bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of reaction zone penetration by decay fungi in wood of beech (Fagus sylvatica)
Authors: SCHWARZE F. W. M. R. , BAUM S.
Published: March 2003

Fungal growth within reaction zones of beech (Fagus sylvatica) challenged by three basidiomycetes, Inonotus hispidus, Ganoderma adspersum, Fomitopsis pinicola, and one ascomycete, Ustulina deusta, was studied in naturally colonized and artificially inoculated wood. All the fungi, except F. pinicola, breached reaction zones, but the mechanisms involved were all somewhat different. Both I. hispidus and U. deusta bypassed blocked cell lumina by tunnelling through cell walls (soft‐rot mode), but the latter caused far more decomposition of cell walls. Degradation of polyphenols was slight with I. hispidus and absent with U. deusta. By contrast, G. adspersum preferentially degraded the polyphenolic occlusions in the cell lumina. The failure of F. pinicola to invade reaction zones was typical of a brown rot fungus having limited enzymatic potential and a uniform growth pattern. Mechanisms of lesion expansion, illustrated and summarized in schematic diagrams, are consistent with earlier observations that reaction zones in beech sapwood are static boundaries, which may be successfully breached by white and soft‐rot fungi.
Tansley Review No. 112
Authors: FOYER CHRISTINE H. , NOCTOR GRAHAM
Published: March 2003

The gradual but huge increase in atmospheric O2 concentration that followed the evolution of oxygenic
photosynthesis is one consequence that marks this event as one of the most significant in the earth's history. The
high redox potential of the O2/water couple makes it an extremely powerful electron sink that enables energy to
be transduced in respiration. In addition to the tetravalent interconversion of O2 and water, there exist a plethora
of reactions that involve the partial reduction of O2 or photodynamic energy transfer to produce active oxygen
species (AOS). All these redox reactions have become integrated during evolution into the aerobic photosynthetic
cell. This review considers photosynthesis as a whole‐cell process, in which O2 and AOS are involved in reactions
at both photosystems, enzyme regulation in the chloroplast stroma, photorespiration, and mitochondrial electron
transport in the light. In addition, oxidants and antioxidants are discussed as metabolic indicators of redox status,
acting as sensors and signal molecules leading to acclimatory responses. Our aim throughout is to assess the
insights gained from the application of mutagenesis and transformation techniques to studies of the role of O2 and related redox components in the integrated regulation of photosynthesis.

contents

I.
Introduction
360

II.
Photoinhibition and active oxygen
360

III.
Oxygen as an electron acceptor
362

IV.
Redox regulation of photosynthetic metabolism
368

V.
Photorespiration
369

VI.
Respiration
376

VII.
Photosynthesis and redox signal transduction
378

VIII.
Conclusions
380

Acknowledgements
381

References
381
Ecto‐ or arbuscular mycorrhizas – which are best?
Authors: Lodge D. J.
Published: March 2003

Few topics in ecology are as intriguing or bedeviling as comparative studies of different types of mycorrhizas formed in the same plant species. Attempts to determine the relative benefits from each fungal type to the host plant are fraught with difficulties (Jones et al., 1998), and for this
reason plants that form tripartite associations with arbuscular
and ectomycorrhizal fungi make ideal experimental
systems. Just such a tripartite system is explored in a
report in this issue by Chen et al. (pp. 545–556).

Why compare mycorrhizas? Although both ecto‐ and arbuscular mycorrhizas are generally known to increase the uptake of nutrients such as phosphorus and nitrogen in infertile soils, their functions and the benefits they provide to their host plants may not be equivalent (Jones et al., 1998). Hence the ecological benefits of the two types of symbiosis are of great interest to plant community ecologists and researchers studying nutrient cycling. Arbuscular mycorrhizas are formed as a symbiosis of plant roots with primitive fungi of the order Glomales (Zygomycetes), while ectomycorrhizas are formed with higher basidiomycetes and a few ascomycetes. Only a few plant genera and species are capable of forming both types of association, sometimes on the same root tip (Fig. 1), but it is these that are so useful in comparative studies.
Response of root respiration to changes in temperature and its relevance to global warming
Authors: ATKIN OWEN K. , EDWARDS EVERARD J. , LOVEYS BETH R.
Published: March 2003

Global warming over the next century is likely to be associated with a change in the extent to which atmospheric and soil temperatures fluctuate, on both a daily and a seasonal basis. The average annual temperature of the Earth's surface is expected to increase, as is the frequency of hot days. In this review, we explore what effects short‐term and long‐term changes in temperature are likely to have on root respiratory metabolism, and what impacts such changes will have on daily, seasonal and annual CO2 release by roots under field conditions. We demonstrate that
Q10 values, and the degree of acclimation, differ between and within plant species. Changes in the temperature
sensitivity of respiration with measuring temperature are highlighted. Temperature‐dependent changes in
adenylate control and substrate supply are likely to control the Q10 and degree of acclimation of root respiration.
Limitations in respiration capacity are unlikely to control respiratory flux at most temperatures. The potential role
of nonphosphorylating pathways such as the alternative oxidase in controlling Q10 values is highlighted. The
possibility that potentially rapid changes in adenylate control might underlie the acclimation response (rather than
slow changes in enzyme capacity) has implications for the total amount of CO2 respired by roots daily and
annually. Our modelling suggests that rapid acclimation will result in near‐perfect homeostasis of respiration rates
and minimize annual CO2 release. However, annual CO2 release increases substantially if the speed of full
acclimation is lower. Our modelling exercise also shows that high Q10 values have the potential to increase daily
and annual CO2 release substantially, particularly if the frequency of hot days increases after global warming.
Responses of tree fine roots to temperature
Authors: PREGITZER KURT S. , KING JOHN S. , BURTON ANDREW J. , BROWN SHANNON E.
Published: March 2003

