bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization and identification of black alder ectomycorrhizas by PCR/RFLP analyses of the rDNA internal transcribed spacer (ITS)
Authors: PRITSCH K. , BOYLE H. , MUNCH J. C. , BUSCOT F. 
Published: March 2003

summaryThe identity of black alder (Alnus glutinosa (L.) Gaertn.) ectomycorrhizas was investigated using PCR/RFLP analysis of the ITS region from 16 morphotypes sampled at a 60‐yr‐old black alder stand. A comparison was made with restriction patterns from sporocarps of 28 mycobionts, of which 16 originated from the same stand, the remaining 12 came from two geographically distant alder stands. Eight of the mycorrhizal types could thus be identified, whereas eight mycorrhizal types remained unidentified. The identified mycorrhizas belonged to the genera Russula, Lactarius, Naucoria and Cortinarius. Four of the identified ectomycorrhizal types had identical PCR/RFLP profiles to corresponding fruit bodies from all investigated stands with no detectable intraspecific variation, despite the geographical distance of c.300 km between the sampling locations. By contrast, intraspecific variation between sporocarps from the different locations was detected in Paxillus rubicundulus, mycorrhizas of which were not found. The diversity of fruiting alder mycobionts at the main experimental plot only partly matched the diversity observed from mycorrhizas when comparing their PCR/RFLP profiles. The results are discussed regarding sampling techniques, PCR/RFLP analyses and ecological aspects.
Elevated CO2 enhances below‐ground C allocation in three perennial grass species at different levels of N availability
Authors: COTRUFO M. F. , GORISSEN A. 
Published: March 2003

summaryThree perennial grass species, Lolium perenne L., Agrottis capillaris L. and Festuca uvina L., were homogeneously labelled in phytotrons with 14CO2 at two CO2 concentrations (350 and 700μl l−1). Plants were grown under two nitrogen regimes: one with a minor addition of 8 kg N ha−1, the other with an addition of 278 kg N ha−1. Carbon allocation over the different compartments of the plant/soil systems was measured: shoots, roots, rhizosphere soil (soil solution, microbial biomass and soil residue), and bulk soil. Elevated CO., increased total net 14C recovery in all species by 14%, and significantly enhanced the below‐ground 14C allocation by 26%, this enhancement was 24%, 39% and 21 % for root, rhizosphere soil and bulk soil, respectively. Within the rhizosphere soil, the 14C amounts in the soil solution (+ 69%) and soil residue (+ 49%,) increased significantly. Total microbial biomass‐C in the rhizosphere soil was also increased (15 %) by the elevated CO2 treatment, but only in proportion to the increased root mass. No interactions were observed between the elevated CO2, and N treatments. The N treatment increased total net 14C recovery by more than 300% and 14C was preferentially allocated to the shoots, leading to a significant increase in shoot‐to‐root ratio. However, N fertilization also increased (+111%) the absolute amount of 14C in soil. The three species behaved differently, but no interactions were observed between CO2 treatment and plant species. These results show that elevated CO2 induces an increased C input into soil for all three grass species at both N levels. However, the highest absolute amounts were found in the soils of the fastest growing species and at the highest N level.
Regulation of photosynthetic pigments in micro‐algae by multiple environmental factors: a dynamic balance hypothesis
Authors: KANA TODD M. , GEIDER RICHARD J. , CRITCHLEY CHRISTA 
Published: March 2003

summaryEnvironmental effects on the concentration of photosynthetic pigments in micro‐algae can be explained by dynamics of photosystem synthesis and deactivation. A model that couples photosystem losses to the relative cellular rates of energy harvesting (light absorption) and assimilation predicts optimal concentrations of light‐harvesting pigments and balanced energy flow under environmental conditions that affect light availability and metabolic rates. Effects of light intensity, nutrient supply and temperature on growth rate and pigment levels were similar to general patterns observed across diverse micro‐algal taxa. Results imply that dynamic behaviour associated with photophysical stress, and independent of gene regulation, might constitute one mechanism for photo‐acclimation of photosynthesis.
The atmospheric budget of oxidized nitrogen and its role in ozone formation and deposition
Authors: FOWLER DAVID , FLECHARD CHRIS , SKIBA UTE , COYLE MHAIRI , CAPE J. NEIL 
Published: March 2003

