bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular phylogeny of Flaveria as deduced from the analysis of nucleotide sequences encoding the H‐protein of the glycine cleavage system
Authors: KOPRIVA S. , CHU C.‐C. , BAUWE H.
Published: April 2006

Sequence comparisons have shown that nucleotide sequences of the H‐protein, a component of the glycine cleavage system, are only moderately conserved and can be used as molecular markers for intrageneric phylogenetic studies. We have analysed the respective cDNA sequences from 12 species of Flaveria, and a more limited set of gdcsH upstream regions. These data are discussed with respect to a phylogenetic reconstruction of Flaveria, a small genus which includes species of different photo‐synthetic types, namely C3, C3‐C4, C4‐like and C4. Our analysis essentially supports an earlier hypothesis, based on morphological and eco‐geographical data, of the evolution of Flaveria (Powell 1978). This close agreement shows the usefulness of H‐protein nucleotide sequences at a low taxonomic level. Our analysis independently confirms that C4 photosynthesis has evolved two times in different lineages of Flaveria. Most remarkably, the C4 taxa of Flaveria appear as derived relative to the C3‐C4 intermediate taxa, i.e. they probably have common direct predecessors. This is the first direct evidence for a phylo‐genetically intermediate position of C3‐C4 intermediate photosynthesis. Our data also confirm the antiquity of C3 photosynthesis in Flaveria but suggest that the collection of F.pringlei used in our experiments, although clearly of C3 photosynthetic metabolism, possibly originated from hybridization with a more advanced taxon.
Interactions between K+ and NH4+: effects on ion uptake by rice roots
Authors: WANG M. Y. , SIDDIQI M.Y. , GLASS A. D. M.
Published: April 2006

Interactive effects of K+ and N (principally NH4+) on plant growth and ion uptake were investigated using hydroponically grown rice (Oryza sativa L. cv. M202) seedlings by varying the availability of NH4+ or NO3− and K+ during an 18d growth period, a 3d pretreatment period and during flux measurements. Plants grew best in media containing 100 mmol m−3 NH4+ and 200mmolm−3 K+ (N100/K200), followed by N2/K200 < N100/K2 < N2/K2. 86Rb+(K+) fluxes were increased by exposure to N during the 18 d growth period and the 3 d of pretreatment, but decreased by the presence of NH4+ during flux measurements. This inhibition was a function of prior N/K provision and the [NH4+]0 present during flux determinations. NH4+ was least inhibitory to 86Rb+(K+) influx in high‐N/low‐K plants. Pretreatments with K+ failed to stimulate NH4+ uptake, and the presence of K+ in the uptake solutions reduced NH4+ fluxes only in high‐N/low‐K plants.
Thermodynamic analysis of the physical state of water during freezing in plant tissue, based on the temperature dependence of proton spin‐spin relaxation
Authors: MILLARD M. M. , VEISZ O. B. , KRIZEK D. T. , LINE M.
Published: April 2006

Multi‐proton spin‐echo images were collected from cold‐acclimated winter wheat crowns (Triticum aestivumL.) cv. Cappelle Desprez at 400 MHz between 4 and −4 °C. Water proton relaxation by the spin‐spin (T2) mechanism from individual voxels in image slices was found to be mono‐exponential. The temperature dependence of these relaxation rates was found to obey Arrhenius or absolute rate theory expressions relating temperature, activation energies and relaxation rates, Images whose contrast is proportional to the Arrhenius activation energy (Ea), Gibb's free energy of activation (ΔG‡), and the entropy of activation (ΔS‡) for water relaxation on a voxel basis were constructed by post‐image processing. These new images exhibit contrast based on activation energies rather than rules of proton relaxation. The temperature dependence of water protonT2relaxation rates permits prediction of changes in the physical state of water in this tissue over modest temperature ranges. A simple model is proposed to predict the freezing temperature kof various tissue in wheat crowns. The averageEaand ΔH‡for water protonT2relaxation over the above temperature range in winter wheat tissue were −6.4 ± 14.8 and −8.6 ± 14.8kj mol−1, respectively. This barrier is considerably lower than theEafor proton translation in ice at 0°C, which is reported to be between 46.0 and 56.5 kj mol−1
Phloem‐specific expression of pyrophosphatase inhibits long distance transport of carbohydrates and amino acids in tobacco plants
Authors: GEIGENBERGER P. , LERCHI J. , STITT M. , SONNEWALD U.
Published: April 2006

