduction1II.High temperature stress3III.Low temperature stress10IV.Concluding remarks20Acknowledgements21References21
Flooding resistance and shoot elongation in relation to developmental stage and environmental conditions in Rumex maritimus L. and Rumex palustris Sm.
Authors: Van der SMAN A. J. M. , BLOM C. W. P. M. , BARENDSE G. W. M.
Published: April 2006

The flooding resistance of Rumex maritimus L. and Rumex palustris Sm., two species from frequently flooded areas of river forelands, was studied in two large‐scale outdoor experiments. Plants were raised in cohorts and in several stages of development subjected to four weeks of submergence in early summer or in midsummer.

The role of under‐water shoot elongation in raising foliage above the water line was not equally important in both species. In R. maritimus, survival following either early‐ or midsummer flooding was restricted mainly to plants which emerged from the water surface by elongating their main shoot. R. palustris was better able to survive submergence, especially under early‐summer conditions.

As a consequence of survival being restricted to plants in the stem elongation stage, flooded plants of R. maritimus all reproduced in the first growing season and seed output correlated positively with stem length immediately after flooding. This was also the case for R. palustris flooded at midsummer. However, for plants of R. palustris which were flooded in early summer and remained below the water line, flowering was delayed or even postponed to the following season.

Variation in seed weight was much larger in R. maritimus than in R. palustris and more clearly related to cohort and treatment effects.

Differences between both species in Hooding resistance did not seem to be primarily caused by different abilities of shoot elongation, but by differences in submergence tolerance in relation to life‐history characteristics.
H+ exchange and nutrient uptake by roots of the emergent hydrophytes, Cyperus involucratus Rottb., Eleocharis sphacelata R. Br. and Juncus ingens N. A. Wakef.
Authors: SORRELL BRIAN K. , ORR PHILIP T.
Published: April 2006

We immersed the root systems of three emergent aquatic monocots (Cyperus involucratus Rottb., Eleocharis sphacelata R. Br. (both Cyperaceae), and Juncus ingens N. A. Wakef. (Juncaceae)) in nutrient agar gels with pH indicators and pH microelectrodes to study H+ exchange by root systems. For all three species, the pH changed at the tips of the adventitious roots and around young laterals. Older, lignified surfaces had little effect on pH. The pH changes around the laterals were affected by the form of nitrogen in the nutrient gel When NO3− was supplied as the N source, there was a small pH increase, whereas NH4+ enhanced H+ release, causing the pH adjacent to the laterals to decrease below 4.5. In contrast, root tips acidified the media, irrespective of the nutrient composition. H+ exchange was quantified from titrimetric assays of H+ exchange in nutrient solutions. There was a net H+ efflux from the roots of all three species into complete nutrient solutions with NH4+ as the N source, ranging from 246 μmol H+ h−1 g−1 d. wt for C. involucratus, to 32 μmol H+ h−1 g−1 d. wt for J. ingens. The H+ efflux into similar nutrient solutions with NO3− as the N source ranged from −89 μmol H+ h−1 g−1 d. wt for C. involucratus to −0.8μmol H+ h−1 d. wt for J. ingens. By assuming that H+ exchange was mainly located in the laterals, rates of H+ excretion as high as 542 μmol H+ h−1 g−1 d. wt can be calculated for C. involucratus in NH4+ solutions. Rates of H+ excretion by C. involucratus were scarcely affected by solutions of most Other ions. The NH4+‐induced H+ release was dramatically reduced by H+ pump inhibitors, attaining only 18% of control rates with 50 μM diethylstilbestrol and 38% of control rates with 5 μM dicyclohexylcarbodiimide.
Xylem development in relation to water uptake by roots of grapevine (Vitis vinifera L.)
Authors: MAPFUMO E. , ASPINALL D. , HANCOCK T. , SEDGLEY M.
Published: April 2006

