bluuebunny/crossref_metadata_2025_split huggingface dataset:
Expression of XET‐related genes and its relation to elongation in leaves of barley (Hordeum vulgare L.)
Authors: SCHÜNMANN P. H. D. , SMITH R. C. , LÅNG V. , MATTHEWS P. R. , CHANDLER P. M. 
Published: November 2003

ABSTRACTFive cDNA clones were isolated from barley (Hordeum vulgare L.) that encoded mRNAs related to xyloglucan endotransglycosylase (XET). One of the clones encoded a protein with XET activity in vitro. Sequence comparisons revealed five families of XET‐related sequences, one of which (containing two of the barley genes) was novel. Hybridization studies using clone‐specific probes indicated that the corresponding genes were represented once, or possibly twice, in the barley genome. Treatment of dwarf mutants with gibberellic acid (GA3), or homozygosity at the ‘slender’ (sln1) locus, resulted in a 2.5‐fold (approximately) stimulation of blade elongation rate. Three of the five clones detected mRNAs that were maximally expressed towards the base of the blade, and present in greater quantities in GA3‐treated or slender seedlings. The remaining two clones detected mRNAs that were maximally expressed in the middle of the blade. Relative elemental growth rate (REGR) profiles of leaves growing with or without GA3 treatment revealed similar maximal REGR values despite a 2.5‐fold difference in leaf elongation rate. Segments of GA3‐treated leaves attained their maximal REGR values more rapidly, this being associated with enhanced expression of the three ‘basal’ XET‐related mRNAs. Highest XET activities were detected in the base of the elongation zone, and in GA3‐treated seedlings a second activity peak was observed near the distal end of the elongation zone. We conclude that there are likely to be several XET isoenzymes with different expression patterns, and identify those XET‐related proteins potentially involved in leaf elongation.
Directed overexpression of PHYA locally suppresses stem elongation and leaf senescence responses to far‐red radiation
Authors: ROUSSEAUX M. C. , BALLARÉ C. L. , JORDAN E. T. , VIERSTRA R. D. 
Published: November 2003

ABSTRACTEctopic overexpression of an oat PHYA cDNA in tobacco under the cauliflower mosaic virus 35S promoter results in plants with reduced morphological responses to far‐red radiation (FR). We have tested the hypothesis that it is possible to molecularly ‘mask’ steins and leaves to FR‐induced elongation and senescence responses by targeting the over‐expression of PHYA with appropriate promoters. Oat PHYA was expressed in tobacco (Nicotiana tabacum L. cv Xanthi) under the 35S and two Arabidopsis promoters: UBQ1 and CAB. The internodes of wild type, UBQ:PHYA, and CAB:PHYA plants, which exhibited little or no oat PHYA overexpression, responded to localized FR treatments with a marked increase in elongation. In contrast, 35S:PHYA plants, which overexpressed PHYA to high levels in all parts of the shoot, did not respond to FR treatments directed to their stems. Leaf senescence responses to FR were remarkably localized, and sensitivity to FR was also inversely correlated with the local PHYA expression level. Thus, chlorophyll content, specific leaf weight, and nitrate reductase activity in leaf spots treated with FR were highly reduced in wild type and UBQ:PHYA plants, but not in the CAB:PHYA and 35S:PHYA counterparts. Our results suggest that it may be feasible to obtain transgenic crop plants in which certain organs or tissues are made ‘blind’ to phytochrome‐perceived signals of canopy density, but whose general photomorphogenic competence is not greatly disturbed.
Photosynthetic responses to temperature of phosphoenolpyruvate carboxykinase type C4 species differing in cold sensitivity
Authors: MATSUBA K. , IMAIZUMI N. , KANEKO S. , SAMEJIMA M. , OHSUGI R. 
Published: November 2003