As reported in a previous paper [Lerchl et al. (1995) Plant Cell, 7, 259–270], expression of Escherichia coli inorganic pyrophosphatase in the cytosol under the control of the phloem‐specific rolC promoter from, Agobacterium rhizogenes results in decreased growth of transgenic tobacco plants. In this paper we investigate the effect of the phloem‐specific expression of pyrophosphatase on phloem metabolism, and on plant growth and allocation. A small decrease in the hexose phosphate/UDP‐glucose ratio, the ATP/ADP ratio and the respiration rate in the midribs of the transformants provides evidence Hint mobilization of sucrose via pyrophosphate‐dependent reactions is necessary for phloem energy metabolism. The source leaves of the transformants had higher levels of carbohydrates and amino acids and a much higher glutamine/glutamate ratio than the wild type, showing that export was inhibited and that the growth inhibition was not due to a lack of photoas‐similates or organic nitrogen in the leaves. The accumulation of photoassimilates was paralleled by a decrease in photosynthesis, chlorophyll content and ribulose bisphosphate carboxylase/oxygenase (Rubisco) activity, a small increase in hexose phosphates and triose phosphates and a decrease in glycerate 3‐phosphate in the source leaves. There was a decrease of soluble sugars and amino acids in sink leaves of the transformants. In sink leaves amino acids decreased more than carbohydrates and a decrease in the glutamine/ glutamate ratio was observed. This was accompanied by a large decrease of nitrate. Sugars and amino acids were also reduced in the root tips of the transformants. The carbohydrate /amino acid ratio decreased 5‐fold in the root tips, indicating a particularly smile shortage of carbohydrates. Relatively high levels of sugars and amino acids in the basal regions of the root and the increase in sugars in the midrib indicate that there is also increased leakage of assimilates out of the phloem during long‐distance transport. Metabolism is required to maintain phloem function along the transport route, as well as for the initial step of loading. The transformants showed decreased stem and root growth. The growth inhibition was largest in conditions allowing rapid growth of the wild type (high light and nitrogen supply).
Physiological and biochemical changes related to methyl jasmonate‐induced chilling tolerance of rice (Oryza sativa L.) seedlings
Authors: LEE T.‐M. , LUR H.‐S. , LIN Y.‐H. , CHU C.
Published: April 2006

Physiological and biochemical changes related to methyl jasmonate (MeJA)‐induced chilling tolerance of rice (Oryza sativa L. cv. Taichung Native 1) seedlings were investigated. Treatment of whole plants with 10 mmol m−3 MeJA for 48 h before chilling (5 °C) was optimal for the induction of chilling tolerance. MeJA greatly improved the survival ratio of chilled seedlings and ameliorated chilling injury such as demolition of membrane structure (estimated by electrolyte leakage). MeJA also prevented water loss in chilled seedlings by reducing the opening of stomata and decreasing the root bleeding rate. Putrescine and spermine levels in shoots increased but spermidine levels decreased on exposure to MeJA. In roots, putrescine levels also increased and spermidine levels increased transiently on exposure to MeJA. Activities of arginine decarboxylase (ADC; EC 4.1.1.19) and S‐adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) in both shoots and roots increased on exposure to MeJA, while the activity of ornithine decarboxylase (ODC; EC 4.1.1.17) remained unchanged. The MeJA‐induced putrescine increase was inhibited by 50 mmol m−3α‐difluoromethylarginine (DFMA), an irreversible inhibitor of ADC, but not by 50 mmol m−3α‐difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. The effect of MeJA on the induction of chilling tolerance was also reduced by 50 mmol m−3 DFMA. The effects of DFMA were partly prevented by 1 mol m−3 putrescine. This indicates that putrescine accumulation is required for the induction of chilling tolerance of rice seedlings by MeJA.
Effects of light regime on δ13C, photosynthesis and yield of field‐grown banana (Musa sp., Musaceae)*
Authors: ISRAELI Y. , SCHWARTZ A. , PLAUT Z. , YAKIR D.
Published: April 2006