Axial resistance (Ra) was estimated from xylem diameter measurements obtained from periodic acid and toluidinc blue O (PAS‐TBO) stained sections of Vitis vinifera L. ev. Shiraz. Multiple linear regression showed a strong negative relationship between axial resistance and either root diameter or distance from the root tip. Water stress treatments did not affect the relationships, but plant age significantly influenced the intercept of the regression. The use of both lignin and cytoplasm stain showed that some vessels retained degenerating protoplasm which would impede water flow. Inclusion of these vessels in calculations of axial resistance could account for the underestimation reported by some authors in comparison with experimental determinations. Calculations based on the assumption that all xylem vessels, large and small, are involved in axial water conduction showed that use of mean xylem diameter might result in overestimating values by a magnitude of between 1.7 and 4.4. The use of individual xylem vessel diameters gave more accurate estimation of axial resistance. Some adjacent secondary xylem and metaxylem vessels were observed to merge into single vessels as a result of breakdown of the wall between them. Implications of such a developmental phenomenon are discussed.
Photosynthesis and nutrient supply in needles of Sitka spruce [Picea sitchensis (Bong.) Carr.]
Authors: CHANDLER J. W. , DALE J. E.
Published: April 2006

Growth and photosynthetic development were measured for currently developing needles of young trees of Sitka spruce [Picea sitchensis (Bong.) Carr.] throughout their fourth growth season. Treatments included trees that were fully fertilized (control), trees deficient in phosphorus (–P), or nitrogen (–N), and trees initially deficient but then supplied with phosphorus (–PR) or nitrogen (–NR). Growth was measured in terms of needle projected area, and the photosynthetic components measured were pigment concentration, net photosynthetic rate, (PN), activity of ribulose‐1,5‐bisphosphate carboxylase, (RuBPC), stomatal conductance to CO2, (Gs), and the intercellular partial pressure of CO2, (Ci). Needle growth was rapid, beginning in early May and being complete by the end of the month or early in June. Free growth occurred in the –NR treatment. Photosynthesis increased throughout the season, reaching a peak in August, with some variables subsequently showing a decrease in value. PN increased more rapidly during needle expansion than either chlorophyll concentration or RuBPC activity. Phosphorus deficiency led to a reduction in RuBPC activity, which was restored to the control value following Refertilization with P. Nitrogen deficiency severely reduced values of all variables studied, except Ci, which was higher than for the controls. Refertilization of –N trees caused a very rapid increase in values of all variables, with an increase in Ci, representing a larger increase in mesophyll conductance to CO2, (GM), than GS, PN and RuBPC activity were significantly correlated with total chlorophyll concentration for all treatments, but PN was not correlated with GS or RuBPC activity.
Nitrogen uptake, partitioning and internal cycling inPicea sitchensis(Bong.) Carr. as influenced by nitrogen supply
Authors: MILLARD P. , PROE M. F.
Published: April 2006

Four‐year‐old seedlings ofPicea sitchensis(Bong.) Carr. were grown in sand culture throughout 1989 and irrigated with nutrient solutions containing either 1.0 mol N m−3(Low N) or 6.0 mol N m−3(High N), to precondition their growth and capacity for N storage. During 1990 N enriched with15N was supplied, either from 15 March to 27 June, or 28 June to 20 November. Recovery of unlabelled N was used to determine the storage and immobilization of N for foliage growth, and the partitioning of labelled N taken up during the two periods was measured.

Initial growth of trees in 1990 was unaffected by the current N supply and determined only by the N supplied the previous year. High N throughout increased the number of needles grown in 1990 compared to low N‐treated trees, but had little effect on the dry weight of individual needles. When preconditioned with High N, trees responded to Low N in 1990 by a reduction in needle dry weight, without altering the number of needles produced. Low N trees supplied with High N in 1990 responded by increasing both needle numbers and dry weight, compared with trees supplied with Low N throughout. The amount of unlabelled N remobilized to foliage growth in 1990 was unaffected by the current N supply but reflected the amount of N in store, as determined by the N supply the previous year. The majority of N was remobilized from the 1989 foliage and none from roots. Partitioning of labelled N taken up during 1990 altered during the year, with a greater proportion of N taken up after 28 June recovered in the roots in all treatments, due to root growth as opposed to allocation of N to storage during the autumn, since root N concentrations fell between 17 June and the final harvest on 20 November.
Modification of the Fe protein of the nitrogenase of Gloeothece (Nägeli) sp. ATCC 27152 during growth under alternating light and darkness
Authors: DU CAIGAN , GALLON JOHN R.
Published: April 2006

The Fe protein of the nitrogenase of the unicellular Cyanobacterium Gloeothece (Nägeli) sp. ATCC 27152 can be resolved by SDS–PAGE into two antigenically detectable components of approximate Mr 38500 and 40000 respectively. The larger form of this protein may be produced by modification of the smaller form. Modification of the Fe protein is promoted under conditions where O2 (but not O2− or H2O2) has increased access to the enzyme, but does not allow nitrogenase to function under conditions of O2 stress.

