bluuebunny/crossref_metadata_2025_split huggingface dataset:
The interpretation of leaf‐drying curves
Authors: CAPE J. N. , PERCY K. E. 
Published: April 2006

ABSTRACTA theoretical expression for the rate of water loss through the surface of excised leaves has been derived so that curves fitted to experimental data can be used to infer physical properties of the leaves such as the solute concentration and the conductance for water vapour loss. The use of the equations is illustrated by reference to data from an experiment in which red spruce (Picea rubens Sarg.) and Norway spruce (P. abies(L.) Karst.) seedlings were grown under five different regimes: outdoors (±50% shade), in a greenhouse (±50% shade) and in controlled‐environment chambers.
Differential responses of root uptake kinetics of NH4+ and NO3− to enriched atmospheric CO2 concentration in field‐grown loblolly pine
Authors: BASSIRIRAD H. , THOMAS R. B. , REYNOLDS J. F. , STRAIN B. R. 
Published: April 2006

ABSTRACTThe nitrogen requirement of plants is predominantly supplied by NH4+ and/or NO3− from the soil solution, but the energetic cost of uptake and assimilation is generally higher for NO3− than for NH4+. We found that CO2 enrichment of the atmosphere enhanced the root uptake capacity for NO3−, but not for NH4+, in field‐grown loblolly pine saplings. Increased preference for NO3− at the elevated CO2 concentration was accompanied by increased carbohydrate levels in roots. The results have important implications for the potential consequences of global climate change on plant‐and ecosystem‐level processes in many temperate forest ecosystems.
Effects of drought on nutrient and ABA transport in Ricinus communis
Authors: SCHURR U. , SCHULZE E.‐D. 
Published: April 2006

ABSTRACTWe studied the effects of variations of water flux through the plant, of diurnal variation of water flux, and of variation of vapour pressure deficit at the leaf on compensation pressure in the Passioura‐type pressure chamber, the composition of the xylem sap and leaf conductance in Ricinus communis. The diurnal pattern of compensation pressure showed stress relaxation during the night hours, while stress increased during the day, when water limitation increased. Thus compensation pressure was a good measure of the momentary water status of the root throughout the day and during drought. The bulk soil water content at which predawn compensation pressure and abscisic acid concentration in the xylem sap increased and leaf conductance decreased, was high when the water usage of the plant was high. For all xylem sap constituents analysed, variations in concentrations during the day were larger than changes in mean concentrations with drought. Mean concentrations of phosphate and the pH of the xylem sap declined with drought, while nitrate concentration remained constant. When the measurement leaf was exposed to a different VPD from the rest of the plant, leaf conductance declined by 400mmol m−2 s−1 when compensation pressure increased by 1 MPa in all treatments. The compensation pressure needed to keep the shoot turgid, leaf conductance and the abscisic acid concentration in the xylem were linearly related. This was also the case when the highly dynamic development of stress was taken into account.
Isolation, characterization and expression of a cDNA coding for a jasmonate‐inducible protein of 37 kDa in barley leaves
Authors: LEOPOLD J. , HAUSE B. , LEHMANN J. , GRANER A. , PARTHIER B. , WASTERNACK C. 
Published: April 2006

ABSTRACTIn barley leaves, there is a dramatic alteration of gene expression upon treatment with jasmonates leading to the accumulation of newly formed proteins, designated as jasmonate‐inducible proteins (JIPs). In the present study, a new jasmonate‐inducible cDNA, designated pHvJS37, has been isolated by differential screening of a γgt10 cDNA library constructed from mRNA of jasmonate‐treated barley leaf segments. The open reading frame (ORF) encodes a 39‐9 kDa polypeptide which cross‐reacts with antibodies raised against the in vivo JIP‐37. The hydropathic plot suggests that the protein is mainly hydrophilic, containing two hydrophilic domains near the C‐terminus. Database searches did not show any sequence homology of pHv.JS37 to known sequences. Southern analysis revealed at least two genes coding for JIP‐37 which map to the distal portion of the long arm of chromosome 3 and are closely related to genes coding for JIP‐23. The expression pattern of the JIP‐37 genes over time shows differential responses to jasmonate, abscisic acid (ABA), osmotic stress (such as sorbitol treatment) and desiccation stress. No expression was found under salt stress. From experiments using an inhibitor and intermediates of jasmonate synthesis such as α‐linolenic acid and 12‐oxophytodienoic acid, we hypothesize that there is a stress‐induced lipid‐based signalling pathway in which an endogenous rise of jasmonate switches on JIP‐37 gene expression. Using immunocytochemical techniques, JIP‐37 was found to be simultaneously located in the nucleus, the cytoplasm and the vacuoles.
Reassessing the nitrogen relations of Arctic plants: a mini‐review
Authors: ATKIN O. K. 
Published: April 2006