ABSTRACTPhotosynthetic rates, the activities of key enzymes associated with the C4 cycle and ribulose‐1,5‐bisphosphate carboxylase (RuBPCase), and the levels of metabolites involved in the C4 cycle were compared between the two phosphoenolpyruvate carboxykinase (PCK) type C4 species Spartina anglica, which is cold‐tolerant, and Zoysia japonica, which is cold‐sensitive, during exposure to low temperature. Plants of both species grown outside in summer were placed in a growth chamber at 27/20 °C day/night temperatures. After 1 week, plants were exposed to 20/17 °C for 1 week and then to 10/7 °C for 2 weeks. Photosynthetic rates in Z. japonica decreased progressively to about 25% during the chilling treatments. In contrast, S. anglica exhibited a 43% increase in photosynthetic rates after exposure to 20 °C for 1 week, which remained relatively constant thereafter. Consistent with these observations, most of the C4 enzymes and RuBPCase in Z. japonica declined. Phosphoenolpyruvate carboxylase (PEPC) and PCK activities declined particularly drastically during the treatments. However, the activities of these enzymes in S. anglica showed either a slight increase or decrease upon a mild cold treatment, and remained relatively constant during further chilling treatments. There was a sharp decline in phosphoenolpyruvate in Z. japonica after exposure to 10 °C. On the other hand, metabolite levels in S. anglica were largely unaffected by the chilling treatments. These results suggest that the drastic declines of both PEPC and PCK activities may be important limiting factors responsible for cold sensitivity in C4 photosynthesis of Z. japonica.
Effects of carbon dioxide concentration on the interactive effects of temperature and water vapour on stomatal conductance in soybean
Authors: WILSON K. B. , BUNCE J. A. 
Published: November 2003

ABSTRACTSoybeans were grown at three CO2 concentrations in outdoor growth chambers and at two concentrations in controlled‐environment growth chambers to investigate the interactive effects of CO2, temperature and leaf‐to‐air vapour pressure difference (LAVPD) on stomatal conductance. The decline in stomatal conductance with CO2 was a function of both leaf temperature and LAVPD. In the field measurements, stomatal conductance was more sensitive to LAVPD at low CO2 at 30 °C but not at 35 °C. There was also a direct increase in conductance with temperature, which was greater at the two elevated carbon dioxide concentrations. Environmental growth chamber results showed that the relative stomatal sensitivity to LAVPD decreased with both leaf temperature and CO2. Measurements in the environmental growth chamber were also performed at the opposing CO2, and these experiments indicate that the stomatal sensitivity to LAVPD was determined more by growth CO2 than by measurement CO2. Two models that describe stomatal responses to LAVPD were compared with the outdoor data to evaluate whether these models described adequately the interactive effects of CO2, LAVPD and temperature.
Growth and water‐use efficiency of 10 Triticum aestivum cultivars at different water availability in relation to allocation of biomass
Authors: VAN DEN BOOGAARD R. , ALEWIJNSE D. , VENEKLAAS E. J. , LAMBERS H. 
Published: November 2003

ABSTRACTIn environments where the amount of water is limiting growth, water‐use efficiency (biomass production per unit water use) is an important trait. We studied the relationships of plant growth and water use efficiency with the pattern of biomass allocation, using 10 wheat cultivars, grown at two soil moisture levels in a growth chamber. Allocation pattern and relative growth rate were not correlated, whereas allocation pattern and water use efficiency were. Variation in transpiration per plant resulted from variation in the rate of transpiration per unit leaf area or root weight, rather than from differences in leaf area or root weight per plant. Transpiration per unit leaf area or root weight was lower when the leaf area or root weight per unit plant weight was larger. Also, the efficiency of water use at the plant and leaf levels was higher for plants with a higher leaf area per unit plant weight, and it was not correlated with the plant's growth rate. Differences in water‐use efficiency at the leaf level were related to variation in stomatal conductance, rather than in the rate of photosynthesis. A high photosynthetic water‐use efficiency was associated with a low efficiency of nitrogen use for photosynthesis.
Evidence that inducible C4‐type photosynthesis is a chloroplastic CO2‐concentrating mechanism in Hydrilla, a submersed monocot
Authors: REISKIND J. B. , MADSEN T. V. , VAN GINKEL L. C. , BOWES G. 
Published: November 2003