During growth of Gloeothece under alternating light and darkness, antigenically detectable Fe protein is absent throughout most of the light period. The restriction of nitrogenase activity to the period of darkness is better explained in terms of regulation of nitrogenase synthesis and degradation than by reversible modification of a constant intracellular concentration of Fe protein. However, newly synthesized Fe protein always appeared initially as its larger form, which may be catalytically inactive in aerobic cultures of Gloeothece. Conversion of this form to the smaller, assumed active, form of the Fe protein may be an additional factor in explaining the increase in nitrogenase activity that occurs during the first few hours of each dark phase.
The effect of fungicides on vesicular–arbuscular mycorrhizal symbiosis
Authors: SUKARNO N. , SMITH S. E. , SCOTT E. S.
Published: April 2006

This paper describes the effects of the fungicides Benlate, Aliette and Ridomil on plant growth and on mycorrhizal development in onion plants. An attempt was made to distinguish effects on plants from those on the fungus by making comparisons between mycorrhizal plants in the absence of added phosphorus and non‐mycorrhizal equivalent size plants. Vital staining techniques were used to analyse the effects of the fungicides on the living fungus both within the root and in the soil.

Benlate had no effect on shoot dry weight or root length of onion plants whereas a reduction in plant growth was observed following the application of Aliette or Ridomil, in comparison to control plants. Benlate had negative effects on the numbers of living internal hyphae, arbuscules, fungal‐plant interface and living external hyphae in the soil.

Aliette had no effect on the number of living intercellular hyphae and arbuscules. However, it markedly reduced the root length and the length of infected root per plant. These combined effects led to a reduction in the area of the interface between fungus and plant. The length of external hyphae per gram of soil was reduced following the application of Aliette, though not as severely as with Benlate.

Ridomil had more complex effects on vesicular‐arbuscular mycorrhizal symbiosis; treated plants showed a reduction in plant growth and also a reduction in all fungal parameters, namely the number of living intercellular hyphae, arbuscules and fungal–plant interface, the length of infected root and the development of external hyphae in the soil.
CO2 fluxes of cryptogamic crusts
Authors: JEFFRIES D. L. , LINK S. O. , KLOPATEK J. M.
Published: April 2006

The relationship between carbon dioxide exchange of Microcoleus‐ and Scytonema‐dominated cryptogamic crusts and resaturation time was measured in the laboratory with a modified discrete sampling technique and infrared gas analysis. Maximum net photosynthetic rate of Microcoleus was 187 nmol CO2m−2s−1 and of Scytonema was 111 nmol CO2m−2s−1 for rehydration to 100% soil saturation. Both crust types demonstrated a slow rise in resaturation respiration and took 2 days to become fully active after the (first rehydration to 100% soil saturation after long‐term dryness, and only one day to become active after the second rehydration cycle.
A detailed early postglacial (Flandrian) pollen diagram from Cwm Idwal, North Wales
Authors: TIPPING RICHARD
Published: April 2006

Palynological investigation of lacustrine sediments in Llyn Idwal, in the uplands of Snowdonia, North Wales, has shown that pollen assemblages predating those at the base of Godwin's (1955) pollen diagram are recorded. These earlier pollen assemblages do not, however, indicate a revision of the Loch Lomond Readvance age of the last glaciers to occupy the cwm, Arctic‐alpine flora presently growing on the cliffs of Cwm Idwal colonized the catchment as pioneer communities in the earliest postglacial, immediately following ice decay, but appear to have been driven to their present niches very early in the postglacial. Their subsequent reappearance is explained by natural or anthropogenically induced instability in local woodland, or perhaps by increased erosion and stream How affecting pollen transport from cliffs. Evidence is presented of a brief period of arid climate during the expansion of Juniperus, at around 10000 BP.
Altitudinal variation in the response of the vegetation to Late‐glacial climatic events in the northern French Alps
Authors: DAVID FERNAN
Published: April 2006