Banana plants (Musa sp., Musaceae) were grown for 2 years in the field in 12×20m plots under irradiance levels incident upon the canopy of 100, 81, 62 and 32% of sunlight. Time‐integrated parameters such as leaf δ13C, yield and leaf mass to area ratio were linearly correlated with irradiance level (R2>0.9). In contrast, midday CO2 assimilation and transpiration efficiency (A/g) decreased significantly and substomatal CO2 concentrations (cst) increased significantly only at the lowest irradiance levels (below 81% irradiance). Diurnal gas exchange measurements indicated that the linear response of the long‐term parameters may be associated with the significant variations in photosynthetic activity among the irradiance treatments observed only in the early morning hours. The linear fit between yield and irradiance level (per cent of control) had a slope of 0.82 (with apparently constant yield to biomass ratio). These results directly demonstrate the significance of variations in incident light, such as may be associated with increasing cloudiness, on productivity of tropical plants such as the banana. The importance of using time‐integrated indicators in general, and the reliability of using 13C discrimination in particular, in evaluating the responses of plants to changes in incident irradiance is demonstrated.
Glucose feeding of intact wheat plants represses the expression of a number of Calvin cycle genes
Authors: JONES P. G. , LLOYD J. C. , RAINES C. A.
Published: April 2006

The photosynthetic capacity and Rubisco levels of primary wheat leaves were reduced significantly in plants grown on media supplemented with 1 % glucose. Neither the chlorophyll content nor the growth rate of the primary leaf was affected by this treatment. In glucose‐fed plants a decrease in levels of mRNA encoding several Calvin cycle enzymes (fructose 1,6‐bisphosphatase, sedoheptulose 1,7‐bisphosphatase, phosphoglycerate kinase and Rubisco Small Subunit) was found to correspond to an increase in the internal levels of glucose. In control plants endogenous levels of glucose and sucrose were measured in leaf sections from the base to the tip of the primary leaf, which revealed a gradient of each of these sugars within the leaf, with the highest levels at the tip. Conversely, Calvin cycle transcripts were seen to decrease in the oldest tip sections. In glucose‐fed plants, the endogenous glucose levels were increased throughout the leaf but Calvin cycle RNA levels were most markedly reduced in the mid‐leaf section. These data indicate that the changing metabolic status of the cells from the base to the tip of the primary wheat leaf may play a role in the regulation of Calvin cycle gene expression during normal leaf development.
Exchange diffusion of alkali ions through the apoplast of the potato (Soianum tuberosum L.) storage parenchyma
Authors: MICHAEL W. , EHWALD R.
Published: April 2006

Interdiffusion coefficients of K and Na for tangential transport through cell walls were found to be independent of ion strength and only moderately (c. 50%) lower than values known for diffusion in water. Although at low salt concentrations alkali ion exchange diffusion on the cell wall pathway is facilitated by accumulation of diffusing species in the Donnan space, at all concentrations the resistance of the whole tissue for apoplastic cation exchange diffusion remained significantly higher than that of unstirred liquid of equal thickness, as the area fraction of the cell wall pathway in the parenchyma is small.
Influx and efflux of inorganic carbon in Synechococcus UTEX625
Authors: SALON C. , MIR N. A. , CANVIN D. T.
Published: April 2006

The CO2 and HCO3− fluxes in air‐grown cells of Synechococcus UTEX 625 al pH 8‐0 were measured during dark to light and light to dark transitions using a mass spectrometer and sampling of the reaction medium. The kinetic parameters for initial uptake of CO2 and HCO3− were determined during the initial period of illumination. The development of the internal Ci pool was followed up to steady‐state photosynthesis, which occurred when the size of the internal inorganic carbon pool remained apparently constant for a limited period. The experimental procedure confirmed that only CO2 transport occurred with 100mmolm−3 Na+ and that both CO2 and HCO−3 transport occurred with 25molm−3 Na+. The K1/2 values of initial CO2 and HCO3 uptake were 0.7 and 17.2 mmolm−3respectively and agreed closely with the K1/2 values of net CO2 and HCO3− transport during steady‐state photosynthesis, which were 0.66 and 17.1 mmolm−3 respectively. Maximum rates of CO2and HCO3− transport were 423 and 219mmolh−1 g−1 Chl. Maximum CO2 efflux observed upon darkening was 118mmolh−1 g−1 Chl. A permeability coefficient of the cell for CO2 of 3 × 10−8 m s−1 was determined from the dark CO2 efflux assuming an internal pH of 7.2 in the dark. Following the initial CO2 uptake in the light, the extracellular [CO2] steadily declined when only CO2 transport was allowed, but an increase in the extracellular [CO2] when HCO3− transport was allowed to proceed suggested that an enhanced CO2 efflux occurred as a result of the larger size of the intracellular Ci pool.
HCO3− and CO2 leakage from Synechococcus UTEX 625
Authors: SALON C. , MIR N. A. , CANVIN D. T.
Published: April 2006