ABSTRACTThe Arctic is often assumed to be an NH4+‐dominated ecosystem. This review assesses the validity of this assumption. It also addresses the question of whether Arctic plant growth is limited by the ability to use the forms of nitrogen that are available. The review demonstrates that several sources of soil nitrogen are available to Arctic plants, including soluble organic nitrogen (e.g. glycine, aspartic acid and glutamic acid), NH4+ and NO−3. In mesic Arctic soils, soluble organic nitrogen is potentially more important than either NH+4 or NO−3. Many Arctic species are capable of taking up soluble organic nitrogen (either directly and/or in association with ectomycorrhizae), with the greatest potential for soluble organic nitrogen uptake being exhibited by deciduous species. The ability to take up soluble organic nitrogen may enable some Arctic plants to avoid nitrogen limitations imposed by the slow rate of organic matter decomposition. NO−3 is also present in many Arctic soils, especially calcareous soils and soils near flowing water, animal burrows and bird cliffs. Arctic species characteristic of mesic and xeric habitats are capable of taking up and assimilating NO−3. Even when present in lower concentrations in soils than NH+4, NO−3 is still an important source of nitrogen for some Arctic plants. Arctic‐plants therefore have a variety of nitrogen sources available to them, and are capable of using those nitrogen sources. Taken together, these findings demonstrate that the Arctic is not an NH+4dominated ecosystem. Symbiotic fixation of atmospheric N2 does not appear to be an important source of nitrogen for Arctic plants. The reliance of Arctic plants on internal recycling of nitrogen substantially reduces their dependence on soil nitrogen uptake (this is particularly the case for slow‐growing evergreens). Despite the high level of internal nitrogen recycling, Arctic plant growth remains limited by the low levels of available soil nitrogen. However, Arctic plant growth is not limited by an inability to utilize any of the available forms of nitrogen. The potential effects of climatic warming on nitrogen availability and use are discussed. The question of whether the Arctic ecosystem is uniquely different from temperate nitrogen‐deficient ecosystems is also assessed.
Variations in stomatal density and index: implications for palaeoclimatic reconstructions
Authors: Poole I. , Weyers J. D. B. , Lawson T. , Raven J. A. 
Published: April 2006

ABSTRACTThe variation in stomatal characters in leaves from one Alnus glutinosa (L.) Gaertn. tree is analysed. Measurements were taken from over 70 sites on the abaxial surfaces of representative ‘sun’ and ‘shade’ leaves having the same insertion point. The mean values of stomatal density and index in the shade leaf were significantly lower (71 and 93%, respectively) than those for the sun leaf. Within leaves, up to 2.5‐fold differences in stomatal density values were observed. Contour maps derived from the data reveal non‐random trends over the leaf surface. Correlations between stomatal density, epidermal cell density and stomatal index indicate that the variation in stomatal density within leaves arose primarily from local differences in stomatal differentiation, rather than from local differences in leaf expansion. This research demonstrates that a high level of variation in stomatal characters occurs both within and between leaves. We conclude that a well‐defined sampling strategy should be used when estimating stomatal characters for (tree) leaves. Furthermore, the leaf's insertion point and situation within the tree crown should be taken into account. We discuss the implications of these findings for palaeoclimatic interpretations and emphasize the need for great caution when drawing conclusions based solely on stomatal characters.
Variable patterns of antioxidant protection but similar ethene emission differences in several ozone‐sensitive and ozone‐tolerant plant selections
Authors: Wellburn F. A. M. , Wellburn A. R. 
Published: April 2006