Pollen and macroscopic plant remains were studied at eight neighbouring sites, in order to define Late‐glacial vegetational history in the northern French Alps. Local pollen assemblage zones are described and indicate that the main elements of vegetational history combine the features of adjacent regions. Herb pollen assemblages are similar to those recorded in the Swiss Late‐glacial, whereas the early occurrence of shrubs and trees is typical of the southern French Alps. An early effect of altitude on vegetation distribution is demonstrated at the end of the Oldest Dryas. At that time the landscape consisted of a patchwork ofArteimisia–Chenopodiaceae steppe, with shrubs in hollows and valleys.Betulawas recorded up lo 700 in andJuniperusup to 1300 m. This altitudinal variation became more pronounced with the arrival of new species. During the Alleröd, mixed stands ofBetulaandPinuswere present up to an altitude of about 1000–1300 m, withBetulareaching 1700 m, this limit depending on factors such as exposure and continentality. The Younger Dryas oscillation is clearly recorded, as at more oceanic N.W. European coastal margins. Nevertheless, the record of the vegetation response to climatic change depends on the elevation of the studied sites. The limit ofPinusstands fell to 700–1000 m. At a lower altitude the climatic signal is weaker and alders [Alnus glutinosa(L.) Gaertn,Alnus incana(L.) Moench] began to spread. Continuous occurrences of alder owing to regional pollen transport are detected up to the highest sites. The empirical limit ofAlnusis therefore proposed as a biostratigraphic marker of the Younger Dryas in the area. Finally. The possibility of a climatic deterioration that started during the late Alleröd is discussed on the basis of absolute chronology.
Cells and tissues in the vegetative sporophytes of early land plants
Authors: EDWARDS DIANNE
Published: April 2006

Remarkable preservation in coalified and pennineralized fossils from Upper Silurian and Lower Devonian sediments deposited some 420 to 390 million years ago provides insight into the major anatomical innovations associated with the early stages in the colonization of the land by higher plants. Using uniformitarian principles, such information, combined with gross morphology, can then be used to reconstruct the pioneers as growing, metabolizing and reproducing organisms, as well as allowing assessment of affinity, although apart from the lycophytes, they have no close relationship with extant groups. In considering vascular tissues, diversity is exemplified by descriptions of the metaxylem in protosteles of Zosterophyllopsida and Drepanophycopsida (putative lycophytes), ofPsilophyton(Trimerophytopsida), of the Rhyniaceae (includingRhynia gwynnevaughanii, certainTaeniocradaspp.,Sennicaulis) and ofCooksonia pertoni, a Lower Devonian representative of the organization found in the oldest pteridophyte‐like land plants.Aglaophyton majoris included as a plant with bryophyte‐like vascular tissues in a branching sporophyte with cuticle, stomata and intercellular space system typical of the homoiohydric tracheophyte. In all water‐conducting cells, interpretation of the primary and secondary wall results from comparisons involving the anatomy and chemistry of extant examples and an understanding of taphonomic processes. Phloem is only rarely preserved and usually identified from its position around the xylem. In contrast, dermal features are better known, because of penetration of the resilient cuticle between epidermal cells. They appear conservative. Thus stomata with two guard cells look remarkably similar to extant forms in surface view, and by consideration of their relationship with surrounding epidermal cells and of extent of cuticularization, seem to have operated in a similar way to those in certain mosses and ferns. Cuticular ornamentation (papillae, striations) and epidermal outgrowths (unicellular and multicellular) are described and their adaptive significance conjectured. Ground tissue systems are best preserved in Rhynie Chert permineralizations where zonation of the cortex is tentatively related to photosynthetic and structural roles. The latter function is also attributed to thick‐walled, outer cortical cells recorded in many zosterophylls and inPsilophyton, although the chemical nature of the walls themselves remains equivocal. Problems of identification of roots in plants possessing axial organization with exarch xylem, and in leafy plants with smooth lateral branching systems are briefly addressed. Finally axis apices inRhynia givynne‐vaughaniiand sections showing stages in the maturation ofAsteroxylonstems are described from the Rhynie Chert.