Soil temperature can influence the functioning of roots in many ways. If soil moisture and nutrient availability are adequate, rates of root length extension and root mortality increase with increasing soil temperature, at least up to an optimal temperature for root growth, which seems to vary among taxa. Root growth and root mortality are highly seasonal in perennial plants, with a flush of growth in spring and significant mortality in the fall. At present we do not understand whether root growth phenology responds to the same temperature cues that are known to control shoot growth. We also do not understand whether the flush of root growth in the spring depends on the utilization of stored nonstructural carbohydrates, or if it is fueled by current photosynthate. Root respiration increases exponentially with temperature, but Q10 values range widely from c. 1.5 to > 3.0. Significant questions yet to be resolved are: whether rates of root respiration acclimate to soil temperature, and what mechanisms control acclimation if it occurs. Limited data suggest that fine roots depend heavily on the import of new carbon (C) from the canopy during the growing season. We hypothesize that root growth and root respiration are tightly linked to whole‐canopy assimilation through complex source–sink relationships within the plant. Our understanding of how the whole plant responds to dynamic changes in soil temperature, moisture and nutrient availability is poor, even though it is well known that multiple growth‐limiting resources change simultaneously through time during a typical growing season. We review the interactions between soil temperature and other growth‐limiting factors to illustrate how simple generalizations about temperature and root functioning can be misleading.
Persistence of the gelatinous layer within altered tension‐wood fibres of beech degraded by Ustulina deusta
Authors: BAUM S. , SCHWARZE F. W. M. R. , FINK S.
Published: March 2003

The gelatinous layer (G‐layer) of tension‐wood fibres in reaction wood of beech showed alterations as a result of the physiological processes involved in the conversion of sapwood into false heartwood or reaction‐zone tissue. Using transmitted‐light, fluorescence and UV microscopy, polyphenolic compounds were found to infiltrate and encrust the cellulose microfibrils within the G‐layer. Experiments with naturally infected and artificially inoculated wood showed that these processes affect the rate and mode of degradation by wood‐decaying fungi. Thus, although the ascomycete Ustulina deusta was able to degrade the G‐layer from within the lumina of tension‐wood fibres in unaltered sapwood, it failed to do so for a prolonged period within false heartwood and reaction zones. In both situations, however, there was some degradation of the underlying secondary wall in the form of erosion troughs which can be attributed to soft rot ‘type II’, and internal cavity formation typical for ‘type I’ attack. The present study indicates that not only cell type, but also alterations in the cell wall structure, affect the activity and degradation mode of decay fungi in beech.
Tree and forest functioning in response to global warming
Authors: Saxe Henrik , Cannell Melvin G. R. , Johnsen Øystein , Ryan Michael G. , Vourlitis George
Published: March 2003

Although trees have responded to global warming in the past – to temperatures higher than they are now – the rate of change predicted in the 21st century is likely to be unprecedented. Greenhouse gas emissions could cause a 3–6°C increase in mean land surface temperature at high and temperate latitudes. Despite this, few experiments have isolated the effects of temperature for this scenario on trees and forests. This review focuses on tree and forest responses at boreal and temperate latitudes, ranging from the cellular to the ecosystem level. Adaptation to varying temperatures revolves around the trade‐off between utilizing the full growing season and minimizing frost damage through proper timing of hardening in autumn and dehardening in spring. But the evolutionary change in these traits must be sufficiently rapid to compensate for the temperature changes. Many species have a positive response to increased temperature – but how close are we to the optima? Management is critical for a positive response of forest growth to a warmer climate, and selection of the best species for the new conditions will be of vital importance.ContentsSummary369I.Introduction370II.Photosynthesis and respiration370III.Soil organic matter decomposition and mineralization373IV.Phenology and frost hardiness376V.Whole tree experimental responses to warming380VI.Changes in species distribution at warmer temperatures381VII.Adaptation and evolution383VIII.Ecosystem level responses to warming387Acknowledgements390References390Appendix I.Temperature response functions399
Structure of fructans in roots and leaf tissues of Lolium perenne
Authors: Pavis N. , Chatterton N. J. , Harrison P. A. , Baumgartner S. , Praznik W. , Boucaud J. , Prud’homme M. P.
Published: March 2003

An analysis of fructan structures, to increase the understanding of biosynthetic pathways and enzymology of fructan synthesis in root and leaf tissues of Lolium perenne is reported.

Fructan extracted from stubble of L. perenne plants was analyzed by high performance anion exchange chromatography and pulsed amperometric detection (HPAEC‐PAD) using a new desalting technique. Structures of fructan isomers, separated up to DP16 (DP, degree of polymerization), were established by chromatographic elution times or by GC‐MS.

Fructans of DP8 belonged essentially to three series: inulin series, inulin neoseries and the levan neoseries, which is/are different in glucose (terminal or internal) and linked fructose residues. High DP fructans (DP > 8) comprised 75% molecules with an internal glucose residue. They had some branch points although 1 and 6 kestotetraose could not be detected and the β(2–6) linked fructose residues were 70 times more abundant than the β(2–1) linked fructose residues. Roots, sheaths, leaf blades and elongating leaves accumulated similar fructans although amounts of both low and high, and types of low, DP fructans, differed.

