bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the effect of pulsatile and nonpulsatile shear stress on adherens junctions in human endothelial cells
Authors: Plant S. , Leach L.
Published: March 2003

In vivo, endothelial cells experience shear stress resulting from pulsatile flow. Many publications have shown that the pulsatile nature of this flow influences endothelial function and structure including intracellular calcium concentrations, cell shape and actin stress fibre formation. A recent in vitro study using bovine aortic cells showed exposure to nonpulsatile flow caused transient disruption of adherens junctions through perturbation of VE‐cadherin and the disassembly of the actin cytoskeleton. The aim of this study was to observe the responses of the adherens junctional molecule VE‐cadherin, and F‐actin, to pulsatile and nonpulsatile flow in human endothelial cells over a 48‐h period.

Human umbilical vein endothelial cells (HUVEC) were isolated from fresh umbilical cords taken from elective caesarean sections (n = 6). At passages 2–4 the cells were seeded onto glass coverslips pretreated with 3‐aminoproryaltriethoxysilane (APES). 48 h after reaching confluence the cells were transferred to a parallel plate flow chamber and exposed to slowly increased pulsatile or nonpulsatile laminar flow, producing a final shear stress of 1.5 dynes/cm2. Cells were left under flow for up to 48 h. At t = 0, 8 and 48 h immunocytochemistry was used to visualise VE‐cadherin and phalloidin‐TRITC to visualise F‐actin.

At t = 0, VE‐cadherin was localised at cell‐cell contacts and the cells contained randomly oriented stress fibres and cortically located perijunctional actin. Following 8 h exposure to both types of flow no VE‐cadherin or actin could be detected. After 48 h exposure VE‐cadherin and F‐actin had returned to the junctional regions of the cells exposed to nonpulsatile flow. By comparison in cells exposed to pulsatile flow VE‐cadherin was absent from the cell periphery but was found diffusely throughout the cell. Actin, both stress fibre and cortical, was absent from these cells.

These results show that reassembly of the adherens junction, with a return of VE‐cadherin to cell‐cell contacts and a reformation of the actin cytoskeleton, is only seen in cells that have been exposed to nonpulsatile flow. Further work will show whether such adaptations are merely delayed under pulsatile flow or are prevented from occurring entirely. This study highlights the importance of using pulsatile flow when studying endothelial behaviour.

The financial support of EPSRC and Sulzer Vascutek Ltd is gratefully acknowledged.
Central nervous system phenotypes in craniosynostosis
Authors: Aldridge Kristina , Marsh Jeffrey L. , Govier Daniel , Richtsmeier Joan T.
Published: March 2003

Though reduction in the number of cranial elements through loss of a suture is a recognized trend in vertebrate evolution, the premature closure of cranial sutures in humans, craniosynostosis, is considered a pathological condition. Previous research on craniosynostosis has focused primarily on the skeletal phenotype, but the intimate relationship between the developing central nervous system (CNS) and skull is well documented. We investigate the morphology of the CNS in patients with isolated craniosynostosis through an analysis of cortical and subcortical features using 3‐D magnetic resonance images (MRI). Results show that a distinct CNS phenotype can be defined for specific diagnostic categories. Many differences in CNS morphology observed in the patient samples may be anticipated based on skeletal morphology, but others are not reflected in the skull. We propose a developmental approach to determining the cause of premature suture fusion, which includes investigation of the craniofacial complex as a system, rather than study of isolated tissues.
Cerebellar connections to the rostral reticular nucleus of the thalamus in the rat
Authors: Çavdar Safiye , Onat F. Yilmaz lýz , Yananli Hasan R. , Şehirli Ümit S. , Tulay Cumhur , Saka Erdinç , Gürdal Esra
Published: March 2003

We studied the cerebellar connections to the reticular nucleus thalamus (RNT) by means of retrograde axonal transport of horseradish peroxidase (HRP) in the rat. Specific HRP pressure injections to the rostral RNT (1.6–1.8 mm caudal to bregma) resulted in retrograde labelling of neurones in the cerebellar nuclei. The rostral RNT showed specific topographical organization of its cerebellar connections. Microinjections into the rostral RNT, 1.6 mm caudal to bregma, produced numerous HRP‐labelled neurones within the anterior interposed (emboliform nucleus) and scarce HRP‐labelled neurones within the lateral (dentate nucleus) cerebellar nuclei, whereas injections into the rostral RNT, 1.8 mm caudal to bregma, produced numerous HRP‐labelled neurones within the posterior interposed (globose nucleus) and scarce lightly HRP‐labelled neurones within the lateral (dentate nucleus) cerebellar nuclei. Cerebellar connections with the rostral RNT were exclusively ipsilateral to the injection site. No HRP‐labelled cells were detected in the medial (fastigial nucleus) cerebellar nucleus. The cerebellar connections reach the RNT via the superior cerebellar peduncle. By contrast, HRP injections into the anterior, posterior interposed and lateral cerebellar nuclei produced no labelled cells within the RNT. This study demonstrates the existence of direct cerebello‐RNT but not RNT‐cerebellar connections. The presence of the cerebello‐RNT connections introduces a new route through which the cerebellum may influence RNT and thus cerebral cortical activity.
Purification and characterization of a β‐1,4‐endoxylanase from the ericoid mycorrhizal fungus Hymenoscyphus ericae
Authors: BURKE R. M. , CAIRNEY J. W. G.
Published: March 2003