Emissions of reactive oxidized nitrogen (NO and NO2), collectively known as NOx, from human activities are c. 21 Tg N annually, or 70% of global total emissions. They occur predominantly in industrialized regions, largely from fossil fuel combustion, but also from increased use of N fertilizers. Soil emissions of NO not only make an important contribution to global totals, but also play a part in regulating the dry deposition of NO and NO2 (NOx) to plant canopies. Soil microbial production of NO leads to a soil ‘compensation point’ for NO deposition or emission, which depends on soil temperature, N and water status. In warm conditions, the net emission of NOx from plant canopies contributes to the photochemical formation of ozone. Moreover, the effect of NOx emissions from soil is to reduce net rates of NO2 deposition to terrestrial surfaces over large areas.Increasing anthropogenic emissions of NOx have led to an approximate doubling in surface O3 concentrations since the last century. NOx acts as a catalyst for the production of O3 from volatile organic compounds (VOCs). Paradoxically, emission controls on motor vehicles might lead to increases in O3 concentrations in urban areas.Removal of NO and NO2 by dry deposition is regulated to some extent by soil production of NO; the major sink for NO2 is stomatal uptake. Long‐term flux measurements over moorland in Scotland show very small deposition rates for NO2 at night and before mid‐day of 1–4 ng NO2‐N m−2 s−1, and similar emission rates during afternoon. The bi‐directional flux gives 24‐h average deposition velocities of only 1–2 mm s−1, and implies a long life‐time for NOx due to removal by dry deposition.Rates of removal of O3 at the ground are also influenced by stomatal uptake, but significant non‐stomatal uptake occurs at night and in winter. Measurements above moorland showed 40% of total annual flux was stomatal, with 60% non‐stomatal, giving nocturnal and winter deposition velocities of 2–3 mm s−1 and daytime summer values of 10 mm s−1. The stomatal uptake is responsible for adverse effects on vegetation. The critical level for O3 exposure (AOT40) is used to derive a threshold O3 stomatal flux for wheat of 0·5 μg m−2 s−1. Use of modelled stomatal fluxes rather than exposure might give more reliable estimates of yield loss; preliminary calculations suggest that the relative grain yield reduction (%) can be estimated as 38 times the stomatal ozone flux (g m−2) above the threshold, summed over the growing season.
Tansley Review No. 107. Heterocyst and akinete differentiation in cyanobacteria
Authors: ADAMS DAVID G. , DUGGAN PAULA S. 
Published: March 2003

Summary 3I. introduction 4II. the cyanobacteria 7III. the heterocyst 91. Function and metabolism 92. Heterocyst structure 12(a) Overview 12(b) The polysaccharide (homogeneous) layer 12(c) The glycolipid (laminated) layer 12(d) The septum and microplasmodesmata 123. Nitrogen regulation and heterocyst development 124. Heterocyst development 13(a) The proheterocyst 13(b) Proteolysis associated with heterocyst development 14(c) RNA polymerase sigma factors 14(d) Developmental regulation of heterocyst cell wall and nitrogenase gene expression 14(e) Genome rearrangements associated with heterocyst development 155. Genes essential for heterocyst development 15(a) hetR 15(b) Protein phosphorylation and the regulation of hetR activity 16(c) hetR in nonheterocystous cyanobacteria 16(d) Other heterocyst‐specific genes 166. Heterocyst spacing 18(a) Patterns of heterocyst differentiation 18(b) Genes involved in heterocyst spacing 18(c) Disruption of heterocyst pattern 187. Filament fragmentation and the regression of developing heterocysts 208. The nature of the heterocyst inhibitor 209. Cell selection during differentiation and pattern formation 20(a) Cell division 20(b) DNA replication and the cell cycle 21(c) Competition 2110. Models for heterocyst differentiation and pattern control 21IV. the akinete 231. Properties of akinetes 232. Structure, composition and metabolism 243. Relationship to heterocysts 244. Factors that influence akinete differentiation 245. Extracellular signals 256. Akinete germination 257. Genes involved in akinete differentiation 26V. conclusion 26Acknowledgements 27References 28Cyanobacteria are an ancient and morphologically diverse group of photosynthetic prokaryotes. They were the first organisms to evolve oxygenic photosynthesis, and so changed the Earth's atmosphere from anoxic to oxic. As a consequence, many nitrogen‐fixing bacteria became confined to suitable anoxic environmental niches, because the enzyme nitrogenase is highly sensitive to oxygen. However, in the cyanobacteria a number of strategies evolved that protected nitrogenase from oxygen, including a temporal separation of oxygenic photosynthesis and nitrogen fixation and, in some filamentous strains, the differentiation of a specialized cell, the heterocyst, which provided a suitable microaerobic environment for the functioning of nitrogenase. The evolution of a spore‐like cell, the akinete, almost certainly preceded that of the heterocyst and, indeed, the akinete may have been the ancestor of the heterocyst. Cyanobacteria have the capacity to differentiate several additional cell and filament types, but this review will concentrate on the heterocyst and the akinete, emphasizing the differentiation and spacing of these specialized cells.
Sap velocity and canopy transpiration in a sweetgum stand exposed to free‐air CO2 enrichment (FACE)
Authors: Wullschleger Stan D. , Norby Richard J. 
Published: March 2003