It is proposed that fructans in L. perenne are synthesized via four enzymes: 1‐SST (1‐sucrose‐sucrosefructosyl transferase), 1‐FFT (1‐fructan‐fructanfructosyl transferase), 6G‐FT (6‐glucose‐fructosyl transferase) and 6‐FFT (6‐fructan‐fructanfructosyl transferase) or 6‐SFT (6‐sucrose‐fructanfructosyl transferase).
Physiological responses of Catharanthus roseus (periwinkle) to ash yellows phytoplasmal infection
Authors: Tan Puay Yok , Whitlow Thomas
Published: March 2003

Photosynthetic responses of periwinkle (Catharanthus roseus) were compared during disease development after infection by two strains of ash yellows (AshY) phytoplasmas that differed in aggressiveness.

 Healthy plants were inoculated by grafting with diseased scions. Mature leaves formed before grafting of diseased scion, and leaves formed during disease development were monitored for physiological changes.

 Leaves formed before inoculation remained visually and physiologically asymptomatic until normal senescence. However, leaves formed after inoculation had reduced photosynthesis, due to reductions in both the maximum carboxylation rate (Vcmax) and noncyclic electron transport (Jmax). In these leaves, photoinhibition resulted from photoprotective processes rather than photooxidative damage to PSII reaction centres. Stomatal conductance (Gs) was reduced, but this did not increase the stomatal limitation to photosynthesis. Changes in Gs were not correlated with changes in leaf ABA concentration.

 Known differences in phytoplasmal aggressiveness were correlated with degrees of inhibition of photosynthesis and occurence of photoinhibition. AshY phytoplasmas appear to cause metabolic perturbations associated with localized accumulation or multiplication of the pathogen in symptomatic leaves.

Abbreviations

A, net photosynthesis rate; Aa, net photosynthesis rate at ambient [CO2]; Amax, net photosynthesis rate at saturated [CO2]; AshY, ash yellows; Ci, intercellular [CO2]; Fo, Fm, Fv, minimal, maximum and variable fluorescence, respectively; F′m, Fs, maximal and steady state fluorescence in light‐adapted state; Fv/Fm, intrinsic efficiency of PSII; Gs, stomatal conductance; Jmax, maximum noncyclic electron transport; Ls, stomatal limitation; ΦPSII, quantum yield of PSII; qNP, nonphotochemical quenching coefficient; RuBP, ribulose‐1,5‐biophosphate; Vcmax, maximum rate of carboxylation of Rubisco; vpd, leaf‐to‐air vapor pressure deficit; WAG, week after grafting.
Cold adaptation in Arctic and Antarctic fungi
Authors: Robinson Clare H.
Published: March 2003

Growth and activity at low temperatures and possible physiological and ecological mechanisms underlying survival of fungi isolated from the cold Arctic and Antarctic are reviewed here. Physiological mechanisms conferring cold tolerance in fungi are complex; they include increases in intracellular trehalose and polyol concentrations and unsaturated membrane lipids as well as secretion of antifreeze proteins and enzymes active at low temperatures. A combination of these mechanisms is necessary for the psychrotroph or psychrophile to function. Ecological mechanisms for survival might include cold avoidance; fungal spores may germinate annually in spring and summer, so avoiding the coldest months. Whether spores survive over winter or are dispersed from elsewhere is unknown. There are also few data on persistence of basidiomycete vs microfungal mycelia and on the relationship between low temperatures and the predominance of sterile mycelia in tundra soils. Acclimation of mycelia is a physiological adaptation to subzero temperatures; however, the extent to which this occurs in the natural environment is unclear. Melanin in dark septate hyphae, which predominate in polar soils, could protect hyphae from extreme temperatures and play a significant role in their persistence from year to year.
Biology of mycorrhizal associations of epacrids (Ericaceae)
Authors: Cairney John W. G. , Ashford Anne E.
Published: March 2003

Epacrids, a group of southern hemisphere plants formerly considered members of the separate family Epacridaceae, are in fact most closely allied to the Vaccinioid tribe (Ericaceae). Epacrids and other extant ericoid mycorrhiza‐forming plants appear to have a monophyletic origin. In common with many Ericaceae they form ericoid mycorrhizas. ITS sequence data indicate that the fungi forming ericoid mycorrhizas with epacrids and other extant Ericaceae are broadly similar, belonging to a poorly defined group of ascomycetes with phylogenetic affinities to Helotiales. The basic development and structure of ericoid mycorrhizal infections in epacrids is similar to other Ericaceae. However, data are limited on the structure and physiology of both hair roots and ericoid mycorrhizas for all Ericaceae. Relatively little is known about the functional significance of ericoid mycorrhizas in epacrids in southern hemisphere habitats that are often poor in organic matter accumulation. However the abilities of fungal endophytes of epacrids to utilize organic N and P substrates equal those of endophytes from northern hemisphere heathland plant hosts. Investigations using 15N/13C‐labelled organic N substrates suggest that mycorrhizal endophytes are important, at least, to the N nutrition of their epacrid hosts in some habitats.