A β‐l,4‐endoxylanase from the ericoid mycorrhizal fungus H. ericae has been purified to electrophoretic homogeneity using isoelectric focusing, ion exchange and gel permeation chromatography. The enzyme has an isoelectric point of 4.85–5.20 and a molecular weight of 58.4 kDa. The apparent S0.5 of the enzyme for soluble birchwood glucuronoxylan is 3.75 mg ml−1 and the Vmax 468.0 nkatal mg−1 protein. The pH optimum for activity is 4.5 and that for stability is 3.5–4.0; these values are discussed in the context of the pH of the mor humus. The role of wall‐degrading activities in the establishment of the ericoid mycorrhizal symbiosis is considered.
Growth, heterocyst differentiation and nitrogenase activity in the cyanobacteria Anabaena variabilis and Anabaena cylindrica in response to molybdenum and vanadium
Authors: ATTRIDGE E. M. , ROWELL P.
Published: March 2003

summary

This paper reports effects of molybdenum and vanadium on Anabaena variabilis Kutz. (ATCC 29413) and Anabaena cylindrica Lemm. (PCC 7122), previously grown in NH4+‐containing medium deficient in Mo and V (–Mo–V) and then transferred to media lacking combined nitrogen. Diazotrophic growth of A. variabilis was dependent on the presence of Mo or V, with little growth occurring in their absence. Neither Mo nor V was required for heterocyst differentiation in either cyanobacterium, and the highest heterocyst frequencies occurred in cultures showing the lowest growth rates. Although A. cylindrica also showed Mo‐dependent diazotrophic growth and a low rate of growth in the absence of added Mo, the latter was inhibited by addition of 1 μM V. The rate of acetylene reduction by A. variabilis increased rapidly following addition of V to –Mo–V cultures, and increased ethane formation was detected in the acetylene reduction assays. Addition of Mo resulted in a smaller initial increase in the rate of acetylene reduction, but this was also accompanied by increased ethane formation, followed by a slow and much more extensive increase in acetylene reduction with a decrease in ethane formation. These observations indicate that nitrogenase polypeptides, probably those of a V‐nitrogenase, are synthesized in A. variabilis in the absence of added Mo or V, that added Mo can be incorporated into the V‐nitrogenase, and that synthesis of Mo‐nitrogenase is dependent on the presence of Mo. By contrast, A. cylindrica appears either to synthesize only a Mo‐nitrogenase, even in the absence of Mo (though 1 μM V inhibits its synthesis) or to synthesize a Mo‐ and V‐independent nitrogenase, but only in the absence of added Mo and V. Western blots using antisera against the Mo‐Fe and Fe proteins of the Mo‐nitrogenase of Rhodospirillum rubrum indicated the presence of Mo‐nitrogenase polypeptides in both Mo‐grown and –Mo–V grown A. cylindrica, providing evidence in support of the former possibility. Physiologically, the V‐nitrogenase of A. variabilis showed several distinct similarities to the Mo‐nitrogenase of A. cylindrica, including responses to metal concentrations as well as the above responses to addition of V and Mo, respectively.
Fructan biosynthesis in excised leaves of Lolium temulentum VII. Sucrose and fructan hydrolysis by a fructan‐polymerizing enzyme preparation
Authors: CAIRNS ANDREW J. , BONNETT GRAHAM D. , GALLAGHER JOSEPH A. , SIMPSON RICHARD J. , POLLOCK CHRISTOPHER J.
Published: March 2003

A partially purified enzyme preparation from leaves of Lolium temulentum L. was previously shown to catalyse the net synthesis of oligofructans and polyfructans from sucrose. Here the same preparation is shown to catalyse the hydrolysis of both sucrose and oligofructans. The magnitude and properties of these hydrolytic activities have been determined. The significance of these catabolic activities for studies of fructan polymerization both in vitro and in tissues in a physiologically anabolic state are discussed.

The preparation hydrolysed 1‐kestose, 6‐kestose, neokestose, inulin oligosaccharides of low degree of polymerization (DP 4 and 5) and endogenous oligofructans from L. temulentum, with the concomitant release of monosaccharide. The preparation also released reducing sugar at low rates from high molecular weight inulin but had no detectable activity against bacterial levan. Simultaneous incubation of sucrose and Neosugar (a commercially available mixture of predominantly β‐2, 1 linked tri‐, tetra‐ and penta‐saccharides) showed that sucrose was preferentially hydrolysed by the preparation, with Neosugar fructans being protected from hydrolysis at sucrose concentrations >30 mol m−3. The kinetic properties for hydrolysis of both sucrose and Neosugar were determined. For sucrose and Neosugar respectively, Michaelis constants at 30°C and pH 6·0 were 7·7±0·5 and 14·1±1·1 mol m−3 (as terminal fructose) and maximum velocities were 6·5±0·1 and 2·7±0·1 mg g−1 fr. wt h−1 (equivalent to 10·0 and 4·2 nkat g−1 as reducing sugar release). Maximal temperatures for activity were 45 and 44°C, and Arrhenius activation energies were 39·9 and 46·9 kJ mol−1. Preincubations for 1 h at 49 and 48°C caused 50% loss of activity in subsequent assays at 30°C. The pHs for maximal activity for the two substrates were 5·2±0·1 and 5·5±0·1.