ContentsSummary225I.Introduction226II.Vascular systems226III.Dermal systems237IV.Ground tissue systems241V.Apical meristems244VI.Distinction of aerial stems, rhizomes and roots245VII.Why anatomy?245Acknowledgements245References245
Plant response to irrigation with water enriched with carbon dioxide
Authors: ENOCH H. Z. , OLESEN J. M.
Published: April 2006

The influence of irrigation with CO2‐enriched water on plant development and yield is reviewed. The reason for irrigation with CO2‐enriched water was – in most cases – to increase yield. The present evaluation considers results from over a hundred studies performed since the first experiment in 1866. Special emphasis is given to the comparison of 85 experiments made by Mitscherlich in 1910 with 358 irrigation experiments made in the last 80 years. In a statistical analysis of these experiments, the measured plant parameter (often growth and/or gas exchange rates) showed a highly significant mean increase of 2.9 % in plants irrigated with CO2‐enriched water as compared with control.

Evidence of five mechanisms was found. The subterranean carbon dioxide concentration influences: (a) the rate of nitrification and hence of nitrogen availability; (b) the rate of weathering and pH, and hence the availability of other plant nutrients; (c) the CO2 uptake via roots into the transpiration stream, contributing to the rate of leaf photosynthesis; (d) the hormone levels in the plant; and (e) the rate of pesticide decomposition in soils.

After examining the available evidence we found that (a) and (b) in some experiments are important to plant growth, since they change the physiochemical environment of the roots. On the other hand, while (c) could theoretically contribute up to 5% of plant carbon assimilation, it usually contributes less than 1 %, while (d) contributes most of the observed effects of CO2‐enriched water on plants. In addition, pesticide decomposition in soils can be delayed by supra‐ or sub‐optimal CO2 concentrations.

Contents

Summary
249

I.
Introduction
249

II.
Historical background
250

III.
Methods for comparing experimental data
251

IV.
Analysis of yield ratios
251

V.
Temporal and spatial changes in the soil atmosphere during and after irrigation with CO2‐enriched water
252

VI.
Mechanisms through which irrigation with CO2‐enriched water influences yield
253

Acknowledgements
256

References
257
Structure and expression of genes coding for structural proteins of the plant cell wall
Authors: JOSÈ MATILDE , PUIGDOMÈNECH PERE
Published: April 2006

The best‐known protein components of the plant cell wall have highly repetitive, proline‐rich sequences. The use of recombinant DNA approaches has enabled complete sequences of these proteins to be determined and features of the expression of the corresponding genes to be examined. These results, coupled with the use of immunological techniques, have shown that proline‐rich proteins are interesting probes to study developmental and defence processes in plants. In this review, the sequence and expression of different groups of proline‐rich proteins in plants are presented. These groups include hydroxyproline‐rich glycoproteins (HRGP) or extensins, proline‐rich proteins (PRP) and glycine‐rich proteins (GRP). The specific features of each group and the possible functions of these proteins are discussed, as well as the data available on the mechanisms controlling the expression of their corresponding genes.

Contents

Summary
259

I.
Introduction
259

II.
Hydroxypioline‐rich glycoproteins (HRGPs)
261

III.
Proline‐rich proteins (PRPs)
270

IV.
Glycine‐rich proteins (GRPs)
274

V.
Concluding remarks
277

References
279
Cloning symbiosis‐related cDNAs from eucalypt ectomycorrhiza by PCR‐assisted differential screening
Authors: TAGU D. , PYTHON M. , CRÉTIN C. , MARTIN F.
Published: April 2006

As part of a project to identify symbiosis‐related genes, we report here a simple differential screening procedure for isolating up‐ and down‐regulated fungal transcripts from a cDNA library of the developing Eucalyptus globulus‐Pisolithus tinctorius mycorrhiza. cDNA inserts of randomly selected λZAP plaques were amplified by PCR and separated by agarose gel electrophoresis. The PCR‐amplified cDNA samples were then screened by Southern blotting, using radiolabelled‐cDNA probes of high specific activity. We have applied this method to fungal transcripts that are differentially expressed in ectomycorrhizas during the early stages of development. We estimate that about 50 % of the fungal mRNA population is regulated by development of the symbiosis; several up‐ and down‐regulated cDNAs have been isolated for further analysis.
Adverse effects of nitrate on stem nodules of Sesbania rostrata Brem*
Authors: KWON DUCK‐KEE , BEEVERS HARRY
Published: April 2006