ABSTRACT Hydrilla verticillata (L.f.) Royle exhibits an inducible C4‐type photosynthetic cycle, but lacks Kranz anatomy. Leaves in the C4‐type state (but not C3‐type) contained up to 5‐fold higher internal dissolved inorganic carbon (DIC) concentrations than the medium, indicating that they possessed a CO2‐concentrating mechanism (CCM). Several lines of evidence indicated that the chloroplast was the likely site of CO2 generation. From C4‐type leaf [DIC] measurements, the estimated chloroplastic free [CO2] was 400 mmol m−3. This gave a calculated 2% O2 inhibition of photosynthesis, which was identical to the measured value, and provided independent evidence that the estimated [CO2] was close to the true value. A homogeneous distribution of DIC in the C4‐type leaf could not account for such a high [CO2], or the resultant low O2 inhibition. For C3‐type leaves the estimated chloroplastic [CO2] was only 7 mmol m−3, which gave high, and similar, calculated and measured O2 inhibition values of 22 and 26%, respectively. The CCM did not appear to be located at the plasma membrane, as it operated at low and high pH, indicating that it was independent of use of HCO3− from the medium. Also, both C3− and C4‐type Hydrilla leaves showed pH polarity in the light, with abaxial and adaxial boundary layer values of about pH 4·0 and 10·5, respectively. Thus, pH polarity was not a direct component of the CCM, though it probably improved access to HCO3. Additionally, iodoacetamide and methyl viologen greatly reduced abaxial acidification, but not the steady‐state CCM. Inhibitor studies suggested that the CCM required photosynthetically generated ATP, but Calvin cycle activity was not essential. Both leaf types accumulated DIC in the dark by an ATP‐requiring process, possibly respiration, and C4‐type leaves fixed CO2 at 11·8% of the light rate. The operation of a CCM to minimize photorespiration, and the ability to recapture respiratory CO2 at night, would conserve DIC in a densely vegetated lake environment where daytime [CO2] is severely limiting, while [O2] and temperatures are high.
Effects of NO3−, NH4+ and urea nutrition on endogenous levels of IAA and four cytokinins in two epiphytic bromeliads
Authors: MERCIER H. , KERBAUY G.B. , SOTTA B. , MIGINIAC E. 
Published: November 2003

ABSTRACTThe long‐term effects of different nitrogen sources on the endogenous IAA and cytokinin levels in two bromeliad species were investigated. In nature, Vriesea philippocoburgii is a tank‐forming epiphytic bromeliad which uses the tank water reservoir as a substitute for soil, whereas Tillandsia pohliana is a tankless atmospheric epiphytic species. A culture was established from seeds germinated in aseptic condictions, and the plantlets were grown for 6 months in a modified Knudson medium to which was added 8 mol m−3 of nitrogen in the form of NO3−, NH4+ or urea. The hormonal contents of the bromeliad shoots were determined by means of high‐performance liquid chromatography (HPLC), coupled to an enzyme‐linked immunosorbent assay (ELISA) for indole‐3‐acetic acid (IAA), isopentenyladenine (iP), isopentenyladenosine ([9R]iP), zeatin (Z) and zeatin riboside ([9R]Z). Nitrogen supplied in the form of urea gave the highest values of fresh and dry weights for both species, and this was positively correlated to IAA levels. The cytokinin patterns showed that isopentenyladenosine was the predominant form for both species in all samples. However, urea induced the highest level of this riboside form and also the highest level of total cytokinins for V. philippocoburgii, while NH4+ had the same effect on the atmospheric species. These results are discussed in terms of the different growth habits of these two species in nature. It is suggested that urea may be an important source of nitrogen often found inside the tank of V. philippocoburgii. NO3− treatment increased the IAA/Cks balance, mainly for V. philippocoburgii, while urea and NH4+ shifted this ratio in favour of cytokinins, thus apparently inhibiting root development in both species.
Protoplast hexose carrier activity is a determinate of genotypic difference in hexose storage in tomato fruit
Authors: RUAN Y.‐L. , PATRICK J.W. , BRADY C. 
Published: November 2003

ABSTRACTPost‐phloem sugar transport in developing tomato (Lycopersicon esculentum Mill. cv. Flora‐Dade) fruit follows an apoplastic route during the rapid phase of sugar accumulation. The pathway is characterized by sugar retrieval by the storage parenchyma cells from the fruit apoplast. Two tomato genotypes differing in fruit hexose content were compared in terms of the transport and transfer processes controlling fruit sugar levels. The genotypic difference in fruit sugar content was independent of photoassimilate export from source leaves. Discs of pericarp tissue were cultured in a medium based on analyses of the fruit apoplastic sap. The cultured discs maintained a composition, a relative growth rate and a respiration rate similar to those of the pericarp tissue of intact fruit. Estimates of hexose fluxes into metabolic and storage pools suggested that membrane transport regulated the genotypic difference in hexose accumulation. Short‐term [14C]hexose uptake experiments demonstrated a genotypic difference in Vmax for glucose, fructose and 3‐O‐methyl‐glucose, and this difference was abolished in the presence of the inhibitor p‐chloromercuribenzenesulphonic acid (PCMBS). The results support the hypothesis that the activity of energized hexose carriers on the plasma membranes of storage parenchyma cells is a significant determinate of the genotypic difference in hexose accumulation.
Stomatal responses to changes in air humidity are not necessarily linked to nocturnal CO2 uptake in the CAM plant Plectranthus marrubioides Benth. (Lamiaceae)
Authors: HERPPICH W. B. 
Published: November 2003

