bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diurnal and developmental changes in levels of nucleotide compounds in developing maize endosperms
Authors: Scott M. P. 
Published: March 2003

ABSTRACTMaize endosperm is dependent on source tissues to supply the energy and carbon required for development. This supply varies during the course of each day and also throughout development. The impact of these variations on the metabolism of developing endosperm was examined by determining the energy status of the endosperm throughout the course of a day. The adenylate energy charge decreased as the tissue matured, and exhibited a distinct diurnal pattern, reaching a minimum in the afternoon, when the flux of photosynthate is the highest. The minimum value observed was similar to the adenylate energy charge in tissues under mild stress. As the endosperm matured, the adenylate energy charge decreased steadily. The levels of the polysaccharide precursors ADP‐glucose and UDP‐glucose did not reflect the daily fluctuations in adenylate energy charge, but did exhibit similar long‐term behaviour in the latter half of development, decreasing steadily after 21 d after pollination. Similarities in the metabolic patterns of adenylate and uridylate nucleotide levels are discussed in terms of the analogous roles of these compounds in starch and cellulose biosynthesis, respectively. These data provide insight into the metabolic rhythms occurring during endosperm development, and provide a framework for efforts directed toward metabolic engineering.
Regulatory roles of benzyl adenine and sucrose during wound response of the ribosomal protein gene, rpL34
Authors: Yu G.‐H. , An G. 
Published: March 2003

ABSTRACTWe previously reported that a large subunit ribosomal protein gene, rpL34, was wound‐inducible in tobacco leaves, and that benzyl adenine (BA) enhanced the wound‐inducible expression of the gene. Here we report that the wound‐inducible expression of the rpL34 gene is enhanced by sucrose. The regulatory roles of BA and sucrose in wound‐signalling pathways were investigated using transgenic plants expressing a fusion molecule between the rpL34 promoter and the chloramphenicol acetyltransferase (cat) gene. Wounding caused a progressive increase in CAT activity; BA and sucrose enhanced the response. This indicates that regulation occurs at the transcriptional level. Diethyldithiocarbamic acid (DIECA) and other potent inhibitors of the octadecanoid pathway inhibited the rpL34 promoter, and also reduced BA inducibility of that wound response. However, inhibitors of the octadecanoid pathway did not affect the sucrose response. Protein kinase inhibitors increased BA enhancement while decreasing the sucrose effect, suggesting that protein kinases differentially regulate BA‐ and sucrose‐signalling in the promoter's wound response. Taken together, BA and sucrose enhanced the wound response of the rpL34 promoter via different signalling pathways, although they exerted overlapping effects on wound‐induction of the promoter.
Discrimination of nitrogen isotopes during absorption of ammonium and nitrate at different nitrogen concentrations by rice (Oryza sativa L.) plants
Authors: Yoneyama T. , Matsumaru T. , Usui K. , Engelaar W. M. H. G. 
Published: March 2003

ABSTRACTStudies of uptake of ionic sources of N by two hydroponically grown rice (Oryza sativa L.) cultivars (paddy‐field‐adapted Koshihikari and dryland‐adapted Kanto 168) showed that the magnitude of the nitrogen isotope fractionation (ɛ) for uptake of NH4+ depended on the concentrations of NH4+ and cultivar (averaging –6·1‰ for Koshihikari and –12·0‰ for Kanto 168 at concentrations from 40 to 200 mmol m−3 and, respectively, –13·4 and –28·9‰ for the two cultivars at concentrations from 0·5 to 4 mol m−3). In contrast, the ɛ for uptake of NO3− in similar experiments was almost insensitive to the N concentration, falling within a much narrower range (+3·2‰ to –0·9‰ for Koshihikari and –0·9‰ to –5·1‰ for Kanto 168 over NO3− concentrations from 0·04 to 2 mol m−3). From longer term experiments in which Norin 8 and its nitrate‐reductase deficient mutant M819 were grown with 2 or 8 mol m−3 NO3− for 30 d, it was concluded that the small concentration‐independent isotopic fractionation during absorption of this ion was not related to nitrate reductase activity.
Maturation of integrated functions during development. I. Modifications of the regulatory network during transition periods in Sorghum bicolor
Authors: Amzallag G. N. 
Published: March 2003