Using size exclusion chromatography (SEC), an activity catalysing the formation of fructan oligosaccharides and another catalysing sucrose hydrolysis, were not fully resolved, but exhibited distinct profiles of elution indicating Mr of 57 and 133 kD respectively. When assayed for the hydrolysis of Neosugar, the SEC eluate exhibited two peaks of activity indicative of Mr values of 57 and 133 kD.
The effects of root nitrogen supplies on the absorption of atmospheric NO2 by soybean leaves
Authors: Qiao Z. , MURRAY F.
Published: March 2003

Twelve‐day‐old soybean plants were exposed to atmospheric NO2 (0.3 μM1 1−1) and simultaneously supplied, via the roots, with 5 mM or 1 mM of NaNO3 or NH4C1. After exposure for 7 d, the amount of NO2 absorbed per plant was greater in plants supplied with nitrate than in plants supplied with the same concentration of ammonium. The NO2 AR (absorption rate) decreased with increasing exposure time. At the beginning of exposure, the NO2 AR for all plants was c. 12 mg NO2 h−1 m−2μ1−11. On the day 7 of exposure, the NO2 AR declined to 8.46, 8.97, 8.27, and 9.04 mg NO2 h−1 m−2μ1 1−1 1 for plants receiving 1 mM ammonium, 1 mM nitrate, 5 mM ammonium, and 5 mM nitrate respectively. The plants supplied with nitrate had a higher concentration of leaf nitrate and a higher pH than those supplied with the equivalent concentration of ammonium. These results suggest that the NO2absorption rate might be attenuated by the accumulation of H+ produced from N uptake and assimilation.
The relation of H2S release to SO2, fumigation of lichens
Authors: GRIES CORINNA , ROMAGNI JOANNE G. , NASH THOMAS H. , KUHN UWE , KESSELMEIER JÜRGEN
Published: March 2003

Hydrogen sulphide emission in lichens as a response to low concentration SO2, fumigation was investigated. In an open flow‐through system several lichen species were fumigated with 36 ppb SO2, Two species were also fumigated with higher concentrations (72, 119, 122 and 198 ppb SO2,). Hydrogen sulphide emission was monitored concurrently by cryogenic trapping and analysis with gas chromatography. All tested species increased H, S emission significantly in response to fumigation with 36 ppb SO2. Parmelina tiliacea (L.) Hale and Cladina rangiferina (L.) Wigg. released significantly more H2S (0.098±0.015 and 0.073±0.013 pmol H2S g−1 d. wt s−1, respectively) than Parmelina quercina (Ach.) Hale, Ramalina menziesii Tayl. and Parmelia sulcata Tayl. (0.028 ± 0.01, 0.025±0.014 and 0.023±0.013 pmol H2S g−1 d. wt s−1, respectively). Release of H2S in Hypogymnia physodes was enhanced by increasing SO2 concentrations up to 72 ppb SO2. No significant difference in H2S emission in the dark vs. in the light was found. Generally, no correlation was found between photosynthetic activity and H2S emission for the tested species. Uptake of SO2 was similar for all species, at 24.7 ± 5.6 pmol SO2 g−1 d. wt s−1 in 36 ppb SO2 and increasing at greater SO2 concentrations. Therefore, H2S‐S release represents only 0.11–0.74% of SO2‐S uptake.
Interspecific variation in respiratory and photosynthetic parameters in Antarctic bryophytes
Authors: DAVEY MARTIN C. , ROTHERY PETER
Published: March 2003

summary

Rates of carbon flux in 14 species of Antarctic bryophytes were measured under controlled conditions using an infra‐red gas analysis system. The results were used to produce estimates of mode! parameters for respiration and photosynthesis. The relationships between respiration, photosynthesis, irradiance and temperature followed standard patterns. Temperature optima for gross and net photosynthesis were 10–20 and 0–20 °C respectively, suggesting that the plants were not truly psychrophilic. Photosynthesis was saturated at 30–270 μmol m−2s−1, consistent with the view that bryophytes are, physiologically, shade plants, although there was no evidence of photoinhibition over the range of irradiances tested (up to 700 μmol m−2s−1). Comparison of the results with environmental data suggests that photosynthesis is usually temperature‐limited during daylight in the growing season. Therefore, any change in the temperature of the habitat could affect the productivity of the bryophytes. Rates of photosynthesis varied widely between species, and these relationships were largely maintained over the range of temperatures and irradiances tested. Photosynthetic rankings were correlated with the water availability in the plant habitats, supporting the hypothesis that water is the important factor in determining the distribution of populations in Antarctic habitats.
Locating genotypes and genes for abiotic stress tolerance in barley: a strategy using maps, markers and the wild species
Authors: FORSTER B. P. , RZUSSELL J. R. , ELLIS R. P. , HANDLEY L. L. , ROBINSON D. , HACKETT C. A. , NEVO E. , WAUGH R. , GORDON D. C. , KEITH R. , POWELL W.
Published: March 2003

summary

This paper reviews the results of several years'study by a multidisciplinary team comprising geneticists, physiologists, ecologists and statisticians of abiotic stress tolerance in barley. The strategy involves genetic fingerprinting of wild barley lines (Hordeum spontaneum C. Koch) from a range of habitats and testing these for responses to abiotic stresses under controlled conditions. Multiple regression analysis is used to identify genetic markers associated with experimentally determined stress responses. These data are related to site‐of‐origin ecogeographic data and used to identify areas of useful wild variation. Markers associated with traits of interest can be mapped in genetic mapping populations, revealing areas of the barley genome carrying genes controlling stress responses. This paper highlights our work on associations of amplied fragment length polymorphisms with salt tolerance and describes some initial results of the use of SSRs in studying drought tolerance in barley.
Mapping physiological traits in barley
Authors: ELLIS R. P. , FORSTER B. P. , WAUGH R. , BONAR N. , HANDLEY L. L. , ROBINSON D. , GORDON D. C. , POWELL W.
Published: March 2003