ABSTRACTPlants of the crassulacean acid metabolism (CAM) species Plectranthus marrubioides (Lamiaceae) were subjected to short‐ and long‐term changes in air humidity in controlled‐environment experiments. Stomata of well‐watered individuals of this all‐cell leaf‐succulent taxon responded directly, quickly and reversibly to variations of the water vapour gradient between leaf and air (Δw). Mean night‐time leaf conductance to water vapour decreased curvilinearly with increasing Δw but linearly with lowered relative air humidity. Stomatal response was generally independent of the prevailing temperature and was not linked to CO2 uptake rates. Therefore, net night‐time carbon gain, nocturnal malic acid accumulation and, thus, relative carbon recycling were not influenced by changes in air humidity in the temperature range tested. Mean nocturnal molar water use efficiency, however, decreased with decreasing air humidity because of the increased transpirational water loss. If watering was repeatedly withheld for several days during the experiments, employing a temperature regime of 35/30°C day and night, stomatal conductance became low enough to inhibit CO2 uptake, but only at the highest Δw. The results suggest that drought stress was necessary to increase responsiveness of plants to the point where CAM was also inhibited by decreases in air humidity.
EPR evidence for superoxide anion formation in leaves during exposure to low levels of ozone
Authors: RUNECKLES V. C. , VAARTNOU M. 
Published: November 2003

ABSTRACTAlthough the superoxide anion radical (O) has been implicated in the phytotoxicity of ozone, (O3), its role has been inferred from indirect evidence based on the activity of oxyradical scavenging systems in the leaf, particularly superoxide dismutase (SOD). Direct observations of radical signals obtained by electron paramagnetic resonance spectrometry (EPR) of intact, attached leaves of bluegrass (Poa pratensis L.) and ryegrass (Lolium perenne L.) and leaf pieces of radish (Raphanus sativus L.) during exposure to 240 μg m−3 O3 in air flowing through the spectrometer cavity have revealed the appearance of a signal with the characteristics of O. The exposures used were insufficient to cause any necrotic injury to the leaves. The appearance of the signal is light‐dependent, suggesting that it originates in the chloroplast, and its appearance is reduced in leaves in which the apoplastic pool of ascorbic acid has been enriched by prior vacuum infiltration. In each species, the signal only appeared after about 1 h of exposure to O3, and then increased steadily over the next 4 h. The lability of the species responsible for the signal is such that it can no longer be reliably detected about 15 min after cessation of the exposure to O3. These observations are interpreted as indicating that apoplastic ascorbate initially reduces the production of O, probably by reducing the penetration of O3 into the cell, with any O produced being scavenged by the chloroplastic SOD‐per‐oxidase system, but its formation from O3 then begins to exceed the capacity of the scavenging systems to remove it.
Fluxes of carbon, water and energy over Brazilian cerrado: an analysis using eddy covariance and stable isotopes
Authors: MIRANDA A. C. , MIRANDA H. S. , LLOYD J. , GRACE J. , FRANCEY R. J. , MCINTYRE J. A. , MEIR P. , RIGGAN P. , LOCKWOOD R. , BRASS J. 
Published: November 2003

ABSTRACTWe present the energy and mass balance of cerrado sensu stricto (a Brazilian form of savanna), in which a mixture of shrubs, trees and grasses forms a vegetation with a leaf area index of 1·0 in the wet season and 0·4 in the dry season. In the wet season the available energy was equally dissipated between sensible heat and evaporation, but in the dry season at high irradiance the sensible heat greatly exceeded evaporation. Ecosystem surface conductance gs in the wet season rose abruptly to 0·3 mol m−2 s−1 and fell gradually as the day progressed. Much of the total variation in gs was associated with variation in the leaf‐to‐air vapour pressure deficit of water and the solar irradiance. In the dry season the maximal gs values were only 0·1 mol m−2 s−1. Maximal net ecosystem fluxes of CO2 in the wet and dry season were –10 and –15 μmol CO2 m−2 s−1, respectively (sign convention: negative denotes fluxes from atmosphere to vegetation). The canopy was well coupled to the atmosphere, and there was rarely a significant build‐up of respiratory CO2 during the night. For observations in the wet season, the vegetation was a carbon dioxide sink, of maximal strength 0·15 mol m−2 d−1. However, it was a source of carbon dioxide for a brief period at the height of the dry season. Leaf carbon isotopic composition showed all the grasses except for one species to be C4, and all the palms and woody plants to be C3. The CO2 coming from the soil had an isotopic composition that suggested 40% of it was of C4 origin.
Is glycine betaine a non‐compatible solute in higher plants that do not accumulate it?
Authors: GIBON Y. , BESSIERES M. A. , LARHER F. 
Published: November 2003