When the stems of Sesbania rostrata, growing vigorously in nutrient solution, are inoculated with Azorhizobium caulinodans ORS 571 and deprived of nitrate, hundreds of nodules with active N2 fixation (acetylene reduction) develop on each stem within 10 d. The numbers of nodules that develop are not affected by increasing the nitrate concentration in the medium from 0 to 9 mM. However, as the nitrate concentration is raised above about 2 mM the growth of the nodules is strongly inhibited and all aspects of acetylene reduction activity (ARA) are progressively curtailed as the nitrate concentration is increased from zero. In 6 mM nitrate, effects are seen at the earliest possible time of measurement (6 d after inoculation) with maximum inhibition of growth and ARA (about 80%) at 10 d. In plants with stem nodules that have developed in the absence of nitrate since inoculation, the addition of 9 mM nitrate leads to inhibition of further nodule growth and to prompt decrease in specific ARA. The ‘growth’ and ‘activity’ responses of the stem nodules of Sesbania are similar in degree and sensitivity to those of root nodules of other legumes and thus they can no longer be considered as resistant to fixed N.
Uptake and assimilation of nitrite in the acidophilic red alga Cyanidium caldarium Geitler
Authors: FUGGI AMODIO
Published: April 2006

The acidophilic red alga, Cyanidium caldarium Geitler, could use nitrite as a nitrogen source for growth, although this compound was very toxic in acidic media. Growth could be sustained when nitrite was added continuously at a rate lower than the maximum rate of nitrite assimilation for the culture. Nitrite assimilation was derepressed in cells growing on nitrate or nitrite, under nitrogen limitation and by nitrogen starvation. Ammonium‐grown cells showed a limited capacity for nitrite reduction in the light, even if nitrite reductase was not detectable in cell extracts. In acidic media nitrite was taken up mainly through HNO, influx. Nitrite assimilation, in viva, was restricted by a saturable step under conditions in which nitrite uptake was not limiting. The pH of the cell suspension affected nitrite assimilation by changing the K½ over the pH range tested but not the Vmax. The K½ was inversely proportional to the concentration of H+ in the medium. The apparent Km value for nitrite of nitrite reductase, in vitro, and its expected apparent Km value, in vivo, estimated from the K½ of nitrite assimilation, suggested that the activity of this enzyme may not be the limiting step of nitrite assimilation.
Visualizing the distribution of elements within barley leaves by energy dispersive X‐ray image maps (EDX maps)
Authors: WILLIAMS M. L. , THOMAS B. J. , FARRAR J. F. , POLLOCK C. J.
Published: April 2006

X‐ray image maps of transverse sections of barley leaf blades were compared with individual X‐ray emission spectra from vacuoles of barley leaf mesophyll, epidermis and parenchymatous bundle sheath cells. Both forms of X‐ray analysis revealed distinct patterns in element distribution within the leaf blade. Calcium and Cl predominated within the epidermal cell vacuoles whilst P appeared mainly in the mesophyll cell layer. Apparent accumulation of S and Mg within the bundle sheath cell vacuoles is discussed in relation to xylem unloading and sulphur assimilation.
A comparison of sensitivity to ozone in seedlings and trees ofQuercus rubraL.
Authors: SAMUELSON L. J. , EDWARDS G. S.
Published: April 2006

Assessments of ozone sensitivity in tree species have been based primarily on studies of Seedlings without any knowledge of the similarities between seedling and mature tree responses. To determine if seedlings and trees responded similarly to ozone, 2‐yr‐old seedlings and 30‐yr‐old trees ofQuercus rubraL. were fumigated with subambient, ambient and twice‐ambient ozone for one growing season (cumulative doses of 18, 45 and 87 ppm h−1, respectively). Carboxylation efficiency, apparent quantum yield and light‐saturated net photosynthesis of leaves from the lower canopy of the 30‐yr‐old trees were reduced by ambient and twice‐ambient ozone treatment. However, physiological characteristics of leaves from the upper canopy of trees showed no signs of ozone injury. Canopy leaf dry weight of trees was reduced by the twice‐ambient ozone treatment through reductions in leaf area rather than specific leaf weight, but bole diameter and branch growth of trees were unaffected by ozone treatment. In contrast, ozone did not influence leaf physiology of second flush leaves, stem diameter, and height and biomass growth of 2‐yr‐old seedlings. These results indicate that for deciduous hardwood species, studies of seedlings may underestimate the ozone sensitivity of larger and more physiologically mature trees. For large trees with developed canopies, leaf position within the canopy may influence the sensitivity of physiological processes to ozone.
CO2 fluxes of cryptogamic crusts
Authors: JEFFRIES D. L. , LINK S. O. , KLOPATEK J. M.
Published: April 2006