summary

Amplified fragment length polymorphisms (AFLPs) offer a reproducible, multiplex DNA assay by which to genotype mapping populations. We have evaluated physiological traits in barley seedlings grown in an hydroponic system and given a salt treatment. Multiple regression was used to show associations between AFLPs and quantitative traits. Effects at different loci were detected in stress treatments in comparison to the control implying that either novel gene action was induced by salt stress or that normal activity was reduced to a low level where alternate gene action is revealed. The QTLs occurred on all chromosomes but there appeared to be clusters of loci on chromosomes 1 (7H), 4 (4H), 5 (1H) and 6 (6H). The significance of our results is discussed in the context of studies to explore the barley genome and the application of the results of these genetical analyses to barley breeding.
Genetic variability in intergenic spacers of ribosomal DNA in Pisolithus isolates associated with pine, eucalyptus and Afzelia in lowland Kenyan forests
Authors: MARTIN FRANCIS , DELARUELLE CHRISTINE , IVORY MIKE
Published: March 2003

Basidiocarps of Pisolithus associated with indigenous (Afzelia quanzensis Welw.) and introduced (Pinus caribaea Mor. and Eucalyptus camaldulensis Dehnh.) hosts in the lowland forests of the Coast Province of Kenya are morphologically distinct. Genetic variability among 52 Pisolithus basidiocarps, collected beneath the various host plants, was examined based on sequence polymorphism within the internal transcribed spacer (ITS) and intergenic spacer (IGS1) of ribosomal DNA genes. Variability in ITS and IGS1 sequences indicated that the three host‐associated morphotypes were genetically different. Consensus trees generated by bootstrap analysis of sequence data of Pisolithus isolates from Australia and Kenya are polyphyletic and strongly suggest that the three different morphotypes/genotypes present in Kenya represent separate biological species. In addition, our data indicate that little genetic exchange occurs in silva between these species.
Immunocytochemical studies of the infection mechanisms of Botrytis fabae I. The fungal extracellular matrix in penetration and post‐penetration processes
Authors: COLE L. , DEWEY F. M. , HAWES C. R.
Published: March 2003

Extracellular matrices associated with conidia and germ tubes of Botrytis fabae (Sard.) sporelings grown on Vicia faba L. leaves were clearly visualized by epi‐fluorescence microscopy following immunolabelling with the monoclonal antibodies, BC‐KH4 and BC‐FD7‐G9. These antibodies were raised against surface washings of B. cinerea, are directed against B. cinerea and B. fabae, and are known to recognize carbohydrate epitopes on a glycoprotein. Both BC‐KH4 and BC‐FD7‐G9 also labelled matrix material located at the surface of penetration and infection hyphae inside the leaf tissue by epi‐fluorescence microscopy. Such matrix material was not visible by DIC microscopy.

Immunoelectron microscopy of B. fabae‐infected leaf tissue, prepared by progressive low‐temperature dehydration and embedding in acrylic resin, allowed further investigation of the spatial distribution of the antibody‐binding sites. An abundance of BC‐KH4 and BC‐FD7‐G9 antigenic sites were observed throughout the fibrillar‐like matrix material surrounding the germ tubes on the leaf surface and the infection hyphae inside the host cells. However, close examination of the V. faba–B. fabae interface inside the host tissue showed that this fibrillar material extended some distance from the surface of the infection hyphae and through the swollen epidermal and mesophyll cell walls. Such fibrillar matrix material is thought to be of fungal origin. The possible role(s) of this matrix material in the infection process are discussed.

Double‐immunolabelling studies using the BC‐KH4 MAb and a polyclonal antiserum directed against oligosaccharides containing β‐(1→3)‐glucose were carried out in order to localize and distinguish between the fungal extracellular matrix material and translucent cell wall respectively. This technique allowed a closer examination of the interactions of the fungal matrix components with the host walls and degenerate host cytoplasm. Finally, inward curling of the leaf cuticle suggested that mechanical pressure is involved in the penetration process.
The effects of nutrient limitation on the response of Plantago major to ozone
Authors: WHITFIELD C. P. , DAVISON A. W. , ASHENDEN T. W.
Published: March 2003

Most natural and semi‐natural communities are limited by major nutrients such as nitrogen (N) or phosphorus (P), but most experiments on the effects of ozone on wild plants have used nutrient‐rich composts or soil. In order to investigate interactions between ozone and low nutrient supply, two artificially selected lines (ozone‐resistant and ozone‐sensitive) of two populations Plantago major ssp. major L. were grown on a sandy loam, with (HN) and without (LN) addition of fertilizer. The soil was from a semi‐natural grassland that has never been fertilized. Plants were exposed to either charcoal/Purafil®‐filtered air (CF=<5 nl O3 l−1) or 70 nl O3 l−1 7 h d−1 from the seedling stage to seed production.