ABSTRACTGibberellin (GA) and cytokinin (CK) were exogenously supplied at different periods of the vegetative development in Sorghum bicolor. Growth response to these hormonal treatments differed according to the developmental stage. This reveals the existence of discrete phenophases, each one characterized by a specific sensitivity to plant growth regulations (PGRs). Developmental changes in sensitivity were less accentuated in plants grown in optimal conditions than in plants exposed to 150 mM NaCl. Variations in organ connectance (the level of coordination in growth of the shoot, adventitious roots and seminal root) were analysed during vegetative growth of salt‐treated plants. This analysis shows a temporary decrease in connectance during the transition period between phenophases. From the effect of hormonal treatments on connectance, it was concluded that (i) the transition period coincides with a partial dismantling of the initial regulatory network followed by the emergence of a new network coordinating growth of the different organs; (ii) GA is involved in the process of emergence of a transition period; and (iii) duration of the transition period is considerably enlarged for plants exposed to NaCl stress. This dynamics of alternance of phenophase and transition periods enables the integration of the two modes of action of the PGRs (dose–response and change in sensitivity) within a unified framework.
RATP: a model for simulating the spatial distribution of radiation absorption, transpiration and photosynthesis within canopies: application to an isolated tree crown
Authors: Sinoquet H. , Le Roux X. , Adam B. , Ameglio T. , Daudet F. A. 
Published: March 2003

ABSTRACTThe model RATP (radiation absorption, transpiration and photosynthesis) is presented. The model was designed to simulate the spatial distribution of radiation and leaf‐gas exchanges within vegetation canopies as a function of canopy structure, canopy microclimate within the canopy and physical and physiological leaf properties. The model uses a three‐dimensional (3D) representation of the canopy (i.e. an array of 3D cells, each characterized by a leaf area density). Radiation transfer is computed by a turbid medium analogy, transpiration by the leaf energy budget approach, and photosynthesis by the Farquhar model, each applied for sunlit and shaded leaves at the individual 3D cell‐scale. The model typically operates at a 20–30 min time step. The RATP model was applied to an isolated, 20‐year‐old walnut tree grown in the field. The spatial distribution of wind speed, stomatal response to environmental variables, and light acclimation of leaf photosynthetic properties were taken into account. Model outputs were compared with data acquired in the field. The model was shown to simulate satisfactorily the intracrown distribution of radiation regime, transpiration and photosynthetic rates, at shoot or branch scales.
Effects of high‐temperature stress on microsporogenesis in heat‐sensitive and heat‐tolerant genotypes of Phaseolus vulgaris
Authors: Porch T. G. , Jahn M. 
Published: March 2003

AbstractHigh ambient temperature (32/27 °C, day/night, 12 h photoperiod) applied prior to anthesis to Phaseolus vulgaris plants results in abnormal pollen and anther development during microsporogenesis. Scanning and transmission electron microscopy were used to examine anther and pollen morphology and pollen wall architecture after heat stress was applied to two genotypes that differ with respect to yield potential under high‐temperature field conditions: one, a heat‐sensitive, Mesoamerican genotype, A55, the second, a heat‐tolerant, Andean genotype, G122. High‐temperature treatment of both genotypes was applied 1–13 d before anthesis. Under heat stress, the heat‐tolerant genotype showed anther and pollen characteristics that were generally similar to the low temperature controls. In contrast, after 9 d of heat treatment before anthesis, the anthers of the heat‐sensitive genotype were indehiscent and contained abnormal pollen. Pollen wall architecture was also affected in the 12 and 13 d treatments. In addition to the morphological changes, the heat‐sensitive genotype also experienced reduced pollen viability and reduced yield in high‐temperature experiments conducted in both the greenhouse and field.
The effect of nitrogen and phosphorus deficiency on flavonol accumulation in plant tissues
Authors: Stewart A. J. , Chapman W. , Jenkins G. I. , Graham I. , Martin T. , Crozier A. 
Published: March 2003

