bluuebunny/crossref_metadata_2025_split huggingface dataset:
A possible optical role of the bundle sheath extensions of the heterobaric leaves ofVitis viniferaandQuercus coccifera
Authors: Karabourniotis G. , Bornman J. F. , Nikolopoulos D. 
Published: March 2003

ABSTRACTHeterobaric leaves are characterized by transparent regions in their lamina, due to the occurrence of bundle sheath extensions. Fused silica fibre‐optic microprobes were used to monitor light gradients and part of the spectral regime along the bundle sheath extensions, as well as along the mesophyll in the heterobaric leaves of two representative plants, one mesomorphic (Vitis viniferaL.) and one xeromorphic (Quercus cocciferaL.). It was found that the attenuation of collimated visible light by the bundle sheath extensions of both plants was weaker than the attenuation by the photosynthetic parenchyma layers. However, only a small portion of the amount of light that strikes the leaf surface is transmitted through these structures. The adaxial epidermis covering the bundle sheath extensions, as well as the mesophyll, afforded similar effective protection against UV radiation in both tissues. The relative amount of the forward‐scattered visible light inside the bundle sheath extensions approached that detected by the microprobe at the adaxial illuminated leaf surface. Moreover, light transmitted through the bundle sheath extensions was enriched mainly in the blue and red regions, compared to light transmitted through the photosynthetic tissue. The time course of photosynthetic starch formation in the leaves ofV. viniferadetected by iodine staining showed that the accumulation of starch during the first minutes of illumination was high within photosynthetic parenchyma cells adjacent to the bundle sheath extensions. The data showed that bundle sheath extensions act as transparent ‘windows’ which enrich the neighbouring mesophyll areas with high levels of photosynthetically active radiation (400–700 nm). The phenomenon was more pronounced in the thick and compact sclerophyllous leaves ofQ. cocciferaby virtue of the greater abundance of bundle sheath extensions as compared to that inV. vinifera.The enhancement of the light micro‐environment within the deep internal layers of the mesophyll may affect the photosynthetic performance of such leaves, giving adaptive advantages.
Nitrate reductase in Zea mays L. under salinity
Authors: Baki G. K. Abd‐El , Siefritz F. , Man H.‐M. , Weiner H. , Kaldenhoff R. , Kaiser W. M. 
Published: March 2003

ABSTRACTYoung maize seedlings (Zea mays L. cv.Giza 2) were exposed to moderate salinity in hydroponic culture. NADH‐nitrate reductase (NR) activity (E.C. 1·6.6·1), NR activation state, NR‐mRNA‐steady state levels and major solute contents in leaves and roots were investigated. With increasing external salt concentration, Na+, Cl−, sugars, amino acids and quarternary ammonium compounds accumulated in leaves and roots, with concentrations in leaves exceeding those in roots. The nitrate content of leaves decreased, but increased in roots. The diurnal pattern of NR activity and of NR‐mRNA was also changed under salinity, but the NR activation state was not affected. In the first light phase, maximum NR activity increased rapidly in leaves of control plants, but was much slower in leaves from salinized plants. Thus, integrated over the whole day, the NR activity of salt‐stressed plants was lower than in control plants. NR transcript levels of control plants were low in the early night phase, started to increase in the second night phase, followed by a distinct peak at 2 h into the light period. This large ‘early morning peak’ of NR‐mRNA was hardly affected by salinity, whereas the initial slow increase of m‐RNA levels in the early night phase was almost absent in salinized plants. This is considered as one reason for the low NR activity of salinized plants in the first half of the day. It is also suggested that nitrate is a major signal affecting NR expression and activity under salinity. Sugars and amino acids appeared less important.
The role of genes influencing the corolla in pollination of Antirrhinum majus
Authors: Comba L. , Corbet S. A. , Hunt H. , Outram S. , Parker J. S. , Glover B. J. 
Published: March 2003