Poor growth (c. 25% of that in HN) of the low‐nutrient plants, and leaf concentrations of N and P showed that the LN plants were severely nutrient‐limited. In addition to affecting the total dry mass of the plants, the nutrient supply altered seed production, reproductive effort (number of seeds per total mass) and root‐to‐shoot allocation. Exposure to ozone had significant effects on physiology, growth, and seed production that varied with population, selection line, time, and plant development. There also were significant interactions between ozone effects and nutrient regime. In the Lullington Heath population, ozone reduced plant dry weight at 4 wk only in the LN treatment, and in the sensitive line of the Bush population, seed production was reduced by ozone only in LN. Therefore, contrary to what was expected, in the present experiment, plants given the LN treatment were often more sensitive to ozone than those grown under the high‐nutrient regime. This increase in sensitivity was despite the fact that the LN treatment reduced stomatal conductance and ozone flux. It is concluded that there are potentially important interactions between ozone and low nutrient supply that need further investigation, particularly under field conditions.
Persistent, non‐seed‐size maternal effects on life‐history traits in the progeny generation in squash, Cucurbita pepo
Authors: EL‐KEBLAWY ALI , LOVETT‐DOUST JON
Published: March 2003

Maternal‐environmental effects on subsequent progeny life‐history traits were evaluated in squash (Cucurbita pepo L.) in terms of the amount of time available for seed development, and the timing of fruit production. Progeny arising from three kinds of fruit were compared. Plants from which fruits were removed 3 d post‐pollination throughout the growing season developed only ‘late’ fruits (during 10–15 d) at the end of the growing season; on control plants both ‘early’ and ‘late’ fruits developed (both types allowed to ripen fully). Seed from each type of fruit was weighed individually and categorized into three size classes, then germinated and raised to maturity, including regular harvesting of all fruits 3 d post‐pollination. Maternal effects were evident for both vegetative and reproductive traits and carried over to later stages. In contrast, effects due simply to seed size disappeared by day 30 for leaf variables and day 60 for male flower production. Within a seed‐size class, progeny arising from fruit of treated plants produced significantly more leaves, with greater size, and more male flowers than those arising from fruit of control plants, while the reverse was true for fruit number and fruit mass. This result is discussed in terms of possible gibberellic acid involvement. In control plants, progeny arising from seeds in the large, fully mature ‘early’ fruits produced significantly more, and larger leaves by day 30 than did those from late fruits (suggesting differential provisioning in seeds during development). Male flower production had a highly significant positive correlation with vegetative mass and a significant negative correlation with fruit production.
Regulation of arbuscular mycorrhizal development by plant host and fungus species in alfalfa
Authors: DOUDS, Jr. D. D. , GALVEZ L. , BÉCARD G. , KAPULNIK Y.
Published: March 2003

Two cvs of alfalfa (Medicago sativa L.), Gilboa and Moapa 69, were inoculated in glasshouse pots with three arbuscular mycorrhizal (AM) fungi to investigate the efficacy of mycorrhizas with respect to the extent of colonization and sporulation. Paspalum notatum Flugge also was inoculated to describe fungal parameters on a routine pot culture host. Percentage root length of P. notatum colonized by Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe, Glomus intraradices Schenck & Smith, and Gigaspora margarita Becker & Hall increased from 10 to 21 wk, and all fungi sporulated during that period. In alfalfa, only colonization by G. intraradices increased over that time period, and it was the only fungus to sporulate in association with alfalfa at 10 wk. Glomus mosseae did not sporulate after 16–21 wk despite having colonized 30–35% of the root length of both alfalfa cvs. In vitro experiments in which Ri T‐DNA‐transformed roots of alfalfa were inoculated with AM fungi showed normal mycorrhizal formation by G. intraradices and a hypersensitivity‐like response to Gi. margarita. Colonized cells became necrotic, and HPLC analysis indicated increased concentrations of phenolics and isoflavonoids in these root segments. These data strongly support the existence of a degree of specificity between AM fungi and host that might rely on specific biochemical regulatory processes initiated in the host as a result of the attempts at colonization by the fungus.
Biological clocks in Arabidopsis thaliana
Authors: MILLAR ANDREW J.
Published: March 2003

Biological rhythms are ubiquitous in eukaryotes, and the best understood of these occur with a period of approximately a day – circadian rhythms. Such rhythms persist even when the organism is placed under constant conditions, with a period that is close, but not exactly equal, to 24 h, and are driven by an endogenous timer – one of the many ‘biological clocks’. In plants, research into circadian rhythms has been driven forward by genetic experiments using Arabidopsis. Higher plant genomes include a particularly large number of genes involved in metabolism, and circadian rhythms may well provide the necessary coordination for the control of these – for example, around the diurnal rhythm of photosynthesis – to suit changing developmental or environmental conditions. The endogenous timer must be flexible enough to support these requirements. Current research supports this notion most strongly for the input pathway, in which multiple photoreceptors have been shown to mediate light input to the clock. Both input and output components are now related to putative circadian oscillator mechanisms by sequence homology or by experimental observation. It appears that the pathways linking some domains of the basic clock model may be very short indeed, or the mechanisms of these domains may overlap. Components of the first plant circadian output pathway to be identified unequivocally will help to determine exactly how many output pathways control the various phases of overt rhythms in plants.

contents

Summary
175

I.
the circadian system
176

II.
overt circadian rhythms
177

III.
photoperiodism
183

IV.
oscillator theory and practice
186

V.
phototransduction pathways
190

VI.
conclusions
192

Acknowledgements
193

References
193
Process of tomato root colonization by a pathogenic strain of Fusarium oxysporum f. sp. lycopersici in comparison with a non‐pathogenic strain
Authors: OLIVAIN CHANTAL , ALABOUVETTE CLAUDE
Published: March 2003