AbstractThe flavonol content of Arabidopsis thaliana and tomato seedlings was assessed in conditions of reduced nitrogen or phosphorus availability. In both systems, a significant inverse relationship was observed between nutrient availability and flavonol accumulation, with nitrogen limitation promoting the greatest increase in flavonols. A trial was established to determine the effects of decreased nitrogen and phosphorus availability on the flavonol content of leaf and fruit tissues of tomato plants (Lycopersicon esculentum cv. Chaser) in a commercial situation. Nutrients were supplied by a hydroponic system with nutrient regimes designed to provide the highest and lowest nitrogen and phosphorus levels with which it is possible to support plant growth and fruit set. Fruiting was abundant and tomato fruits were harvested at mature green, breaker and red stages of ripening; leaves were also harvested from the tops of the plants. All tissues were analysed for flavonol content using reversed‐phase high‐performance liquid chromatography. Flavonol accumulation in the leaves of mature tomato plants was found to increase significantly in response to nitrogen stress, whereas phosphorus deficiency did not elicit this response. Reduced nitrogen availability had no consistent effect on the flavonol content of tomato fruits. Phosphorus deficiency elicited an increase in flavonol content in early stages of ripening. Effects of nutrient stress on the flavonol content of tomato fruits were lost as ripening progressed. The findings suggest that nutrient status may be employed to manipulate the flavonol content of vegetative tissues but cannot be used to elevate the flavonol content of tomato fruit.
Molecular and genetic aspects of plant responses to osmotic stress
Authors: Xiong L. , Zhu J.‐K. 
Published: March 2003

AbstractDrought, high salinity and freezing impose osmotic stress on plants. Plants respond to the stress in part by modulating gene expression, which eventually leads to the restoration of cellular homeostasis, detoxification of toxins and recovery of growth. The signal transduction pathways mediating these adaptations can be dissected by combining forward and reverse genetic approaches with molecular, biochemical and physiological studies. Arabidopsis is a useful genetic model system for this purpose and its relatives including the halophyte Thellungiella halophila, can serve as valuable complementary genetic model systems.
Co‐action of temperature and phosphate in inducing turion formation in Spirodela polyrhiza (Great duckweed)*
Authors: Appenroth K.‐J. 
Published: March 2003

AbstractIncreased phosphate concentration, higher temperature and addition of glucose all increased the number of fronds and turions of the duckweed Spirodela polyrhiza formed under in vitro conditions. Increasing the number of turions by increasing the plant biomass does not mean that the developmental process (switch of the programme of the primordia from vegetative fronds toward resting turions) has been specifically influenced. The specific turion yield (STY; number of turions formed by one frond) and the time of onset of turion formation have been used as more specific measures of turion induction. At more than 30 µm initial phosphate the STY was increased by lower temperature (15 °C) and became independent of the phosphate concentration. Between 10 and 30 µm and at higher temperatures (25  °C) the STY was increased by lower phosphate levels. The stimulatory effect of lower temperature was more pronounced than that of lower phosphate concentrations. Decreased phosphate concentration highly accelerated the formation of the first turions. The influence of low temperature was small at lower phosphate concentration but became dominant at higher concentrations (especially in autotrophic cultures). Low phosphate levels (e.g. 10 µm) and low temperatures (e.g. 15 °C) both represent specific turion‐inducing factors having significant interactive effects. In S. polyrhiza, these signals may replace the interactive effects of photoperiods and low temperature known from other hydrophytes in turion induction under natural conditions.
Temperature response of parameters of a biochemically based model of photosynthesis. I. Seasonal changes in mature maritime pine (Pinus pinaster Ait.)
Authors: Medlyn B. E. , Loustau D. , Delzon S. 
Published: March 2003