Contents

Summary
305

I.
Epacrid plant hosts
306

II.
Evolution of ericoid mycorrhizas in epacrids
306

III.
Epacrid hair roots and their mycorrhizal associations
307

IV.
Seasonality and incidence of mycorrhizal infection
310

V.
Structure and development of mycorrhizal associations
311

VI.
Nature of the mycorrhizal fungal endophytes
315

VII.
Community and population biology of mycorrhizal endophytes
318

VIII.
Functional aspects of mycorrhizas in epacrids
319

IX.
Conclusions
322

Acknowledgements
322

References
322
Biodegradation of linuron in a Phaseolus bioassay detected by chlorophyll fluorescence
Authors: Hulsen Kris , Top Eva M. , Höfte Monica
Published: March 2003

• Measuring chlorophyll fluorescence of sensitive indicator plants is a promising approach to follow microbial degradation of the photosystem II (PSII) inhibiting herbicide linuron in a plant–microbial bioassay.

• Both pulse amplitude modulation (PAM) fluorimetry and a stroboscope‐based Chla fluorescence imaging system were used to monitor the phytotoxic effect of linuron applied to bean (Phaseolus vulgaris) plants.

• Inoculation of a hydroponic model system with a linuron‐degrading microbial consortium mostly neutralized the phytotoxic effect of the linuron, applied at 0.1 mg l−1 and 1 mg l−1. This indicated that the inoculum was even able to degrade linuron at substrate concentrations (0.1 mg l−1) that were not detectable by HPLC analysis. The bioprotective effect of the inoculum was also demonstrated when 5 mg l−1 of linuron was spiked into a soil substrate.

• This is the first report on the use of chlorophyll fluorescence to demonstrate biodegradation. This method is particularly suited for the detection of low linuron concentrations and could probably also be used for other xenobiotics interfering with photosynthesis.
Cenococcum geophilumpopulations show a high degree of genetic diversity in beech forests
Authors: Jany Jean‐Luc , Garbaye Jean , Martin Francis
Published: March 2003

• The asexual ectomycorrhizal fungusCenococcum geophilum, known for its wide host and habitat range, has been suggested to provide isolate‐dependant drought protection to fine roots. However, little is known about its genetic structure at the fine scale.

• Genetic diversity and population structure ofC. geophilumat the regional and stand scales was surveyed in five beech (Fagus silvatica) forests in northeastern France. The stands were selected for their contrasting climatic and edaphic features to assess the effect of environmental factors on population structure.

• The genetic diversity ofC. geophilumwas estimated using RAPD, PCR/RFLP of the rDNA internal transcribed spacer (ITS) and PCR/RFLP and sequencing of an anonymous sequence characterized amplified region (SCAR) on ectomycorrhizas and sclerotia‐derived mycelial cultures.

• A high degree of genetic diversity was observed between and within beech stands inC. geophilumpopulations. These results suggest the occurrence of a high rate of mitotic or meiotic recombination and an effect of stand features on population structure.
Biochemical and molecular characterization of NADP‐glutamate dehydrogenase from the ectomycorrhizal fungus Tuber borchii
Authors: Vallorani Luciana , Polidori Emanuela , Sacconi Cinzia , Agostini Deborah , Pierleoni Raffaella , Piccoli Giovanni , Zeppa Sabrina , Stocchi Vilberto
Published: March 2003

• NADP‐glutamate dehydrogenase (NADP‐GDH) from Tuber borchii was purified and the corresponding gene was cloned in order to elucidate the physiological role of the enzyme in this ectomycorrhizal fungus.

• NADP‐GDH was purified using an anion‐exchange column followed by affinity chromatography. The complete gene was cloned from a 30‐d‐old‐mycelium cDNA library and characterized.

• T. borchii NADP‐GDH appears to be physically and kinetically similar to those from other fungi and the deduced amino acid sequence of the gdh gene showed a significant similarity to other fungal NADP‐dependent GDHs. Biochemical and Northern blotting analyses carried out with mycelia grown on different nitrogen sources clearly showed that the regulation of T. borchii NADP‐GDH in response to different nitrogen sources was markedly different from the responses of the NADP‐GDHs of other ascomycetes. Northern blotting analyses highlighted that the gdh gene was also expressed in the symbiotic phase.

• The biochemical and molecular data suggest that the fungal NADP‐GDH contributes to the primary nitrogen metabolism in the ectomycorrhizal tissues.
Extramatrical ectomycorrhizal mycelium contributes one‐third of microbial biomass and produces, together with associated roots, half the dissolved organic carbon in a forest soil
Authors: Högberg Mona N. , Högberg Peter
Published: March 2003

• A large‐scale tree‐girdling experiment enabled estimates in the field of the contribution of extramatrical mycelium of ectomycorrhizal (ECM) fungi to soil microbial biomass and by ECM roots and fungi to production of dissolved organic carbon (DOC).

• Tree‐girdling was made early (EG) or late (LG) during the summer to terminate the flow of photosynthate to roots and ECM fungi. Determination of microbial C (Cmicr) and microbial N in root‐free organic soil was performed by using the fumigation–extraction technique; extractable DOC was determined on unfumigated soil.

• Soil Cmicr was 41% lower on LG than on control plots 1 month after LG, whereas at the same time (that is, 3 months after EG), the Cmicr was 23% lower on EG than on control plots. Extractable DOC was 45% lower on girdled plots than control plots.

• Our results, which are of particular interest as they were obtained directly in the field, clearly demonstrate the important contribution by extramatrical ECM mycelium to soil microbial biomass and by ECM roots to the production of DOC, a carbon source for other microbes.
Linking photorespiration, monoterpenes and thermotolerance in Quercus
Authors: Peñuelas Josep , Llusià Joan
Published: March 2003

The functions of two important plant processes, photorespiration and monoterpene production remain controversial. Here, we investigated one possible function, that of protection of plants from photodamage at high temperatures.