A pathogenic strain of Fusarium oxysporum f. sp. lycopersici transformed with the glucuronidase (GUS) reporter gene was used to study the colonization process of tomato (Lycopersicon esculentum) roots in hydroponic culture. The plants were treated exactly as those used in a different study with a non‐pathogenic strain of F. oxysporum in order to compare the two types of colonization process. The pathogenic strain rapidly colonized the root surface, forming a dense network of hyphae – shown by the GUS staining assay – as early as 48 h after inoculation. The first images of the pathogen penetrating into the epidermis of the root were observed 24 h after inoculation. The plant showed defence reactions mainly in the hypodermis, but also in the cortex. Generally these barriers failed to prevent the centripetal growth of the pathogen towards the stele. The GUS activity moved with the actively growing hyphae into the tissues; the stele appeared intensely stained 7 d after inoculation, whereas by this time the hyphae at the root surface did not show any more staining. The hyphae formed a dense network at the apex of the root, but direct contact between hyphae and living cells was prevented by several layers of sloughed cap cells. Although rarely observed, penetration of the pathogen into the apex was possible and led to a rapid destruction of apical cells. The only differences between this pattern of root colonization and that observed for a non‐pathogenic strain of F. oxysporum appear to concern the frequency of dead apices and the intensity of fungal colonization in the cortex. When the pathogen passed around the barrier formed in the hypodermis it always reached the xylem, although this barrier and other defence reactions induced at different levels in the cortex always prevented the non‐pathogenic strain from reaching the stele. These observations suggest that the main differences between the two types of interaction – between the plant and either the pathogenic or the non‐pathogenic strain – are quantitative rather than qualitative.
Cross‐colonization of Scots pine (Pinus sylvestris) seedlings by the ectomycorrhizal fungus Paxillus involutus in the presence of inhibitory levels of Cd and Zn
Authors: HARTLEY JEANETTE , CAIRNEY JOHN W. G. , MEHARG ANDREW A.
Published: March 2003

The effects of Cd and Zn on cross‐colonization by Paxillus involutus of Scots pine seedlings was examined by using pairs of ectomycorrhizal (ECM) and non‐mycorrhizal (NM) seedlings grown in the same vessel. This was done to assess, first, the ability of P. involutus to colonize NM Scots pine seedlings by growth from colonized roots of other Scots pine seedlings in the presence of Cd or Zn, and, second whether ECM colonization of Scots pine by P. involutus provided a competitive advantage over NM seedlings. Ectomycorrhizal colonization of Scots pine was shown to be more sensitive than Scots pine itself to Cd and Zn, but prior colonization did provide a competitive advantage with respect to biomass production. This beneficial effect over NM seedlings was, however, equal in the control, Cd and Zn treatments, and was due simply to growth stimulation in the presence of ECM colonization. Cross‐colonization from an ECM to a NM seedling was reduced but not prevented by Cd and Zn. Cd had a more negative effect on cross‐colonization than on initial colonization of seedlings, whereas Zn had an equally inhibitory effect on both parameters. These results have important implications for plant establishment on metal‐contaminated sites. If cross‐colonization between plants is reduced by toxic metals, plant establishment on contaminated sites might be retarded.
Endoproteolytic activities in pea roots inoculated with the arbuscular mycorrhizal fungus Glomus mosseae and/or Aphanomyces euteiches in relation to bioprotection
Authors: SLEZACK S. , DUMAS‐GAUDOT E. , ROSENDAHL S. , KJØLLER R. , PAYNOT M. , NEGREL J. , GIANINAZZI S.
Published: March 2003

Arbuscular mycorrhizal (AM) symbioses are known to play a role in increased resistance of plants against soilborne pathogens. Mechanisms involved in this phenomenon are not yet well understood. This work investigates possible roles of endoproteolytic activities in bioprotection of Pisum sativum roots by Glomus mosseae against Aphanomyces euteiches. First, it is demonstrated that bioprotection occurs only in pre‐mycorrhizal plants. Second, endoproteolytic activities were analysed qualitatively and quantitatively during AM symbiosis, in plants infected with either zoospores or mycelium of A. euteiches, and in mycorrhizal plants infected with the pathogen. In mycorrhizal symbiosis a progressive increase in endoproteolytic activities was observed following root colonization by G. mosseae. By contrast, in roots inoculated with A. euteiches, a drastic increase in endoproteolytic activities was observed which was correlated with the amount of pathogen occurring in roots. Qualitative differences were seen among the endoproteolytic activities detected in roots inoculated with zoospores or mycelium. The constitutive as well as mycorrhizal and pathogen‐induced activities were further characterized as ‘trypsin‐like’ serine endoproteases. Interestingly, in a situation of bioprotection, only low levels of the activities normally associated with the infection by A. euteiches were detected, suggesting that the synthesis of these proteins is directly linked to the growth or virulence of the pathogen.
Response of subterranean clover (Trifolium subterraneum) to ozone in relation to plant age and light conditions during exposure
Authors: SILD EBE , PLEIJEL HÅKAN , SELLDÉN GUN
Published: March 2003