The leakage of various inorganic carbon species from air‐grown cells of Synechococcus UTEX 625 was investigated after a light to dark transition or during a light period using a mass spectrometer under a wide variety of experimental conditions. Total inorganic carbon efflux and CO2 efflux during the initial period of darkness were measured with or without carbonic anhydrase in the reaction medium respectively. The HCO3− efflux after a light to dark transition was estimated by difference. Carbon dioxide efflux in the light was measured by inhibiting CO2 transport with either Na2S or COS3 or quenching the 13C inorganic carbon transport by the addition of 12C inorganic carbon in excess. In cells in which CO2 fixation was inhibited, when only the HCO3− transport system was fully operative, CO2 effluxed continuously during the light period at a rate equal to about 25% of that in darkness. When only the CO2 transport system was operative, HCO3− effluxed during the light period. The difference between the light and dark efflux rates was consistent with a 0.6 unit decrease in the intracellular pH upon darkening the cells. The permeabilities of the cell for CO2 (2.94 ± 0.14 ± 10−8ms−1; mean ± SE, n=137) and HCO3− (1.4–1.7 ± 10−9 ms−1) were calculated.
The involvement of the transpirational bypass flow in sodium uptake by high‐ and low‐sodium‐transporting lines of rice developed through intravarietal selection
Authors: YADAV R. , FLOWERS T. J. , YEO A. R.
Published: April 2006

We report the characterization of high‐ and low‐sodium‐transporting lines developed by intravarietal selection within a cultivar, IR36, of rice (Oryza sativa L.). The purpose was to investigate the mechanistic basis of sodium uptake in material in which differences in salt uptake could be isolated from the many other morphological and physiological characteristics that affect the phenotypic expression of salt tolerance. The lines differed in mean sodium transport by a factor of 2. They differed in vigour and water use efficiency, which are characters that modify the effects of salt transport, by only 12% or 13%. The lines did not differ significantly in other physiological traits that are components of salt resistance: compartmentalization at the leaf and cellular levels. There was a strong correlation between the transport of sodium and a tracer for apoplastic pathways (trisodium, 3‐hydroxy‐5,8,10‐pyrene trisulphonic acid, PTS) in both lines. The regression coefficient for sodium transport on PTS transport was the same in both lines. The individual variation in PTS transport was similar to that in sodium transport, and the variation in the transport of both was very much greater than the variation in any other character studied. The high‐sodium‐transporting line took up proportionately more PTS than the low‐sodium‐transporting line. It is concluded that the transpirational bypass flow is of major importance in sodium uptake by rice and that selection for differences in sodium transport has been brought about by selection for heritable differences in the bypass flow.
The interpretation of leaf‐drying curves
Authors: CAPE J. N. , PERCY K. E.
Published: April 2006

A 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

The 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

We 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

In 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

The 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

The 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

Six 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

The 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

Ion 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

Glutamine 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

In 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

Concurrent 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

We 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

We 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

We 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

New 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.
Carbon isotopic composition and oxygen isotopic enrichment in phloem and total leaf organic matter of European beech (Fagus sylvatica L.) along a climate gradient
Authors: KEITEL CLAUDIA , MATZARAKIS ANDREAS , RENNENBERG HEINZ , GESSLER ARTHUR
Published: April 2006

This study investigated the influence of climate on the carbon isotopic composition (δ13C) and oxygen isotopic enrichment (Δ18O) above the source water of different organic matter pools in European beech. In July and September 2002, δ13C and Δ18O were determined in phloem carbohydrates and in bulk foliage of adult beech trees along a transect from central Germany to southern France, where beech reaches its southernmost distributional limit. The data were related to meteorological and physiological parameters. The climate along the transect stretches from temperate [subcontinental (SC)] to submediterranean (SM). Both δ13Cleaf and Δ18Oleaf were representative of site‐specific long‐term environmental conditions. δ13C of leaves collected in September was indicative of stomatal conductance, vapour pressure deficit (VPD) and radiation availability of the current growing season. Δ18O was mainly correlated to mean growing season relative humidity (RH) and VPD. In contrast to the leaves, δ13Cphloem varied considerably between July and September and was well correlated with canopy stomatal conductance (Gs) in a 2 d integral prior to phloem sampling. The relationship between δ13C and Δ18O in both leaves and phloem sap points, however, to a combined influence of stomatal conductance and photosynthetic capacity on the variation of δ13C along the transect. Δ18Ophloem could be described by applying a model that included 18O fractionation associated with water exchange between the leaf and the atmosphere and with the production of organic matter. Hence, isotope signatures can be used as effective tools to assess the water balance of beech, and thus, help predict the effects of climatic change on one of the ecologically and economically most important tree species in Central Europe.
Translocation of Phosphorus‐32 in Sporophores of Collybia velutipes
Authors: Littlefield Larry J.
Published: April 2006