Fluorescence, reflectance, monoterpene concentrations and visual leaf damage were measured in Quercus ilex
seedlings exposed to temperature increases from 25 to 50°C (in 5°C steps) under photorespiratory (21% O
2
) or nonphotorespiratory (2% O
2 ) atmospheres, and under control or terpene fumigation conditions.

Lower variable to maximum fluorescence ratio (Fv : Fm: potential photochemical efficiency of photosystem II, PSII) and electron transport rate (ETR) were found in nonphotorespiratory conditions at temperatures greater than 35°C. Monoterpene concentrations were also lower, and leaf damage greater, in the low O 2 atmospheres. Monoterpene fumigation, which increased the foliar terpene concentrations by two‐ to four‐fold, increased the photochemical efficiency between 35°C and 50°C, and decreased leaf damage, only under the nonphotorespiratory conditions.

These results provide evidence that: photorespiration decreases photodamage, especially at high temperatures; photorespiration increases monoterpene production; plants are able to acquire exogenous monoterpenes and the acquisition response to temperature follows the stomatal conductance response; and monoterpenes can replace photorespiration in protection from photodamage at high temperatures, possibly by scavenging oxygen‐reactive species, but they do not provide additional thermotolerance.
Morphogenetic modifications induced by Pseudomonas fluorescens A6RI and Glomus mosseae BEG12 in the root system of tomato differ according to plant growth conditions
Authors: Gamalero E. , Martinotti M. G. , Trotta A. , Lemanceau P. , Berta G.
Published: March 2003

The ability of fluorescent pseudomonads and glomalean fungi to promote plant growth has been reported many times. However, little is known of their effects on root morphogenesis. Growth and root morphogenesis were compared in tomato ( Lycopersicon esculentum
) plants inoculated or not with a model strain of
Pseudomonas fluorescens
(A6RI) or with the arbuscular mycorrhizal fungus
Glomus mosseae (BEG12).

Plants were cultivated in a sandy‐loam soil mixed with sand at two different ratios (2 : 1 and 1 : 2), in gnotobiotic conditions. Plant growth was evaluated by measuring root and shoot fresh weight, and various morphometric parameters were compared.

Growth of control plants was less in the 1 : 2 than in the 2 : 1 soil : sand mixture, and root morphogenesis was also significantly altered by soil:sand mixture. P. fluorescens
A6RI promoted plant growth and increased total root length, surface area and volume in the more fertile soil:sand mixture (2 : 1) whereas
G. mosseae BEG12 did the same in the less fertile soil : sand mixture (1 : 2).

The relevance of differences between the two types of organisms in relation to the environmental conditions favourable for the expression of their beneficial effects is discussed in the context of microbial inoculation.
Poikilohydry and homoihydry: antithesis or spectrum of possibilities?
Authors: Proctor Michael C. F. , Tuba Zoltán
Published: March 2003

Plants have followed two principal (and contrasting) strategies of adaptation to the irregular supply of water on land, which are closely bound up with scale. Vascular plants evolved internal transport from the soil to the leafy canopy (but their ‘homoihydry’ is far from absolute, and some are desiccation tolerant (DT)). Bryophytes depended on desiccation tolerance, suspending metabolism when water was not available; their cells are generally either fully turgid or desiccated. Desiccation tolerance requires preservation intact through drying–re‐wetting cycles of essential cell components and their functional relationships, and controlled cessation and restarting of metabolism. In many bryophytes and some vascular plants tolerance is essentially constitutive. In other vascular plants (particularly poikilochlorophyllous species) and some bryophytes tolerance is induced by water stress. Desiccation tolerance is adaptively optimal on hard substrates impenetrable to roots, and on poor dry soils in seasonally dry climates. DT vascular plants are commonest in warm semiarid climates; DT mosses and lichens occur from tropical to polar regions. DT plants vary widely in their inertia to changing water content. Some mosses and lichens dry out and recover within an hour or less; vascular species typically respond on a time scale of one to a few days.

Contents

Summary
327

I.
Introduction
328

II.
The soil–plant–atmosphere continuum
329

III.
Desiccation‐tolerant plants: taxonomic distribution and functional characteristics
331

IV.
Anatomical and physiological requirements and implications of desiccation tolerance
333

V.
Time‐scale considerations and ecological adaptation
340

VI.
Conclusion
344

Acknowledgements
344

References
344
Phosphorus acquisition and use: critical adaptations by plants for securing a nonrenewable resource
Authors: Vance Carroll P. , Uhde‐Stone Claudia , Allan Deborah L.
Published: March 2003

Phosphorus (P) is limiting for crop yield on > 30% of the world's arable land and, by some estimates, world resources of inexpensive P may be depleted by 2050. Improvement of P acquisition and use by plants is critical for economic, humanitarian and environmental reasons. Plants have evolved a diverse array of strategies to obtain adequate P under limiting conditions, including modifications to root architecture, carbon metabolism and membrane structure, exudation of low molecular weight organic acids, protons and enzymes, and enhanced expression of the numerous genes involved in low‐P adaptation. These adaptations may be less pronounced in mycorrhizal‐associated plants. The formation of cluster roots under P‐stress by the nonmycorrhizal species white lupin (Lupinus albus), and the accompanying biochemical changes exemplify many of the plant adaptations that enhance P acquisition and use. Physiological, biochemical, and molecular studies of white lupin and other species response to P‐deficiency have identified targets that may be useful for plant improvement. Genomic approaches involving identification of expressed sequence tags (ESTs) found under low‐P stress may also yield target sites for plant improvement. Interdisciplinary studies uniting plant breeding, biochemistry, soil science, and genetics under the large umbrella of genomics are prerequisite for rapid progress in improving nutrient acquisition and use in plants.