ABSTRACTSix pairs of O3‐sensitive and O3‐tolerant cultivars, clones or populations of different plants (tobacco, plantain, clover, radish, poplar and loblolly pine) were taken through identical but short episodic exposures to O3 in a controlled‐environment fumigation system. Emissions of ethene and concentrations of polyamines, total phenols and ascorbate as well as levels of reduced glutathione and ascorbate in fumigated and clean air controls were determined in these various cultivars, clones and populations. A large number of significant differences were detected between the various sensitive and tolerant pairs, but it is clear that different sequences of response involving these parameters occur in these various plant pairs to account for their individual O3 sensitivity or tolerance. Some O3‐tolerant plants have increased polyamines, others total phenols and some appear to be able to form reduced ascorbate and glutathione more rapidly. In the case of ethene emissions, however, all O3‐sensitive selections produce more ethene when fumigated while O3‐tolerant ones either reduce their rates of emissions below those of clean air‐grown controls or at least keep them at the same level.
Effects of temperature and elevated CO2on cell division in shoot meristems: differential responses of two natural populations ofDactylis glomerataL.
Authors: KINSMAN E. A. , LEWIS C. , DAVIES M. S. , YOUNG J. E. , FRANCIS D. , THOMAS I. D. , CHORLTON K. H. , OUGHAM H. J. 
Published: April 2006

ABSTRACTThe aim was to establish whether temperature and/or elevated [CO2] (‐700 μmol mol−1) affects the cell doubling time (cdt) in the different zones of the shoot apex of two natural populations ofDactylis glomerataoriginating in Portugal (38° S3′ N) and in Sweden (63° 09′ N).In the Portuguese population at ambient [CO2], only the pith rib meristem (PRM) exhibited a significant shortening of cdts from 10 to 30 °C. Elevated [CO2] resulted in a significant shortening of cdt, particularly in the PRM where cdt was reduced 4‐8‐ and 6‐1‐fold at 10 and 20 °C, respectively, but only 2‐fold at 30 °C. In the Swedish population at ambient [CO2], there were no consistent temperature‐dependent alterations to cdt and this population was less responsive to elevated [CO2] than the Portuguese population. Nevertheless, elevated [CO2] resulted in a significant shortening of the cdt for some of the zones; the maximum reduction occurred in the PRM at 30 °C.We concluded that in the shoot apex of the Portuguese population, and most notably in the PRM, 10 and 20 °C were non‐optimal temperatures for cell division, whilst the Swedish population was relatively buffered against temperature change. Elevated [CO2] resulted in substantially greater reductions in cdts in the shoot meristem of the Portuguese population than in that of the Swedish population.
SO2‐dependent cation competition and compartmentalization in Norway spruce needles
Authors: SLOVIK S. , HÜVE K. , KINDERMANN G. , KAISER W. M. 
Published: April 2006

ABSTRACTIon contents in needles from Norway spruce trees [Picea abies (L.) Karst.] growing in Würzburg and in the SO2‐polluted Erzgebirge mountains were analysed to quantify cations which accumulate together with sulphate. In Würzburg there was a positive correlation of potassium (0.680 ± 0.300 Eq Eq−1 SO4−2), magnesium (0.415 ± 0.111 Eq Eq−1 SO4−2) and zinc (0.059 ± 0.006 Eq Eq−1 SO42−). In the Erzgebirge, potassium was also the stoichiometrically most important cation (0–887 ± 0–180 Eq K+ Eq−1 SO42−). All other correlations examined were weak or statistically non‐significant. At both sites the calcium content of spruce needles did not depend on the sulphate content. The lack of a role for Ca2+ in neutralizing sulphate is a consequence of the presence of free oxalic acid in needles. Soluble oxalic acid precipitates Ca2+, which thereby becomes unavailable as a counterion for SO42−. The activity coefficients of Ca2+ and oxalate2−, and the solubility product of Ca‐oxalate, were determined from in vivo data. It is concluded that the chronic accumulation of atmospheric sulphate in spruce needle vacuoles depletes available potassium and thereby strongly interferes with spruce growth and canopy turnover. This leads to impaired spruce vitality, even at sites where acute SO2 disease symptoms are absent.
Glutamine synthetase polypeptides in the roots of 55 legume species in relation to their climatic origin and the partitioning of nitrate assimilation
Authors: WOODALL J. , FORDE B. G. 
Published: April 2006