ABSTRACTStudies of pollination ecology have been hindered by an absence of biochemical information about the basis of polymorphism. Using model plants and mutant lines described by molecular genetics may circumvent this difficulty. Mutation of genes controlling petal colour and petal epidermal cell shape in Antirrhinum majus was previously shown to influence fruit set. White flowers set less fruit than magenta flowers and mutants with flat petal epidermal cells set less fruit than flowers with conical cells. Here we analyse the causal pathway underlying this phenomenon through a study of floral characteristics and bee behaviour. Results indicate that bees recognized plants with magenta conical‐celled flowers at a distance and did not approach white flowers or magenta flat‐celled flowers so frequently. Petal cell shape interacted with colour in determining whether an approaching bee landed on a flower within a plot and whether a bee landing on a flower would probe it. The intrafloral temperature of flowers with conical petal cells was shown to increase with solar irradiance, unlike the intrafloral temperature of flowers with flat petal cells. The difference in fruit set may reflect pollinator discrimination between genotypes as a consequence of the effect of intrafloral temperature on nectar quality and quantity.
Olive phenology as a sensitive indicator of future climatic warming in the Mediterranean
Authors: Osborne C. P. , Chuine I. , Viner D. , Woodward F. I. 
Published: March 2003

ABSTRACTExperimental and modelling work suggests a strong dependence of olive flowering date on spring temperatures. Since airborne pollen concentrations reflect the flowering phenology of olive populations within a radius of 50 km, they may be a sensitive regional indicator of climatic warming. We assessed this potential sensitivity with phenology models fitted to flowering dates inferred from maximum airborne pollen data. Of four models tested, a thermal time model gave the best fit for Montpellier, France, and was the most effective at the regional scale, providing reasonable predictions for 10 sites in the western Mediterranean. This model was forced with replicated future temperature simulations for the western Mediterranean from a coupled ocean‐atmosphere general circulation model (GCM). The GCM temperatures rose by 4·5 °C between 1990 and 2099 with a 1% per year increase in greenhouse gases, and modelled flowering date advanced at a rate of 6·2 d per °C. The results indicated that this long‐term regional trend in phenology might be statistically significant as early as 2030, but with marked spatial variation in magnitude, with the calculated flowering date between the 1990s and 2030s advancing by 3–23 d. Future monitoring of airborne olive pollen may therefore provide an early biological indicator of climatic warming in the Mediterranean.
Cell wall pectin content modulates aluminium sensitivity of Zea mays (L.) cells grown in suspension culture
Authors: Schmohl N. , Horst W. J. 
Published: March 2003

ABSTRACTThe pectin content of the cell walls of maize suspension cells was modified to investigate its role in the expression of aluminium (Al) toxicity. Long‐term adaptation to NaCl or to the cellulose synthesis inhibitor 2,6‐dichlorbenzonitirle (DCB) increased the pectin content by 31 and 86%, respectively. Subculturing salt‐adapted cells for up to 3 weeks without NaCl supply or treatment of cells with pectolyase for up to 15 min reduced pectin contents by up to 46%. Such pre‐cultured cells were incubated for 2 h in presence of Al. There was a close positive correlation between pectin and both total and BaCl2 non‐exchangeable Al contents. Aluminium‐induced callose formation as an indicator of Al injury was closely positively correlated to the loss of cell viability. In NaCl‐adapted and pectolyase‐treated cells, Al‐induced callose formation was reduced when compared with normal cells. However, there was a close positive relationship between pectin contents and relative callose induction (digitonin‐induced callose formation, reflecting the different capabilities of cells to synthesize callose set to 100%) indicating that cells with higher pectin contents are more Al‐sensitive. The results presented support our view that the binding of Al to the cell wall pectin‐matrix represents an important step in the expression of Al toxicity.
Photosynthetic performance at low temperature ofBouteloua gracilisLag., a high‐altitude C4grass from the Rocky Mountains, USA
Authors: Pittermann J. , Sage R. F. 
Published: March 2003