Contents

I.
Introduction
424

II.
The phosphorus conundrum
424

III.
Adaptations to low P
424

IV.
Uptake of P
424

V.
P deficiency alters root development and function
426

VI.
P deficiency modifies carbon metabolism
431

VII.
Acid phosphatase
436

VIII.
Genetic regulation of P responsive genes
437

IX.
Improving P acquisition
439

X.
Synopsis
440
Factors involved in the learning of consumer studies
Authors: Byrne Mike S.
Published: March 2003

This study explored links between students’ psychological traits and their expressed preferences for learning approaches, and performance, on a consumer studies degree course. Measures to assess field independence, convergence–divergence and Perry position (a developmental classification based on students’ attitudes to knowledge and learning), and students’ preferences with regard to directed, group, project and practical learning approaches, were administered to 60 final‐year and 56 first‐year students on a consumer studies degree course. Perry position and a preference for a project learning approach were found to correlate most highly with overall performance. Field independence and convergence–divergence did not correlate at statistically significant levels with any element of final degree performance. As students proceeded through the course, they developed an enhanced view of a project learning approach and a diminished view of a group learning approach. On the basis of these findings, a number of recommendations for the teaching and learning consumer studies are put forward.
Children as consumers – snacking behaviour in primary school children
Authors: Bower John A. , Sandall Louise
Published: March 2003

Eighty‐four primary school children (the majority aged 7–8 years), from four schools, two in England and two in Scotland, were surveyed to identify snacking behaviour and the influences on perception and choice of snack foods. A questionnaire plus short interview with activity tasks was adopted, covering general snacking habits and a look at six specific groups of snacks comprising three of ‘unhealthy’ image and three with intermediate or fully ‘healthy’ image. The results showed that, for this age group, there was an overall preference for sweets, crisps and chocolate and less liking for fruit and cereal‐containing snacks. Attitudes to sensory properties showed that ‘taste’ was the main reason for snack choices, usually in spite of a ‘healthy’ image belief for the snacks. Choice was also dependent on parental influence and availability. Gender and relative socio‐economic level differences were minimal, but regional variations showed higher snacking frequency for the Scottish group, which also had fewer children preferring fruit. Meal patterns had little effect on snacking, but inclusion of a prepared meal at lunchtime may have reduced snacking frequency.
Evidence‐based librarianship: what might we expect in the years ahead?*
Authors: Eldredge Jonathan D.
Published: March 2003

Objective: To predict the possible accomplishments of the Evidence‐Based Librarianship (EBL) movement by the years 2005, 2010, 2015 and 2020.

Methods: Predictive. The author draws upon recent events, relevant historical events and anecdotal accounts to detect evidence of predictable trends.

Results: The author develops a set of probable predictions for the development of EBL. Although incomplete evidence exists, some trends still seem discernible.

Conclusion: By 2020, EBL will have become indistinguishable from mainstream health sciences librarianship/informatics practices.
Surfing for health: user evaluation of a health information website. Part one: background and literature review
Authors: Williams Peter , Nicholas David , Huntington Paul , McLean Fiona
Published: March 2003

The Government in Britain is set on using the Internet to expand the provision of health information to the general public. Concerns over the quality of the health information have preoccupied commentators and organizations rather than the way users interact with health information systems. This report examines the issues surrounding the provision of electronic health information, and describes an evaluation undertaken of a commercial health website—that of Surgerydoor (http://www.surgerydoor.co.uk/), and comprises two parts. Part one outlines the literature on electronic health information evaluation. It discusses quality issues, but also redresses the imbalance by exploring other evaluative perspectives. Part two describes an evaluation of a health information Internet site in terms of its usability and appeal, undertaken as part of a Department of Health funded study on the impact of such systems.
The US National Library of Medicine in the 21st century: expanding collections, nontraditional formats, new audiences
Authors: Lacroix Eve‐Marie , Mehnert Robert
Published: March 2003

From the early 1960s, the US National Library of Medicine (NLM) has been a leader in applying computer technology to accomplish traditional bibliographic and reference functions. medline, in the early 1970s, was the first large‐scale online medical bibliographic reference system. That role has been altered by today's Web environment, which has increased the number and extent of NLM services and the audience for them. The NLM has formally declared that it will seek to serve the general public after over a century of serving the library and medical communities exclusively. In the last several years, many new services have been introduced to fulfil this mandate, including medlineplus and ClinicalTrials.gov. Also a part of the NLM's vision for the 21st century is the need to ensure that the proliferating forms of electronic health information—bibliographic, full text, graphic, audiovisual—are captured and preserved for posterity. A national library such as the NLM has as much an archival responsibility for this electronic information as for centuries‐old printed and manuscript historical treasures.
Structural and Functional Organization of the Gene Encoding the Human Thyrotropin‐Releasing Hormone Receptor
Authors: Matre Vilborg , Høvring Per Ivar , Ørstavik Sigurd , Frengen Eirik , Rian Edith , Velickovic Zlatibor , Murray‐McIntosh Rosalind P. , Gautvik Kaare M.
Published: March 2003