ABSTRACTGlutamine synthetase (GS) exists as two main isoforms in plants, a cytosolic form (GSI) and a chloroplast or plastidie form (GS2). Fifty‐five species of legume, representing a phylogenetically diverse group of tropical and temperate species, were screened by western blotting for the presence of GS2 in their roots. A remarkably strong correlation was found between the climatic origin of the species and the presence or absence of a GS2‐like polypeptide in the root. Root GS2 was found in all 31 temperate species examined (30 papilionoids, one caesalpinoid), but was not detected in any of the 17 tropical papilionoid species. It was also absent in the roots of four out of seven tropical non‐papil‐ionoid species. The ‘in vivo’ NR activities of roots, stems and leaves of 46 of the legume species were analysed to establish their major site of nitrate reduction, and the ratio of nitrate: reduced N in the xylem sap was determined for some species, but no clear correlation between possession of a root GS2 and a preference for root nitrate assimilation was found. We discuss the possibility that expression of GS2 in the root was part of a more extensive physiological adaptation to root nitrate assimilation that evolved in temperate species to suit the alkaline, nitrate rich soils found in the centres of origin in temperate latitudes.
Companion cell‐specific inhibition of the potato sucrose transporter SUT1
Authors: KÜHN C. , QUICK W. P. , SCHULZ A. , RIESMEIER J. W. , SONNEWALD U. , FROMMER W. B. 
Published: April 2006

ABSTRACTIn many plants, translocation of sucrose from mesnsophyll to phloem for long‐distance transport is carrier‐mediated. The sucrose H+‐symporter gene SUT1 from potato is expressed at high levels in the phloem of mature, exporting leaves and at lower levels in other organs. Inhibition of SUT1 by expression of an antisense gene in companion cells under control of the rolC promoter leads to accumulation of high amounts of soluble and insoluble carbohydrates in leaves and inhibition of photosynthesis. The distribution of in situ localized starch does not correspond with areas of reduced photosynthesis as shown by fluorescence imaging. Dissection of antisense effects on sink and source organs by reciprocal grafts shows that inhibition of transporter gene expression in leaves is sufficient to produce chlorosis in leaves and reduced tuber yield. In contrast to the arrest of plasmodesmal development found in plants that express yeast invertase in the apoplast, in mature leaves of sucrose transporter antisense plants plasmodesmata are branched and have median cavities. These data strongly support an apoplastic mode of phloem loading in potato, in which the sucrose transporter located at the plasma membrane of the sieve element/companion cell complex represents the primary route for sugar uptake into the long‐distance translocation pathway.
Comparison of sap flow, cavitation and water status of Quercus petraea and Quercus cerris trees with special reference to computer tomography
Authors: TOGNETTI R. , RASCHI A. , BÉRES C. , FENYVESI A. , RIDDER H.‐W. 
Published: April 2006

ABSTRACTConcurrent measurements of sap velocity (heat pulse) and ultrasound acoustic emission were performed on the trunks of mature Turkey oak (Quercus cerris) and sessile oak (Quercus petraea) trees. Plant water status was assessed by measuring leaf water potential, leaf conductance and transpiration. Wood density was estimated non‐destructively on the trunk section of the plants by mobile computer tomography, which measures the attenuation of a collimated beam of radiation traversing the trunk in several directions, as the device rotates around the tree. Absorption is proportional to the density of the wood. As wood density is strictly correlated to water content, this non‐invasive method allows the water content in the trunk section to be evaluated as well as mapped. Leaf water potential declined each morning until a minimum was reached at midday and recovered in the afternoon, lagging behind changes in transpiration rate. Good correspondence was found between the patterns of sap velocity and cavitation rate. A close correlation was demonstrated between wood density, water content and sap velocity. Sap now was always higher in Turkey oak than in sessile oak. Trunk signatures by computer tomography appeared to differentiate the two oak species, with the Turkey oak stem clearly more hydrated than the sessile oak; water storage reservoirs could play an important role in tree survival during extended periods of low soil water availability and in the relative distribution of tree species, especially in the context of global climate change. Late‐wood conducting elements of oak species seem to play a significant role in water transport. The mobile computer tomograph was confirmed as a peerless tool for investigating stem water relations. Diurnal variations in the measured parameters under natural drought conditions and the differences between the two oak species are discussed.
Radial patterns of xylem sap flow in non‐, diffuse‐ and ring‐porous tree species
Authors: PHILLIPS N. , OREN R. , ZIMMERMANN R. 
Published: April 2006