ABSTRACTThe mechanisms controlling the photosynthetic performance of C4plants at low temperature were investigated using ecotypes ofBouteloua gracilisLag. from high (3000 m) and low (1500 m) elevation sites in the Rocky Mountains of Colorado. Plants were grown in controlled‐environment cabinets at a photon flux density of 700μmol m−2s−1and day/night temperatures of 26/16 °C or 14/7 °C. The thermal response of the net CO2assimilation rate (A) was evaluated using leaf gas‐exchange analysis and activity assays of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPCase) and pyruvate,orthophosphate dikinase (PPDK). In both ecotypes, a reduction in measurement temperature caused the CO2‐saturated rate of photosynthesis to decline to a greater degree than the initial slope ofAversus the intercellular CO2response, thereby reducing the photosynthetic CO2saturation point. As a consequence,Ain normal air was CO2‐saturated at sub‐optimal temperatures. Ecotypic variation was low when grown at 26/16 °C, with the major difference between the ecotypes being that the low‐elevation plants had higherA;however, the ecotypes responded differently when grown at cool temperature. At temperatures below the thermal optimum,Ain high‐elevation plants grown at 14/7 °C was enhanced relative to plants grown at 26/16 °C, whileAin low‐elevation plants grown at 14/7 °C was reduced compared to 26/16 °C‐grown plants. Photoinhibition at low growth temperature was minor in both ecotypes as indicated by small reductions in dark‐adaptedFv/Fm. In both ecotypes, the activity of Rubisco was equivalent toAbelow 17 °C but well in excess ofAabove 25 °C. Activities of PEPCase and PPDK responded to temperature in a similar proportion relative to Rubisco, and showed no evidence for dissociation that would cause them to become principal limitations at low temperature. Because of the similar temperature response of Rubisco andA, we propose that Rubisco is a major limitation on C4photosynthesis inB. gracilisbelow 17 °C. Based on these results and for theoretical reasons associated with how C4plants use Rubisco, we further suggest that Rubisco capacity may be a widespread limitation upon C4photosynthesis at low temperature.
The effects of moisture and temperature on the ageing kinetics of pollen: interpretation based on cytoplasmic mobility
Authors: Buitink J. , Leprince O. , Hemminga M. A. , Hoekstra F. A. 
Published: March 2003

ABSTRACTThis study shows that characterization of the molecular mobility in the cytoplasm of pollen provides a new understanding of the effects of moisture and temperature on ageing rates. Using EPR spectroscopy, we determined the rotational motion of the polar spin probe, 3‐carboxy‐proxyl, in the cytoplasm of Typha latifolia pollen, under different temperature and moisture content conditions. Increasing the temperature resulted in faster rotational motion, analogous to faster ageing rates. With decreasing moisture content, rotational motion first decreased until a minimum was reached, after which rotational motion slightly increased again. The moisture content at which this minimal rotational motion was observed increased with decreasing temperature, comparable to the pattern of ageing rate. A significant linear relationship was found between ageing rates and rotational motion in the cytoplasm, suggesting that these parameters are causally linked. Upon melting of the intracellular glass, a twofold increase in activation energy of rotational motion and ageing rate was observed. In contrast, melting of the sucrose glass resulted in an increase in rotational motion of five orders of magnitude. The difference in rotational motion upon melting glasses of pollen or sucrose suggests that other molecules beside sugars play a role in intracellular glass formation in pollen.
Tolerance of pea (Pisum sativum L.) to long‐term salt stress is associated with induction of antioxidant defences
Authors: Hernández J. A. , Jiménez A. , Mullineaux P. , Sevilia F. 
Published: March 2003

ABSTRACTUsing two cultivars of Pisum sativum L. with different sensitivity to NaCl, the effect of long‐term (15 d) NaCl (70 m
M) treatments on the activity and expression of the foliar ascorbate–glutathione cycle enzymes, superoxide dismutase isozymes and their mRNAs was evaluated and related to their ascorbate and glutathione contents. High‐speed supernatant (soluble) fractions, enriched for cytosolic components of the antioxidant system, were used. In this fraction from the NaCl‐tolerant variety (cv Granada), the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), Mn‐superoxide dismutase (Mn‐SOD) and dehydroascorbate reductase (DHAR) increased, while CuZn‐SOD activity remained constant. In the NaCl‐sensitive plants (cv Challis), salinity did not produce significant changes in APX, MDHAR and GR activities. Only DHAR activity was induced in cv Challis, whereas soluble CuZn‐SOD activity decreased by about 35%. Total ascorbate and glutathione contents decreased in both cultivars, but the decline was greater in NaCl‐sensitive plants. This difference between the two cultivars was more pronounced when the transcript levels of some these enzymes were examined. Transcript levels for mitochondrial Mn‐SOD, chloroplastic CuZn‐SOD and phospholipid hydroperoxide glutathione peroxidase (PHGPX), cytosolic GR and APX were strongly induced in the NaCl‐tolerant variety but not in the NaCl‐sensitive variety. These data strongly suggest that induction of antioxidant defences is at least one component of the tolerance mechanism of peas to long‐term salt‐stress.
Influence of nutrient versus water supply on hydraulic architecture and water balance in Pinus taeda
Authors: Ewers B. E. , Oren R. , Sperry J. S. 
Published: March 2003