Summary

Canopy transpiration rates, as a major component of forest hydrologic budgets, are reported for 12‐yr‐old sweetgum (Liquidambar styraciflua) trees growing in a free‐air CO2 enrichment (FACE) study in eastern Tennessee, USA.
The compensated heat‐pulse technique was used to measure rates of sap velocity, and stand transpiration was estimated as a function of measured sap velocity, total stand sapwood area and the fraction of sapwood functional in water transport.
Sap velocity averaged 13% less for trees in elevated compared with ambient CO2 concentration. Stand transpiration reached 5.6 and 4.4 mm d−1 for the ambient and elevated CO2 treatments, respectively. Stratification of the data showed that significant differences in stand transpiration were observed between ambient and elevated CO2 only at mean daily radiation levels > 400 J m−2 s−1 and at vapor pressure deficits > 1.0 kPa.
These data illustrate that while elevated CO2 may reduce canopy transpiration, the apparent dependency of such an effect on prevailing weather makes detecting a CO2‐induced impact on forest water use difficult.
Modelling the response of wheat canopy assimilation to atmospheric CO2 concentrations
Authors: Rodriguez D. , Ewert F. , Goudriaan J. , Manderscheid R. , Burkart S. , Weigel H. J. 
Published: March 2003

Summary

•  The predictive capacity of two simulation models with different degrees of complexity for the calculation of assimilate production, was tested at different time scales, using a data set of wheat grown in an open‐top‐chamber experiment at two CO2 concentrations.
•  Observed values of net canopy assimilation (Pn) were obtained from wheat plants grown at ambient (410 µmol mol−1) and elevated (680 µmol mol−1) CO2 mole fractions. Pn was simulated by using either simple multiple regression equations (AFRCWHEAT2) or by highly detailed calculations of leaf energy balances and the coupling of photosynthesis with stomatal conductance (LINTULCC2).
•  Irrespective of the developmental stage of the crop or variation in weather, the models accurately simulated canopy assimilation and growth. We conclude that the response of aboveground‐biomass production to elevated CO2 concentrations was explained primarily by the effects of CO2 on radiation‐use efficiency and assimilate production.
•  The models explained satisfactorily the daily course of Pn, its integrated daily totals, and the seasonally produced aboveground biomass, both at ambient and elevated CO2 concentrations. Specific problems in the simulations were identified and discussed.
Interpretation of bioassays in the study of interactions between soil organisms and plants: involvement of nutrient factors
Authors: Troelstra S. R. , Wagenaar R. , Smant W. , Peters B. A. M. 
Published: March 2003

Summary Increased plant growth in sterilized soil is usually ascribed to the elimination of (often unidentified) soil‐borne pathogens. Plant–soil bioassays are reported here for three dune soils and two plant species (Ammophila arenariaandCarex arenaria). Dynamics of plant growth, availability and uptake of nutrients were compared in sterilized (25 kGy gamma‐irradiation) vs control soils. Plant growth, availability and acquisition of nutrients, for example P, even when provided in apparent excess, were significantly enhanced in gamma‐irradiated calcareous dune sands. WithA. arenaria, the positive sterilization effect occurred independently of initial plant dry mass. The addition of extracts of planted soils toA. arenariagrowing in unsterilized sand caused an increase in root growth that could not be related to either nutrients or pathogens. Increased availability and acquisition of nutrients in sterilized soil may contribute to nonsterile : sterile ratios of plant growth that are < 1. Any ecological speculation involving the role of soil‐borne biological factors should be based on fully validated plant–soil bioassays, which account for nutritional or other nonpathogen‐related side‐effects induced by soil sterilization.
Species‐specific responses of a root‐ and shoot‐feeding insect to arbuscular mycorrhizal colonization of its host plant
Authors: Gange Alan C. 
Published: March 2003