The carbon dioxide exchange of Microcoleus‐ and Scytonema‐dominated cryptogamic crusts as related to dehydration was measured in the laboratory with a modified discrete sampling technique and infrared gas analysis. The dehydration curves predicted that carboxylation and dark respiration rates for both crust types would become zero at from 4 to 5% water content (W) (approximately 16–23% soil saturation), with the water contents at which the rates became zero significantly lower in the second treatment cycle than the first. The dehydration curves predicted that net photosynthesis rates would become zero at 6.7–11.2% W (27–44% soil saturation), with the water contents at which the rates became zero significantly higher in the second cycle of treatment than the first.
Desiccation as the active principle in heat‐stimulated seed germination of Leucospermum R. Br. (Proteaceae) in fynbos*
Authors: BRITS G. J. , CALITZ F. J. , BROWN N. A. C. , MANNING J. C.
Published: April 2006

A new seed biological phenomenon in the myrmecochorous, fire‐recruiting fynbos species Leucospermum cordifolium (Salisb. ex Knight) Fourcade is reported. This is the extensive breaking, following desiccation treatment, of the seed testa which in intact, soil‐stored seeds imposes dormancy on the embryo by means of oxygen exclusion. In this study the pericarps of L. cordifolium seeds were removed and seeds with intact exotestas were selected stereomicroscopically. Samples of seeds were placed in nylon bags and suspended over (cone.) H2SO4 or dried silica gel. A third series of seeds were exposed for varying periods to 40 °C, cooled and immersed in water before performing breakage tests on both the exo‐ and endotesta. All treatments resulted in extensive breaking of the exo‐ as well as the endotesta of seeds. The two ‘cool’ desiccating treatments both caused more effective breaking than heat treatments. This indicates strongly that the breakage phenomena are desiccation effects and not caused directly by heat intensity. Rehydration in air before wetting seeds completely prevented breakage effects in all treatments in the endotesta, but not in the exotesta. This further supports the conclusion that endotesta breakage is a function of desiccation plus wetting and not of heat per se. The results suggest that in nature desiccation by fire could break the exotesta and the endotesta as well, if fire is followed soon by rain. These effects amount to effective scarification of the seed and thus suggest a positive correlation, in nature, between heat intensity of fire and emergent seedling numbers.
Resistance of cowpea [Vigna unguiculata (L.) Walp.] to Striga gesnerioides (Willd.) Vatke, a parasitic angiosperm
Authors: LANE J. A. , BAILEY J. A. , BUTLER R. C. , TERRY P. J.
Published: April 2006

An in vitro growth system was used to investigate the expression of resistance of cowpea [Vigna unguiculata (L.) Walp.] varieties B301 and 58‐57 to the angiosperm parasite Striga gesnerioides (Willd.) Vatke. Variety Blackeye was included in experiments as a susceptible control. Seeds of S. gesnerioides germinated on the roots of all varieties. Two different mechanisms of resistance were expressed in B301 and 58–57 after penetration of host roots by parasite radicles. The first mechanism was expressed in both varieties; host tissue around invading Striga radicles became necrotic in association with the early death of the parasite and lack of tubercle formation. On variety 58–57, the necrosis response was expressed only when the roots were inoculated with Striga from Burkina Faso but Striga from Mali successfully parasitized the roots of variety 58–57. The second mechanism was observed only on variety B301. Striga radicles infected cowpea roots, tubercles were formed but remained at 1–2 mm in diameter with very limited stem growth. No further development of the parasite occurred in vitro or when infected cowpeas were grown in soil or vermiculite. Similarities between the expression of resistance of cowpea to Striga and ot plants to plant pathogenic fungi are discussed.
Plasmodesmata and the supracellular nature of plants
Authors: LUCAS WILLIAM J. , DING BIAO , VAN DER SCHOOT CHRIS
Published: April 2006

In the classical formulation of Münch (1930), plasmodesmata are considered to form simple cytoplasmic bridges between neighbouring plant cells to create the symplasm. This concept has dominated, if not monopolized, the thinking of plant biologists and in particular plant physiologists over the last few decades. Recent advances in ultrastructural, physiological and molecular studies on plasmodesmata indicate that this simple view is in need of revision.