ABSTRACTWe investigated the hydraulic consequences of a major decrease in root‐to‐leaf area ratio (AR:AL) caused by nutrient amendments to 15‐year‐old Pinus taeda L. stands on sandy soil. In theory, such a reduction in AR:AL should compromise the trees’ ability to extract water from drying sand. Under equally high soil moisture, canopy stomatal conductance (GS) of fertilized trees (F) was 50% that of irrigated/fertilized trees (IF), irrigated trees (I), and untreated control trees (C). As predicted from theory, F trees also decreased their stomatal sensitivity to vapour pressure deficit by 50%. The lower GS in F was associated with 50% reduction in leaf‐specific hydraulic conductance (KL) compared with other treatments. The lower KL in F was in turn a result of a higher leaf area per sapwood area and a lower specific conductivity (conducting efficiency) of the plant and its root xylem. The root xylem of F trees was also 50% more resistant to cavitation than the other treatments. A transport model predicted that the lower AR:AL in IF trees resulted in a considerably restricted ability to extract water during drought. However, this deficiency was not exposed because irrigation minimized drought. In contrast, the lower AR:AL in F trees caused only a limited restriction in water extraction during drought owing to the more cavitation resistant root xylem in this treatment. In both fertilized treatments, approximate safety margins from predicted hydraulic failure were minimal suggesting increased vulnerability to drought‐induced dieback compared with non‐fertilized trees. However, IF trees are likely to be so affected even under a mild drought if irrigation is withheld.
Plasticity in relative growth rate and its components following a change in irradiance
Authors: Shipley B. 
Published: March 2003

ABSTRACTA total of 244 plants from two species, Lythrum salicaria and Epilobium glandulosum, were grown individually in hydroponic sand culture from seed for 36 d. Until day 27 all plants experienced an irradiance of 550 μmol m−2 s−1 PFD and on day 27 half of the plants were subjected to a neutral shade treatment in which irradiance was reduced to 100 μmol m−2 s−1 photon fluy density (PFD). Measures of relative growth rate, net assimilation rate, specific leaf area, biomass partitioning to leaves, roots, structural tissues (i.e. stems, petioles and inflorescences) and tissue density were obtained from intensive harvests three or four times per day. The shade treatment caused an immediate decrease in relative growth rate and net assimilation rate. Within hours the specific leaf area of the shaded plants increased and leaf tissue density decreased, thus partially offsetting the decrease in relative growth rate. Biomass partitioning was not affected.
Metabolic regulation and gene expression of root phosphoenolpyruvate carboxylase by different nitrogen sources
Authors: Pasqualini S. , Ederli L. , Piccioni C. , Batini P. , Bellucci M. , Arcioni S. , Antonielli M. 
Published: March 2003