Potted subterranean clover (Trifolium subterraneum) plants of different ages were exposed to 70 nl l−1 ozone for 6 h, either during the light or during the dark period in a laboratory‐based climate chamber. There was limited visible leaf injury on plants which were 14–20 and 28–34 d old and no significant decrease in biomass after daytime ozone exposure. The oldest leaves of 22–26 d old plants exhibited severe visible injury, which was associated with a significant reduction in biomass in 24–26 d old plants. Thus, ozone‐induced visible injury of different magnitude developed in all plants, but was associated with biomass reduction only during a limited period of the plant's life‐span. Apart from modifying ozone uptake by plants, climatic conditions are important as growth modifiers. It is suggested that subterranean clover plants of defined developmental stages should be used in bioindication of ozone. Night ozone exposure injured significantly fewer leaves than day exposure. However, some leaves developed visible injury even after night ozone exposure. Night uptake of ozone may be of more importance in northern than in central and southern Europe, because summer nights are short and, for a certain period, never completely dark.
Juncus bulbosus as a pioneer species in acidic lignite mining lakes: interactions, mechanism and survival strategies
Authors: CHABBI ABAD
Published: March 2003

Bulbous rush (Juncus bulbosus) initiates plant colonization in extremely acid lakes resulting from coal mining operations. Various analytical techniques (methylene blue/agar method, Ti3+‐citrate solution) X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Energy‐dispersive X‐ray (EDX) were used to assess the mechanisms and strategies employed by J. bulbosus to overcome the extreme conditions. The plant releases oxygen into the rhizosphere in turn increasing the redox potential and inducing iron oxide plaque formation. XRD showed that the iron oxide of the plaque is mainly goethite that has been developed in the presence of CO2; SEM showed that there is a micro‐space between the roots and sand grains which is inhabited by microorganisms. Furthermore, SEM‐EDX studies on internal iron distribution demonstrate that iron toxicity is delayed by the physiological and biochemical structure of the plant. It is suggested that J. bulbosus uses a variety of mechanisms and strategies (morphological, physiological and biochemical adaptation) which are mainly complementary and which interact with each other to help J. bulbosus to manage its growth and survival in an extreme environment.
Mechanistic basis of differences in water‐use efficiency between a CAM and a C3 species of Peperomia (Piperaceae)
Authors: WOERNER AUDREY C. , MARTIN CRAIG E.
Published: March 2003

Under ecologically realistic environmental conditions, the water‐use efficiency (WUE) of Peperomia scandens, a CAM plant, was higher than that of the C3 congener P. obtusifolia. This difference has been attributed to differences in stomatal activity between C3 and CAM plants, coupled with differences in the evaporative demand of the atmosphere during which the stomata are open. This explanation has apparently not, however, been experimentally tested. Thus, WUEs were compared in these species in two experiments in which the atmospheric evaporative demand was identical (or nearly so) during the period of stomatal opening (i.e. during the night for the CAM plant and during the day for the C3 species). In both experiments, the WUE of the CAM species was higher than that of the C3 species. These results suggest that factors other than differences in atmospheric environmental conditions must also be responsible for the observed differences in WUE. Because CO2 uptake rates of the CAM species were substantially lower than those of the C3 species, the lower WUE in the CAM species resulted primarily from lower transpiration rates. Lower rates of water loss in P. scandens, relative to rates in P. obtusifolia, were ascribed, in part, to lower stomatal densities. Thus, leaf morphological differences, in addition to differences in atmospheric evaporative demand, help to explain the high WUE typically measured in CAM plants.
Evaluation of the population dynamics of the forage legume (Lotus corniculatus), using matrix population models
Authors: EMERY K. M. , BEUSELINCK P. , ENGLISH J. T.
Published: March 2003

The population dynamics of perennial crop plants are influenced by numerous factors, including management practices. Conditions in the field vary from year to year, and matrix population models are useful for evaluating population behaviour in relation to environmental variability. In Missouri, the stand persistence of birdsfoot trefoil (Lotus corniculatus), a perennial legume, is often limited by disease and poor seed production. A stage‐based, matrix population model was developed to evaluate the population dynamics of birdsfoot trefoil in relation to clipping treatment. The plant growth stages represented in the model were seeds, seedlings, mature vegetative and reproductive plants. Two phases of population growth were evaluated in clipped and unclipped stands. Establishment‐phase populations were characterized by relatively high mortality and low reproduction. Elasticity analysis indicated that growth of these populations was most sensitive to the survival of vegetative plants. Mature vegetative plants and seeds comprised the majority of surviving individuals in clipped and unclipped populations, respectively; however, establishment‐phase populations under both management treatments tended toward extinction. Populations in the post‐establishment phase of growth were characterized by relatively low mortality and high reproduction. Population growth in this phase of growth was most sensitive to seed production, and most individuals in these populations were at the seed stage.
Vegetative reproduction by species with different adaptations to shallow‐flooded habitats
Authors: LENSSEN J. P. M. , MENTING F. B. J. , VAN DER PUTTEN W. H. , BLOM C. W. P. M.
Published: March 2003