Abstract : The thyrotropin‐releasing hormone (TRH) receptor (TRHR)
is widely distributed throughout the central and peripheral nervous systems.
In addition to its role in controlling the synthesis and secretion of
thyroid‐stimulating hormone and prolactin from the anterior pituitary, TRH is
believed to act as a neurotransmitter as well as a neuromodulator. We have
isolated genomic λ and P1‐derived artificial chromosome clones encoding
the human TRHR. The gene was found to be 35 kb with three exons and two
introns. A 541‐bp intron 1 (‐629 to ‐89 relative to the translation start
site) is conserved between human and mouse. A large intron 2 of 31 kb disrupts
the open reading frame (starting in position +790) in the sequence encoding
the supposed junction between the third intracellular loop and the putative
sixth transmembrane domain. A similar intron was found in chimpanzee and sheep
but not in rat and mouse. Promoter analysis of upstream regions demonstrated
cell type‐specific reporter activation, and sequencing of 2.5 kb of the
promoter revealed putative cis‐acting regulatory elements for several
transcription factors that may contribute to the regulation of the
TRHR gene expression. Functional analysis of potential response
elements for the anterior pituitary‐specific transcription factor Pit‐1
revealed cell type‐specific binding that was competed out with a Pit‐1
response element from the GH gene promoter.
Dopamine D2‐Receptor Isoforms Expressed in AtT20 Cells InhibitQ‐Type High‐Voltage‐Activated Ca2+ Channels via a Membrane‐Delimited Pathway
Authors: Wolfe Shannyn E. , Howard Daniel E. , Schetz John A. , Cheng Caroline J. , Webber Robert , Beatty Diane M. , Chronwall Bibie M. , Morris Stephen J.
Published: March 2003

Abstract : Dopamine D2 receptors both acutely and
chronically inhibit high‐voltage‐activated Ca2+ channels (HVA‐CCs).
Two alternatively spliced isoforms, D2L (long) and D2S
(short), are expressed at high levels in rat pituitary intermediate lobe
melanotropes but are lacking in anterior lobe corticotropes. We stably
transfected D2L and D2S into corticotrope‐derived AtT20
cells. Both isoforms coupled to inhibition of Q‐type calcium channels through
pertussis toxin‐sensitive G proteins. Thus, we have created a model system in
which to study the kinetics of D2‐receptor regulation of
Ca2+ channels. Rapid inhibition of HVA‐CCs was characterized using
a novel fluorescence video imaging technique for the measurement of
millisecond kinetic events. We measured the time elapsed (lag time) between
the arrival of depolarizing isotonic 66 mM K+, sensed by
fluorescence from included carboxy‐X‐rhodamine (CXR), and the beginning of
increased intracellular Ca2+ levels (sensed by changes in indo 1
fluorescence ratio). The lag time averaged 350‐550 ms, with no significant
differences among cell types. Addition of the D2‐agonist quinpirole
(250 μM) to the K+/CXR solution significantly increased
the lag times for D2‐expressing cells but did not alter the lag
time for AtT20 controls. The increased lag times for D2L ‐ and
D2S‐transfected cells suggest that at least a fraction of the
Ca2+ channels was inhibited within the initial 350‐550 ms. As this inhibition time is too fast for a multistep second messenger pathway, we conclude that inhibition occurs via a membrane‐delimited diffusion mechanism.
Pivotal Role of Mitochondrial Calcium Uptake in Neural Cell Apoptosis and Necrosis
Authors: Kruman Inna I. , Mattson Mark P.
Published: March 2003

Abstract : Perturbed cellular calcium homeostasis has been
implicated in both apoptosis and necrosis, but the role of altered
mitochondrial calcium handling in the cell death process is unclear. The
temporal ordering of changes in cytoplasmic ([Ca2+]C) and
intramitochondrial ([Ca2+]M) calcium levels in relation to
mitochondrial reactive oxygen species (ROS) accumulation and membrane
depolarization (MD) was examined in cultured neural cells exposed to either an
apoptotic (staurosporine ; STS) or a necrotic (the toxic aldehyde
4‐hydroxynonenal ; HNE) insult. STS and HNE each induced an early increase of
[Ca2+]C followed by delayed increase of [Ca2+]M.
Overexpression of Bcl‐2 blocked the elevation of [Ca2+]M and the MD
in cells exposed to STS but not in cells exposed to HNE. The cytoplasmic
calcium chelator BAPTA‐AM and the inhibitor of mitochondrial calcium uptake
ruthenium red prevented both apoptosis and necrosis. STS and HNE each induced
mitochondrial ROS accumulation and MD, which followed the increase of
[Ca2+]M. Cyclosporin A prevented both apoptosis and necrosis,
indicating critical roles for MD in both forms of cell death. Caspase
activation occurred only in cells undergoing apoptosis and preceded increased
[Ca2+]M. Collectively, these findings suggest that mitochondrial calcium overload is a critical event in both apoptotic and necrotic cell death.
A 127‐kDa Protein (UV‐DDB) Binds to the Cytoplasmic Domain of the Alzheimer's Amyloid Precursor Protein
Authors: Watanabe Takuo , Sukegawa Jun , Sukegawa Izumi , Tomita Susumu , Iijima Ko‐ichi , Oguchi Shinobu , Suzuki Toshiharu , Nairn Angus C. , Greengard Paul
Published: March 2003