Phosphorus‐32 was absorbed by the mycelium of Collybia velutipes and translocated to the pilei of intact sporophores within 1.5 hours. In the stipes upward translocation occurred first in the peripheral hyphac followed by movement of the isotoipe into the central hyphac. After 3.0 hours hyphae in the two regions were about equally labelled with the isotope. Except for very minor differences hyphal was the same in the peripheral and central portions of the stipe.
Adjustment to Light and Dark Rates of Coccolith Formation
Authors: Paasche E.
Published: April 2006

Coccolith formation in Coccolithus huxleyi was investigated in a semiquantitative manner by microscopic enumeration of coccolith‐carrying cells appearing, after varying periods in normal growth medium, following an initial removal of all coccoliths by treatment with a decalcifying medium. Coccoliths were formed both in the light and in the dark, but the rate of coccolith formation was very much greater in the light.

Time‐course experiments on the uptake of carbon‐14 in coccoliths demonstrated that after a period in darkness, the cells required half an hour of illumination in order to adjust to the light rate of coccolith formation. Coccoliths were produced at a maximum rate only as long as the illumination lasted, although about one hour in the dark was needed before the transition back to the original dark rate was complete.
Transpiration and Calcium Deposition by Unifoliate Leaves of Phaseolus vulgaris Differing in Maturity
Authors: Koontz H. V. , Foote Roberta E.
Published: April 2006

Unifoliate leaves were individually enclosed in clear, plastic chambers for the 24 hour treatment periods and then sacrificed for Ca analysis. Two transpiration rates were obtained by passing dry air through the chambers tising flow rates of 160 and 260 cm3/min. A third rate was obtained by a combination of shade and the lower air flow rate.

Neither the transpiration rate nor solution‐Ca concentration (0.5mM and 2.5 mM of 0.1, and 0.5 strength Hoagland solution) altered the amount of Ca deposited in the unifoliate leaves of 22 day old bean plants (Phaseolus vulgaris). The transpiration rate per unit area of leaf remained constant for all ages studied (1l–20 days) and was 1.8, 2.7, 3.6 g H2O per dm2 day for the three different imposed conditions.

A definite pattern of Ca deposition occurred. With all the transpiration rates there was a maximum rate of calcium deposition at 13 days of growth and a gradual decrease thereafter. When the Ca concentration of the nutrient solution was 20 μg/ml the daily Ca deposition in terms of water transpired by the unifoliate leaves exceeded this amount, except for the oldest leaf tested, and, the maximum Ca to water ratios were 250, 320, and 430 (μg Ca/g) in order of decreasing transpiration rates.

The uptake of Ca against a concentration gradient and approximately the same total uptake regardless of transpiration rates and solution concentrations used, firmly suggest that Ca secretion into root‐xylem elements from a surrounding low level Ca solution requires energy expenditure by the plant.

A possible explanation was proposed for the decreased rate of Ca deposition by the unifoliate leaves subsequent to the 13th day.
Calcium Uptake by Potato Tuber Mitochondria
Authors: Grunwald C.
Published: April 2006

An attempt was made to isolate from potato tuber mitochondria the reported calcium‐45 complex. Mitochondria fractionation results showed that the lipids were not involved in the calcium‐45 complex formation. Using hot water as an extracting solvent it was found that two calcium‐45 complexes occurred in the mitochondria fraction. One of the complexes was readily removable while the other complex was much less readily extractable with hot water. The readily removable calcinm‐45 complex was identified as calcium phosphate and the less readily extractable complex seemed to be directly related to mitochondrial RNA liberation, however, it was impossible to isolate a calcium‐45 ribonucleic acid complex. The extraction of the slowly removable calcium‐45 complex was not a simple liberation of the complex but rather a breakdown which was irreversible and could be inhibited partially by sodium arsenate.

A possible explanation of these data is that the TCA soluble fraction represents the total calcium45 uptake by the mitochondria, that is, the calcium‐45 that has been accumulated plus that which is in the “calcium‐carrier complex”. It is suggested that the easily extractable hot water fraction is the accumulated calicum‐45 while the less readily extractable fraction is the “calcium‐carrier complex”.