ABSTRACTAlfalfa (Medicago sativaL.) N‐sufficient plants were fed 1·5 mMN in the form of NO3−, NH4+or NO3−in conjunction with NH4+, or were N‐deprived for 2 weeks. The specific activity of phosphoenolpyruvate carboxylase (PEPC) from the non‐nodulated roots of N‐sufficient plants was increased in comparison with that of N‐deprived plants. The PEPC value was highest with NO3−nutrition, lowest with NH4+and intermediate in plants that were fed mixed salts. The protein was more abundant in NO3−‐fed plants than in either NH4+‐ or N mixed‐fed plants. Nitrogen starvation decreased the level of PEPC mRNA, and nitrate was the N form that most stimulated PEPC gene expression. The malate content was significantly lower in NO3−‐deprived than in NO3−‐sufficient plants. Root malate accumulation was high in NO3−‐fed plants, but decreased significantly in plants that were fed with NH4+. The effect of malate on the desalted enzyme was also investigated. Root PEPC was not very sensitive to malate and PEPC activity was inhibited only by very high concentrations of malate. Asparagine and glutamine enhanced PEPC activity markedly in NO3−‐fed plants, but failed to affect plants that were either treated with other N types or N starved. Glutamate and citrate inhibited PEPC activity only at optimal pH. N‐nutrition also influenced root nitrate and ammonium accumulation. Nitrate accumulated in the roots of NO3−‐ and (NO3−+ NH4+)‐fed plants, but was undetectable in those administered NH4+. Both the nitrate and the ammonium contents were significantly reduced in NO3−‐ and (NO3−+ NH4+)‐starved plants. Root accumulation of free amino acids was strongly influenced by the type of N administered. It was highest in NH4+‐fed plants and the most abundant amides were asparagine and glutamine. It was concluded that root PEPC from alfalfa plants is N regulated and that nitrate exerts a strong influence on the PEPC enzyme by enhancing both PEPC gene expression and activity.
The differential expression of a heat shock promoter in floral and reproductive tissues
Authors: Crone D. , Rueda J. , Martin K. L. , Hamilton D. A. , Mascarenhas J. P. 
Published: March 2003

AbstractA detailed histochemical analysis of the expression of the soybean small heat shock protein gene promoter, GmHSP 17·5E, fused to the GUS reporter gene, has been made in all organs and tissues of the flower as a function of stage of development and heat stress. This promoter is not uniformly expressed after a heat shock in all floral tissues and organs. Expression is seen at all stages of development in the sepals but not in the petals. The expression pattern in the pistil and in anthers is complex. Heat stress‐induced GUS staining is seen in the style and upper portion of the ovary, but not in the stigmatic papillae or in the lower part of the ovary or in ovules. In stamens the heat shock response is seen in the filament and in the extension of the vascular tissue from the filament into the anther. No induction is seen in other tissues of the anther or in microspores or pollen at any stage of development. Vegetative organs in contrast are more uniform in the heat shock inducibility of GUS activity. Based on evidence from transient assays after microprojectile particle bombardment of the GmHSP 17·5E/GUS construct into pollen, it is likely that the gene is transcriptionally in an inactive configuration in pollen nuclei in stably transformed transgenic plants. These results are discussed with reference to other information in the literature.
Direct evidence for non‐enzymatic fragmentation of chloroplastic glutamine synthetase by a reactive oxygen species
Authors: Ishida H. , Anzawa D. , Kokubun N. , Makino A. , Mae T. 
Published: March 2003

AbstractChloroplastic glutamine synthetase (GS: EC 6·3·1·2), the octamer of the 44 kDa subunit, is rapidly degraded under photo‐oxidative stress conditions in leaves, chloroplasts, and chloroplast lysates. Recent studies have suggested that chloroplastic GS might be cleaved by the hydroxyl radical under such conditions (Thoenen & Feller 1998; Australian Journal of Plant Physiology 25, 279–286; Palatnik, Carrillo & Valle 1999, Plant Physiology 121, 471–478). Herein, we present evidence which supports the above hypothesis. When the purified GS from wheat (Triticum aestivum L.) chloroplasts was exposed to the hydroxyl radical‐generating system comprising H2O2–FeSO4–ascorbic acid or FeCl3–ascorbic acid, the GS subunit was degraded into four distinct fragments having apparent molecular masses of 39, 35, 32 and 28 kDa. The apparent molecular masses and isoelectric points of these fragments were identical to those of the respective fragments found in the illuminated lysates of chloroplasts. In addition, the appearance of the GS fragments was completely suppressed in the presence of the scavenger for the hydroxyl radical, n‐propyl gallate, in the illuminated lysates of chloroplasts. These results strongly support the hypothesis that the primary cleavage of GS is directly driven by the hydroxyl radical, formed by Fenton reaction under photo‐oxidative stress conditions in chloroplasts.