Structurally, the higher plant plasmodesma has been revealed to be a supramolecular complex consisting of membranes and proteins. Functionally, evidence is at hand that this complex structure appears to have evolved not only to control the size exclusion limit for intercellular diffusion of metabolites and small molecules, but also to potentiate and regulate intercellular trafficking of macromolecules, including proteins and nucleic acids. In this regard, plasmodesmal transport may share parallel regulatory mechanisms with nucleocytoplasmic transport.

Based on these findings, we advance the hypothesis that plants function as supracellular, rather than multicellular, organisms. As such, the dynamics of the plant body, including cell differentiation, tissue formation, organogenesis and specialized physiological function(s), is subject to plasmodesmal regulation. Plasmodesmata presumably accomplish such regulatory roles by trafficking informational molecules which orchestrate both metabolic activity and gene expression. Current and future studies on the evolutionary origin(s) of plasmodesmata are likely to provide valuable information in terms of the genetic and molecular basis for the supracellular nature of plants.

ContentsSummary435I.Introduction436II.Plasmodesmal formation, structure and biochemistry436III.Evolution of plasmodesmata445IV.Symplasmic dynamics452V.Plasniodesmal trafficking of macromolecules: parallels with nucleocytoplasmic transport457VI.Role of plasmodesmata in plant development464VII.Concluding remarks469Acknowledgements470References470
Tansley Review No. 59 Leaf boundary layers
Authors: SCHUEPP P. H.
Published: April 2006

Studies of heat and mass exchange between leaves and their local environment are central to our understanding of plant‐atmosphere interactions. The transfer across aerodynamic leaf boundary layers is generally described by non‐dimensional expressions which reflect largely empirical adaptations of engineering models derived for flat plates. This paper reviews studies on leaves, and leaf models with varying degrees of abstraction, in free and forced convection. It discusses implecations of finding for leaf morphology as it affects – and is affected by – the local microclimate. Predictions of transfer from many leaves in plant communities are complicated by physical and physiological feedback mechanisms between leaves and their environment. Some common approaches, and the current challenge of integrating leaf‐atmosphere interactions into models of global relevance, are also briefly addressed.

ContentsSummary477I.Introduction478II.Early studies479III.The formal description of leaf transfer480IV.Effects of turbulence on idealized shapes484V.Effects of aspect ratio and inclination486VI.Leaves and leaf models in forced convection491VII.Leaves and leaf models in mixed and free convection493VIII.Interpretation of leaf shape494IX.Leaves in plant canopies499X.Synopsis and conclusions502References502
Microtubule organization and cell morphogenesis in two semi‐lobed cell types of Adiantum capillus‐veneris L. leaflets
Authors: PANTERIS E. , APOSTOLAKOS P. , GALATIS B.
Published: April 2006

Protodermal cells of Adiantum capillus‐veneris leaflets are polyhedral, displaying regularly arranged cortical microtubules transverse to the main cell axis. The nascent epidermal cells partly detach from the underlying mesophyll cells by formation of intercellular spaces, containing PAS‐positive material.

In early differentiating upper epidermal cells discrete U‐like bundles of cortical microtubules form on the internal periclinal and the anticlinal walls. In contrast, microtubules are randomly scattered along the external periclinal wall. Microtubule bundles of neighbouring anticlinal walls of epidermal cells exhibit an alternating disposition but are directly opposite to those of underlying mesophyll cells. Epidermal cell wall is locally reinforced by thickenings arising under the microtubule bundles and including parallel cellulose microfibrils. The pattern of wall thickenings reflects that of the microtubule bundles. The internal periclinal epidermal cell region expands at the sectors free of wall thickenings, forming several lobes. Simultaneously, intercellular spaces open at the thickened regions of anticlinal walls, which finally become wavy. In contrast, the external periclinal wall does not form any lobes but remains smooth. As a result, epidermal cells become ‘semi‐lobed’. The lobes of lower epidermal cells are less prominent. Mesophyll cells surrounding the endodermis are also ‘semi‐lobed’. Their morphogenesis is achieved by the same mechanism. Colchicine treatment inhibits the ‘semi‐lobed’ morphogenesis of epidermal cells and mesophyll cells surrounding the endodermis and the concomitant intercellular space opening.

These observations reveal that the primary event of ‘semi‐lobed’ cell morphogenesis is the organization of two different patterns of the cortical microtubule cytoskeleton in the same cell.