In shallow flooded parts of rich fens Mentha aquatica might thrive in deeper water than Epilobium hirsutum but previous experiments have provided no clear indication that the flooding tolerance of these species differs. In this study we investigated, by measuring growth, biomass allocation and vegetative reproduction, whether the impact of water level on vegetative reproduction might produce different lower boundaries on water level gradients. There was a striking contrast between biomass production at high water levels and the field distribution of both species. After 18 wk, the mean biomass of E. hirsutum grown in waterlogged and flooded conditions was 82% and 54%, respectively, of the mean biomass production of drained plants. Biomass of waterlogged and flooded M. aquatica was reduced to 57% and 37% in drained conditions. Waterlogged and flooded E. hirsutum had swollen stem bases and invested a high proportion of biomass in adventitious roots. Stems of M. aquatica did not swell, formed few adventitious roots and maintained an equal proportion of below‐ground roots at all water levels. The effect of water level on vegetative reproduction corresponded well with the lower hydrological boundaries of both species. When waterlogged and flooded, most rhizomes of E. hirsutum emerged from above‐ground parts of the stem base and were oriented in an upward direction. Plants in flooded soil allocated less biomass to rhizomes and also reduced the number and size of rhizomes. Rhizome formation of M. aquatica on the other hand was not directly affected by water level and only depended on plant size. These differences in vegetative reproduction are discussed in relation to the different abilities of both species to oxygenate their below‐ground roots. It was concluded that the mode of adaptation to soil flooding might also affect vegetative reproduction and, therefore, a species' ability for long‐term persistence in soil‐flooded habitats.
Mobilization and transfer of nutrients from litter to tree seedlings via the vegetative mycelium of ectomycorrhizal plants
Authors: PEREZ‐MORENO J. , READ D. J.
Published: March 2003

The ability of the mycorrhizal fungus Paxillus involutus to mobilize nitrogen and phosphorus from discrete patches of beech (Fagus sylvatica), birch (Betula pendula) and pine (Pinus sylvestris) litter collected from the fermentation horizon of three forest soils, and to transfer the nutrients to colonized B. pendula Roth seedlings, was investigated in transparent observation chambers. The mycelium of P. involutus foraged intensively in all three types of litter, leading to a significant decline in their phosphorus contents after 90 d. Over the same period only one of the litter types, beech, showed more than a 10% loss of its N contents. Exploitation of the litter led to invigoration of the vegetative mycelium of the fungus throughout the chambers as well as to significant increases of biomass production and leaf area in seedlings grown in the plus litter (+L) relative to those in minus litter (−L) systems. The yield increases were associated with gains in whole plant tissue content and concentration of P, but in content only in the case of N. Calculations suggest that a major proportion of the phosphorus lost from litter originated in its organic fraction. The possible basis of the discrepancy between values of N loss from litter and gain by the plant is discussed and the extent to which the distinctive pattern of nutrient mobilization is a feature peculiar to this fungus‐plant combination is considered. It is concluded that nutrient mobilization from natural organic substrates in the fermentation horizon of forest soils may be a key function of the vegetative mycelium of mycorrhizal systems. The need for experimental analyses of a greater range of fungus‐plant partnerships is stressed.
Hydraulic architecture of Monstera acuminata: evolutionary consequences of the hemiepiphytic growth form
Authors: LÓPEZ‐PORTILLO J. , EWERS F. W. , ANGELES G. , FISHER J. B.
Published: March 2003

The hydraulic architecture of the secondary hemiepiphyte Monstera acuminata was examined in native plants from Los Tuxtlas, Veracruz, Mexico, to determine how it compared to better‐known growth forms such as trees, shrubs, lianas and primary hemiepiphytes. Monstera acuminata starts its life cycle as a prostrate herb. As it ascends a tree or other vertical support, the stem becomes thicker, produces larger leaves, and may die back from the base upwards until only aerial feeding roots serve to connect the stem to the soil. Unlike the pattern of vessel‐size distribution along the stems of woody dicotyledons, M. acuminata has its wider vessels at the top of the stem, decreasing in diameter towards the base. Also peculiar is the fact that Huber values (axis area/distal leaf area) tend to increase exponentially at higher positions within the plant. Based on the hydraulic conductivity (kh) and leaf‐specific conductivity (LSC, kh/distal leaf area), the base of the stem potentially acts as a severe hydraulic constriction. This constriction is apparently not limiting, as aerial roots are produced further up the stem. The plants have remarkably strong root pressures, up to 225 kPa, which may contribute to the maintenance of functional vessels by refilling them at night or during periods of very high atmospheric humidity, as in foggy weather and rain. In common with dicotyledonous plants, vessel length, vessel diameter, kh, specific conductivity (ks, kh/axis area) and LSCs were all positively correlated with axis diameter. The features of the hydraulic architecture of M. acuminata may be an evolutionary consequence of an anatomical constraint (lack of vascular cambium and therefore of secondary growth) and the special requirements of the hemiepiphytic growth form.
Monstrous plant architecture
Authors: Rowe Nick
Published: March 2003

Monstera acuminata is a plant with a problem – it attains a large body size, yet has no secondary growth. For many years, observers have noted the differences in architecture between monocots and woody dicots, particularly in terms of overall size and comparisons of tree‐like forms. However, very little is known about the functional morphology of smaller‐bodied and ecologically significant climbing and hemiepiphytic monocots, of which M. acuminata is one. In its wider context, the diversity of plant growth forms contributes to the complex structure of many terrestrial ecosystems, where herbs, trees, shrubs, vines, lianas, root‐climbers, epiphytes and hemiepiphytes may be said to comprise the ‘skeleton’ of the ecosystem (Speck & Rowe, 1999). This is seen readily, for example, in the humid tropics, which arguably possess the highest taxonomic and structural diversity that has ever been formed by plants on earth. In this issue, López‐Portillo et al. (pp. 289–299) investigate the development of plant architecture in Monstera, and demonstrate a range of novel hydraulic parameters.