Summary

The responses of root‐feeding black vine weevil (Otiorhynchus sulcatus) larvae and leaf‐feeding adults to colonization of strawberry (Fragaria x ananassa) plants by one or two species of arbuscular mycorrhizal fungi are reported here.
Glomus mosseae and Glomus fasciculatum were isolated from a commercial field and used to colonize strawberry plants, singly and in combination. Vine weevil larvae were reared on roots of colonized and uncolonized plants. When the larvae were mature, leaves from all plants, with and without larvae, were fed to adult weevils.
Colonization by either fungus reduced larval survival and biomass. However, colonization by both fungi had no effect on the larvae. These effects were manifested in changes in plant performance; weevil feeding decreased plant foliar and root biomass as well as runner production, but only when mycorrhizas were absent or inoculated together. Mycorrhizas also mitigated the effects of larval feeding on adult weevils.
The response of root‐feeding insects to arbuscular mycorrhizal colonization depends on which fungi are present in the root system. Furthermore, arbuscular mycorrhizal fungi might play a critical role in mitigating interactions between phytophagous insects.
Receptor serine/threonine protein kinases in signalling: analysis of the erecta receptor‐like kinase of Arabidopsis thaliana
Authors: Lease Kevin A. , Lau Nelson Y. , Schuster Robert A. , Torii Keiko U. , Walker John C. 
Published: March 2003

SummaryThe Arabidopsis ERECTA (ER) gene regulates elongation of above‐ground organs. ER encodes a member of the leucine‐rich repeats–receptor‐like protein kinases (LRR–RLK) gene family, with the predicted protein containing a signal peptide, 20 leucine‐rich repeats in the extracellular domain, a transmembrane domain, and a cytoplasmic serine/threonine protein kinase domain. The structural features of the predicted ER protein suggest its role in cell–cell signalling is through phosphorylating serine/threonine residues. Consistent with this hypothesis, in vitro protein kinase analysis indicates that ER is a functional serine/threonine protein kinase. Furthermore, a large‐scale genetic screen was conducted to analyse new mutations in the erecta gene; 16 new er alleles were isolated, all of which were recessive. Here we present the identification of molecular lesions of seven alleles of er, which suggests the hypothesis that ERECTA might employ a mode of action distinct from other RLKs such as Xa21 or CLAVATA1, which function in disease resistance and developmental pathways, respectively.
Calmodulin as a versatile calcium signal transducer in plants
Authors: Snedden Wayne A. , Fromm Hillel 
Published: March 2003

SummaryThe complexity of Ca2+ patterns observed in eukaryotic cells, including plants, has led to the hypothesis that specific patterns of Ca2+ propagation, termed Ca2+ signatures, encode information and relay it to downstream elements (effectors) for translation into appropriate cellular responses. Ca2+‐binding proteins (sensors) play a key role in decoding Ca2+ signatures and transducing signals by activating specific targets and pathways. Calmodulin is a Ca2+ sensor known to modulate the activity of many mammalian proteins, whose targets in plants are now being actively characterized. Plants possess an interesting and rapidly growing list of calmodulin targets with a variety of cellular roles. Nevertheless, many targets appear to be unique to plants and remain uncharacterized, calling for a concerted effort to elucidate their functions. Moreover, the extended family of calmodulin‐related proteins in plants consists of evolutionarily divergent members, mostly of unknown function, although some have recently been implicated in stress responses. It is hoped that advances in functional genomics, and the research tools it generates, will help to explain themultiplicity of calmodulin genes in plants, and to identify their downstream effectors. This review summarizes current knowledge of the Ca2+–calmodulin messenger system in plants and presents suggestions for future areas of research.