Abstract : Alzheimer amyloid precursor protein (APP) is an integral
membrane protein with a short cytoplasmic domain of 47 amino acids. It is
hoped that identification of proteins that interact with the cytoplasmic
domain will provide new insights into the physiological function of APP and,
in turn, into the pathogenesis of Alzheimer's disease. To identify proteins
that interact with the cytoplasmic domain of APP, we employed affinity
chromatography using an immobilized synthetic peptide corresponding to
residues 645‐694 of APP695 and identified a protein of ~130 kDa in
rat brain cytosol. Amino acid sequencing of the protein revealed the protein
to be a rat homologue of monkey UV‐DDB (UV‐damaged DNA‐binding protein,
calculated molecular mass of 127 kDa). UV‐DDB/p127 co‐immunoprecipitated with
APP using an anti‐APP antibody from PC12 cell lysates. APP also
co‐immunoprecipitated with UV‐DDB/p127 using an anti‐UV‐DDB/p127 antibody.
These results indicate that UV‐DDB/p127, which is present in the cytosolic
fraction, forms a complex with APP through its cytoplasmic domain. In vitro
binding experiments using a glutathione S‐transferase‐APP cytoplasmic domain fusion protein and several mutants indicated that the YENPTY motif within the APP cytoplasmic domain, which is important in the internalization of APP and amyloid β protein secretion, may be involved in the interaction between UV‐DDB/p127 and APP.
Role of Protein Kinase C (PKC) in Agonist‐Induced α‐Opioid Receptor Down‐Regulation
Authors: Kramer H. Kenneth , Simon Eric J.
Published: March 2003

Abstract : Phosphorylation of specific amino acid residues is
believed to be crucial for the agonist‐induced regulation of several G
protein‐coupled receptors. This is especially true for the three types of
opioid receptors (μ, δ, and α), which contain consensus sites
for phosphorylation by numerous protein kinases. Protein kinase C (PKC) has
been shown to catalyze the in vitro phosphorylation of μ‐ and
δ‐opioid receptors and to potentiate agonist‐induced receptor
desensitization. In this series of experiments, we continue our investigation
of how opioid‐activated PKC contributes to homologous receptor down‐regulation
and then expand our focus to include the exploration of the mechanism(s) by
which μ‐opioids produce PKC translocation in SH‐SY5Y neuroblastoma cells.
[dAla2,N‐Me‐Phe4,Gly‐ol]enkephalin
(DAMGO)‐induced PKC translocation follows a time‐dependent and biphasic
pattern beginning 2 h after opioid addition, when a pronounced translocation
of PKC to the plasma membrane occurs. When opioid exposure is lengthened to
>12 h, both cytosolic and particulate PKC levels drop significantly below
those of control‐treated cells in a process we termed “reverse
translocation.” The opioid receptor antagonist naloxone, the PKC
inhibitor chelerythrine, and the L‐type calcium channel antagonist nimodipine
attenuated opioid‐mediated effects on PKC and μ‐receptor down‐regulation,
suggesting that this is a process partially regulated by
Ca2+‐dependent PKC isoforms. However, chronic exposure to phorbol
ester, which depletes the cells of diacylglycerol (DAG) and
Ca2+‐sensitive PKC isoforms, before DAMGO exposure, had no effect
on opioid receptor down‐regulation. In addition to expressing conventional
(PKC‐α) and novel (PKC‐ε) isoforms, SH‐SY5Y cells also contain a
DAG‐and Ca2+‐independent, atypical PKC isozyme (PKC‐ξ), which does not decrease in expression after prolonged DAMGO or phorbol ester treatment. This led us to investigate whether PKC‐ξ is similarly sensitive to activation by μ‐opioids. PKC‐ξ translocates from the cytosol to the membrane with kinetics similar to those of PKC‐α and ε in response to DAMGO but does not undergo reverse translocation after longer exposure times. Our evidence suggests that direct PKC activation by μ‐opioid agonists is involved in the processes that result in μ‐receptor down‐regulation in human neuroblastoma cells and that conventional, novel, and atypical PKC isozymes are involved.
Pathogenesis of Inclusion Bodies in (CAG)n/Qn‐Expansion Diseases with Special Reference to the Role of Tissue Transglutaminase and to Selective Vulnerability
Authors: Cooper Arthur J. L. , Sheu Kwan‐Fu Rex , Burke James R. , Strittmatter Warren , Gentile Vittorio , Peluso Gianfranco , Blass John P.
Published: March 2003

Abstract : At least eight neurodegenerative diseases, including
Huntington disease, are caused by expansions in (CAG)n repeats in
the affected gene and by an increase in the size of the corresponding
polyglutamine domain in the expressed protein. A hallmark of several of these
diseases is the presence of aberrant, proteinaceous aggregates in the nuclei
and cytosol of affected neurons. Recent studies have shown that expanded
polyglutamine (Qn) repeats are excellent glutaminyl‐donor
substrates of tissue transglutaminase, and that the substrate activity
increases with increasing size of the polyglutamine domain. Tissue
transglutaminase is present in the cytosol and nuclear fractions of brain
tissue. Thus, the nuclear and cytosolic inclusions in Huntington disease may
contain tissue transglutaminase‐catalyzed covalent aggregates. The
(CAG)n/Qn‐expansion diseases are classic examples of
selective vulnerability in the nervous system, in which certain
cells/structures are particularly susceptible to toxic insults. Quantitative
differences in the distribution of the brain transglutaminase(s) and its
substrates, and in the activation mechanism of the brain transglutaminase(s),
may explain in part selective vulnerability in a subset of neurons in
(CAG)n‐expansion diseases, and possibly in other neurodegenerative disease. If tissue transglutaminase is found to be essential for development of pathogenesis, then inhibitors of this enzyme may be of therapeutic benefit.