ABSTRACTRape (Brassica napus L. var. oleifera cv. Samourai) leaf discs treated in vitro in the presence of glycine betaine (GB) exhibited very high accumulation of GB, suggesting the operation of a specific uptake system. When further subjected to osmotic upshocks by transfer to PEG 6000 media, the typical osmo‐induced proline response of the discs was strongly inhibited. The level of this inhibition was quantitatively related to the amount of GB loaded in the tissues. In contrast, the soluble sugar content increased in GB‐treated discs. Surprisingly, viability tests (i.e. membrane stability and 2,3,5‐triphenyltetrazolium chloride reduction) indicated a destabilizing effect of GB in these tissues. This is at variance with the relative compatibility of sucrose and proline. In addition, the protein content was lower in GB‐treated discs. This could be related to an inhibitory effect on protein synthesis, as demonstrated by radiolabelling of polypeptides with [35S] amino acids. This effect was particularly pronounced on Rubisco large sub‐unit synthesis and was still apparent under non‐stress conditions. The GB treatment was also followed by the induction or up‐regulation of a set of polypeptides, not seen under stress conditions, while the synthesis of osmo‐induced polypeptides was not affected by GB. These novel effects of GB lead us to discuss the reasons for its incompatibility in leaf tissues of a non‐GB‐accumulating species.
Potato plants contain multiple forms of sucrose phosphate synthase, which differ in their tissue distributions, their levels during development, and their responses to low temperature
Authors: REIMHOLZ R. , GEIGER M. , HAAKE V. , DEITING U. , KRAUSE K.‐P. , SONNEWALD U. , STITT M. 
Published: November 2003

ABSTRACTAntibodies raised against a peptide fragment (residues 60–456) of potato sucrose phosphate synthase (SPS) were used to investigate whether potato plants contain multiple forms of SPS. When a partially purified preparation of SPS from cold‐stored potato tubers was separated on 5% polyacrylamide gel electrophoresis (PAGE), four immunopositive bands were found with estimated molecular weights of 125, 127, 135 and 145 kDa. These bands were also found in rapidly prepared extracts and were termed SPS‐1a, SPS‐1b, SPS‐2 and SPS‐3, respectively. Direct evidence that SPS‐1a and SPS‐1b represent active SPS was provided by the finding that both are greatly reduced in plants expressing an antisense sequence derived from the potato leaf SPS gene. SPS‐2 was not decreased in the antisense plants, indicating that it has a significantly different sequence. Evidence that SPS‐2 represents active SPS was obtained by showing that the amount of SPS‐1a and SPS‐1b protein remaining in the leaves and tubers of antisense potato plants was too low to account for the remaining SPS activity. The four immunopositive SPS forms had different tissue distributions. SPS‐1a was the major form in all tissues except petals, sepals and stamens. SPS‐1b and SPS‐2 were absent in very young growing tissues but were present as minor forms in source leaves and sprouting tubers. The SPS‐1b level was especially high in petals and sepals, and the SPS‐2 level was especially high in the stamens. SPS‐3 was only detected in very young tissues. The four forms also showed different responses to low temperature. Transfer of tubers to 4°C led to a specific and reversible increase of SPS‐1b during the next 4 d. The appearance of SPS‐1b correlated with a change in the kinetic properties of SPS that has recently been shown (Hill et al. 1996) to play a key role in triggering the accumulation of sugars in cold‐stored tubers. The appearance of SPS‐1b protein at low temperature was accompanied by an increase of SPS transcript. Incubation of tuber slices with calyculin A and okadaic acid to alter the phosphorylation state of SPS did not lead to appearance or disappearance of SPS‐1b. It is concluded that potato plants contain several forms of SPS that have different functions in growing and mature tissues, in flower parts, and in acclimation to low temperature.