ABSTRACTWe investigated radial patterns of sap flux density and wood properties in the sapwood of young loblolly pine (Finns taeda L.), mature white oak (Quercus alba L.) and sweetgum (Liquidambar styraciflua L.), which represent three major classes of wood anatomy: non‐porous (coniferous), ring‐porous and diffuse‐porous. Radial measurements of xylem sap flux density were made in sections of xylem extending to 20 mm and 20–40 mm from the cambium. These measurements were compared with measurements of the relative water content (Rs) and sapwood specific gravity (ρr) of corresponding radial sections. In both hardwood species, sap flow differences were rarely significant between the two depth intervals. In pine, a 59% reduction in daily sap flux density from outer to inner sapwood was found. This could not be accounted for by a 3% drop in Rs; rather, an accompanying 9% reduction in ρr indicated a transition between the depth intervals from mature to juvenile sapwood, and is the probable cause of the lower flux rate in the inner xylem of pine.
Is wall‐bound calcium redistributed during the gravireaction of stems and coleoptiles?
Authors: BAGSHAW S. L. , CLELAND R. E. 
Published: April 2006

ABSTRACTWe have tested the hypothesis that wall‐bound calcium is redistributed from the lower to the upper sides of horizontal stems and coleoptiles during the reaction phase of gravicurvature. We used atomic absorption spectrometry to measure wall‐bound calcium in the epidermal and internal layers of sunflower (Helianthus annum L.) hypocotyls and pea (Pisum sativum L.) epicotyls, and total calcium in maize (Zea mays L.) coleoptiles at the time of maximal gravireaction. In every case, we found that there was no measurable redistribution of wall‐bound calcium either from the lower to the upper sides, or between epidermal and inner tissues in response to the gravistimulus. These results indicate that a redistribution of wall‐bound calcium does not play a role during the gravireaction of stems and coleoptiles.
Relationship between stem CO2 efflux, stem sap velocity and xylem CO2 concentration in young loblolly pine trees
Authors: MAIER CHRIS A. , CLINTON BARTON D. 
Published: April 2006

ABSTRACTWe measured diel patterns of stem surface CO2 efflux (Es, µmol m−2 s−1), sap velocity (vs, mm s−1) and xylem CO2 concetration ([CO2]) (Xs, %) in 8‐year‐old loblolly pine trees during the spring to determine how vs and Xs influence Es. All trees showed a strong diel hysteresis between Es and stem temperature, where at a given temperature, Es was lower during the day than at night. Diel variations in temperature‐independent Es were correlated with vs (R2 = 0.54), such that at maximum vs, Es was reduced between 18 and 40%. However, this correlation may not represent a cause‐and‐effect relationship. In a subset of trees, vs was artificially reduced by progressively removing the tree canopy. Reducing vs to near zero had no effect on Es and did not change the diel hysteretic response to temperature. Diel Xs tended to decrease with vs and increase with Es, however, in defoliated trees, large increases in Xs, when vs ≈ 0, had no effect on Es. We conclude that at this time of the year, Es is driven primarily by respiration of cambium and phloem tissues and that sap flow and xylem transport of CO2 had no direct influence on Es.
Agravitropic mutants of the moss Ceratodon purpureus do not complement mutants having a reversed gravitropic response
Authors: COVE DAVID J. , QUATRANO RALPH S. 
Published: April 2006

ABSTRACTNew mutants of the moss Ceratodon purpureus have been isolated, which showed abnormal gravitropic responses. The apical cells of protonemal filaments of wild‐type strains respond to gravity by growing upwards and are well aligned to the gravity vector. This response only occurs in darkness. Mutants show a range of phenotypes. Some are insensitive to gravity, showing symmetrical growth, while others align to the gravity vector but orient growth downwards. A further class grows in darkness as though it were in light, showing insensitivity to gravity and continued chlorophyll synthesis. Somatic hybrids between mutants and wild‐type strains and between pairs of mutants have been selected using transgenic antibiotic resistance as selective markers. Hybrids between wild‐type strains and all of the mutants have a wild‐type phenotype, and so all mutants therefore have recessive phenotypes. Mutants comprise three complementation groups. One group has a single member, while another has three members. The third has at least 16 members and shows a complex pattern of complementation consistent with a single gene product functioning in both orientation and alignment to gravity, as well as contributing more than one subunit to the mature product.