Contents

I.
Introduction
36

II.
CaM isoforms and CaM‐like proteins
37

III.
CaM‐target proteins
42

IV.
CaM and nuclear functions
46

V.
Regulation of ion transport
49

VI.
CaM and plant responses to environmental stimuli
52

VII.
Conclusions and future studies
58

Acknowledgements
59

References
59
O3uptake and drought stress effects on carbon acquisition of ponderosa pine in natural stands
Authors: Grulke NE , Preisler HK , Rose C , Kirsch J , Balduman L 
Published: March 2003

Summary• The effect of O3exposure or uptake on carbon acquisition (net assimilation (A) or gross photosynthesis (Pg)), with and without drought stress, is reported here in 40‐yr‐old‐ponderosa pine (Pinus ponderosa) trees.• Maximum daily gas exchange was measured monthly for 12 trees at four sites differing in pollutant exposure over two growing seasons with above‐ and below‐average annual precipitation. Gas exchange measures were estimated between sampling periods using a generalized additive regression model.• Both A andPggenerally declined with cumulative O3exposure or uptake at all sites. As a response variable,Pgwas slightly more sensitive thanAto cumulative O3exposure. As a metric, O3uptake vs exposure permitted slightly better statistical resolution of seasonal response between sites.• The effect of late summer drought stress was statistically significant only at the moderate pollution site, and combined synergistically with O3exposure or uptake to reducePg. The general additive model allows the user to define a deleterious level of cumulative O3exposure or uptake, and to quantitatively assess biological response.
Phospho‐imaging as a tool for visualization and noninvasive measurement of P transport dynamics in arbuscular mycorrhizas
Authors: Nielsen J. S. , Joner E. J. , Declerck S. , Olsson S. , Jakobsen I. 
Published: March 2003

Summary• A new method is described for monitoring hyphal 32P transport in compartmented, monoxenic mycorrhizal root cultures. Nondestructive time‐course measurements of P transport in hyphae were obtained by capturing digital autoradiograms on P‐imaging screens, and comparing with growth observed by optical scanning. 32P distribution measured by densitometry on the day of harvest closely agreed with values obtained by liquid scintillation counting after destructive harvest.• Virtually all labeled PO4 was absorbed by arbuscular mycorrhizal (AM) hyphae, but transfer to the roots appeared to be incomplete. P transport was not unidirectional towards the roots, as 32P was also transported from the root compartment to the hyphal compartment. Net P flux rates were calculated for hyphae crossing between compartments, taking bidirectional flow into account.• Amounts of transported P were poorly correlated with extra‐radical hyphal length and root d. wt, but highly correlated with the number of hyphae crossing the barrier separating the two compartments. Such correlations were highest when only hyphae with detectable protoplasmic streaming were considered.• The method was tested using radiolabeled P sources, H2PO4− and cytidine triphosphate (CTP), and the AM fungi, Glomus intraradices and G. proliferum. Fungal transport of 32P from CTP was much slower than from PO4 for both fungi.
Nitrogen uptake by the floating macrophyte Lemna minor
Authors: Cedergreen Nina , Madsen Tom Vindbæk 
Published: March 2003

Summary

Both roots and leaves of free‐floating plants can potentially take up nutrients. In this study, the ability and relative contribution of roots and fronds for N uptake by the floating macrophyte Lemna minor was investigated.
The NH 4
+
and NO
3
−
uptake kinetics of roots and fronds were measured on plants acclimated to three different NH
4NO3 concentrations.
Lemna
had the capacity to take up NH
4
+
and NO
3
− through both roots and fronds; uptake kinetics for the two tissue types were comparable on an area basis. The overall contribution of root and frond to whole‐plant uptake, estimated from measured kinetic characteristics, varied depending on plant N status (the root contribution increased from 32 to 73% for N‐satiated and N‐depleted plants, respectively).
The shift in the balance between root and frond contribution to whole‐plant uptake resulted from a 1.5–38 times greater increase in the area‐specific uptake capacity and affinity of roots relative to fronds, combined with a larger decrease in the minimum concentration for uptake ( C
min ) for roots than fronds. At the morphological level, root–frond surface area increased with declining N supply, which might be beneficial to the plants since the area return per unit biomass invested was nine times greater for roots than for fronds.