AbstractResponses of plant processes to temperature may vary according to the time scale on which they are measured. In this study, both short‐term and seasonal responses of photosynthesis to temperature were examined. A field study of seasonal changes in the temperature response of photosynthesis was conducted on two provenances, French and Moroccan, of mature maritime pine (Pinus pinaster Ait.). Measurements were made every 2 months over a 1‐year period and used to parameterize a mechanistic model of photosynthesis. Temperature responses of maximum Rubisco activity, Vcmax, and potential electron transport rate, Jmax, were obtained for each measurement period, as was the response of stomatal conductance, gs, to water vapour pressure deficit (VPD). Absolute values of Vcmax and Jmax at 25 °C were related to needle nitrogen content, Narea.Narea, and thus Vcmax and Jmax, were negatively correlated with the mean minimum temperature in the month preceding measurements. The ratio of Jmax : Vcmax at 25 °C varied between 1 and 1·7 but did not show any seasonal trend. Nor was there any seasonal trend in the relative temperature response of Vcmax, which had an activation energy Ha of approximately 57 kJ mol−1 throughout the experiment. The activation energy of Jmax was also close to constant throughout the experiment, averaging 39 kJ mol−1. For the French provenance, the optimal temperature of Jmax was positively correlated with the maximum temperature of the previous day, but no such correlation was found for the Moroccan provenance. The response of gs to VPD also varied seasonally, with much stronger stomatal closure in winter months. Taken together, these results implied a translational shift downwards of the photosynthetic temperature response curve with increasing Tprev, and a shift in the temperature optimum of photosynthesis of 5–10 °C between summer and winter. These results illustrate that the short‐term temperature response of photosynthesis varies significantly on a seasonal basis.
Hydraulic and photosynthetic co‐ordination in seasonally dry tropical forest trees
Authors: Brodribb T. J. , Holbrook N. M. , Gutiérrez M. V. 
Published: March 2003

AbstractIn the present study the linkage between hydraulic, photosynthetic and phenological properties of tropical dry forest trees were investigated. Seasonal patterns of stem‐specific conductivity (KSP) described from 12 species, including deciduous, brevi‐deciduous and evergreen species, indicated that only evergreen species were consistent in their response to a dry‐to‐wet season transition. In contrast, KSP in deciduous and brevi‐deciduous species encompassed a range of responses, from an insignificant increase in KSP following rains in some species, to a nine‐fold increase in others. Amongst deciduous species, the minimum KSP during the dry season ranged from 6 to 56% of wet season KSP, indicating in the latter case that a significant portion of the xylem remained functional during the dry season. In all species and all seasons, leaf‐specific stem conductivity (KL) was strongly related to the photosynthetic capacity of the supported foliage, although leaf photosynthesis became saturated in species with high KL. The strength of this correlation was surprising given that much of the whole‐plant resistance appears to be in the leaves. Hydraulic capacity, defined as the product of KL and the soil–leaf water potential difference, was strongly correlated with the photosynthetic rate of foliage in the dry season, but only weakly correlated in the wet season.
An evaluation of the evidence for, and implications of, cytoplasmic nitrate homeostasis
Authors: Siddiqi M. Y. , Glass A. D. M. 
Published: March 2003

AbstractA review of literature, reporting values of cytoplasmic/cytosolic [NO3–] in plant cells, identified two major areas of disagreement: (1) disparity in the absolute values within the same system, and (2) constancy versus variability in cytoplasmic/cytosolic [NO3–] with varying [NO3–]o.These differences are related to the techniques used by the different authors. Estimates of cytoplasmic [NO3–] by compartmental analysis and by cell fractionation were consistently higher than the estimates by NO3–selective microelectrodes and by techniques based uponin vivoandin vitronitrate reductase activity (NRA). A model recognizing more than one cytoplasmic ionic pool would satisfactorily reconcile the differences in both aspects, i.e. absolute values and constancy. Compartmental analysis and cell fractionation techniques may measure the amount of NO3–in the cytoplasm as a whole (including organelles); by contrast, NO3–selective microelectrodes and NRA estimate only the cytosolic NO3–and, hence, may result in lower estimates. Thus, variable organellar pool(s) may maintain a constant cytosolic pool as estimated by microelectrodes. However, certain observations remain at odds with the notion of a constant cytosolic [NO3–].
Induction of systemic disease resistance and pathogen defence responses in Asparagus officinalis inoculated with nonpathogenic strains of Fusarium oxysporum
Authors: He C. Y. , Hsiang T. , Wolyn D. J. 
Published: March 2003

The ability of nonpathogenic isolates of Fusarium oxysporum (npFo) to induce systemic resistance and defence responses against subsequent challenge with a pathogenic strain of F. oxysporum f. sp. asparagi (Foa) was examined in Asparagus officinalis. In a split‐root experiment, roots inoculated with npFo exhibited a hypersensitive response and those subsequently inoculated with Foa displayed resistance. Induction of systemic resistance in npFo‐treated plants led to significantly fewer necrotic lesions (P = 0·05) and reduced Foa disease severity compared with plants not treated with npFo. In hyphal‐sandwich root inoculation experiments, activities of peroxidase and phenylalanine ammonia‐lyase and lignin content were higher in npFo‐treated plants and increased more rapidly than in npFo‐untreated plants after Foa inoculation. Antifungal activity (inhibition of fungal spore germination and germ‐tube growth) from exudates of roots inoculated with Foa were observed for npFo‐treated plants but not for npFo‐untreated plants. Thus, isolates of npFo may function as inducers of systemic acquired resistance (SAR) and defence responses against Foa invasion in A. officinalis.
Plant defence reactions against fusarium wilt in chickpea induced by incompatible race 0 of Fusarium oxysporum f.sp. ciceris and nonhost isolates of F. oxysporum
Authors: Cachinero J. M. , Hervás A. , Jiménez‐Díaz R. M. , Tena M. 
Published: March 2003

Germinated seeds of ‘kabuli’ chickpea cv. ICCV 4 were inoculated with a conidial suspension of the incompatible race 0 of Fusarium oxysporum f.sp. ciceris (Foc) or of nonhost F. oxysporum resistance ‘inducers’, and 3 days later were challenged by root dip with a conidial suspension of highly virulent Foc race 5. Prior inoculation with inducers delayed the onset of symptoms and/or significantly reduced the final amount of fusarium wilt caused by race 5. However, the extent of disease suppression varied with the nature of the inducing agent; the nonhost isolates of F. oxysporum were more effective at disease suppression than the incompatible Foc race 0. Inoculation with the inducers gave rise to synthesis of maackiain and medicarpin phytoalexins in inoculated seedlings; these did not accumulate in plant tissues but were released into the inoculum suspension. Inoculation with inducers also resulted in accumulation of chitinase, β‐1,3‐glucanase and peroxidase activities in plant roots. These defence‐related responses were induced more consistently and intensely by nonhost isolates of F. oxysporum than by incompatible Foc race 0. The phytoalexins and, to a lesser extent, the antifungal hydrolases, were also induced after challenge inoculation with Foc race 5. However, in this case the defence responses were induced in both preinduced and noninduced plants infected by the pathogen. It is concluded that the suppression of fusarium wilt in this study possibly involved an inhibitory effect on the pathogen of preinduced plant defences, rather than an increase in the expression of defence mechanisms of preinduced plants following a subsequent challenge inoculation.
Specific Proliferative and Antibody Responses of Premature Infants to Intestinal Colonization with Nonpathogenic Probiotic E. coli Strain Nissle 1917
Authors: Cukrowska B. , LodÍnová‐ŽádnÍková R. , Enders C. , Sonnenborn U. , Schulze J. , Tlaskalová‐Hogenová H. 
Published: March 2003

The aim of this study was to analyze the influence of oral administration of E. coli Nissle 1917 on the systemic humoral and cellular immunity in premature infants. Thirty‐four premature infants were colonized with E. coli Nissle 1917 in a randomized, placebo‐controlled blinded clinical trial. Stool samples of infants were analyzed repeatedly for the presence of the administered strain. The proliferative response to bacterial antigens of E. coli origin was measured in whole blood of 34 colonized infants and 27 noncolonized controls. E. coli colonization induced a significant increase in the proliferation of blood cells cultivated with bacterial components of E. coli Nissle 1917 and another E. coli strain in colonized infants as compared with noncolonized controls. Significantly higher amounts of specific anti‐E. coli Nissle 1917 antibodies (Ab) of immunoglobulin (Ig)A isotype and nonspecific polyclonal IgM were found in the blood of colonized infants compared to noncolonized placebo controls. We concluded that the oral application of E. coli Nissle 1917 after birth significantly stimulates specific humoral and cellular responses and simultaneously induces nonspecific natural immunity.