bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic resonance imaging (MRI) of water during cold acclimation and freezing in winter wheat
Authors: MILLARD M. M. , VEISZ O. B. , KRIZEK D. T. , LINE M. 
Published: April 2006

ABSTRACTNuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) were used to analyse changes in the physical state of water in wheat crowns during cold acclimation and during the freezing/thawing cycle. Spectroscopically measured average spin‐spin relaxation times (T2) decreased during cold acclimation and increased when plants were grown at normal temperature. Spin‐spin relaxation images whose contrast is proportional toT2, times were calculated allowing association of water relaxation with regions of tissue in spin‐echo images during acclimation and freezing. Images taken during freezing revealed nonuniform freezing of tissue in crowns and roots. Acclimated and non‐acclimated wheat crowns were imaged during freezing and after thawing. Spin‐echo image signal intensity andT2times decreased dramatically between ‐4°C and ‐8°C as a result of a decrease in water mobility during freezing. Images collected during thawing were diffuse with less structure and relaxation times were longer, consistent with water redistribution in tissue after membrane damage.
The effect of carbon dioxide concentration on respiration of growing and mature soybean leaves
Authors: BUNCE J. A. 
Published: April 2006

ABSTRACTSoybean plants were grown continuously at 350 and 700cm3m−3 CO2 at constant temperature. Respiration rates of third trifoliolate leaves were measured at the growth CO2 concentration for the whole dark period from 5d before through to 5d after full area expansion. The short‐term response of respiration rate to the measurement CO2 concentration was also determined at each age. Respiration rates per unit of dry mass declined with age and were significantly less at a given age or RGR in leaves grown and measured at the elevated CO2. The difference in respiration rate was largest in mature leaves and resulted from the different measurement CO2 concentrations. The respiratory costs of the tissue synthesis, estimated from the elemental composition of the tissue, did not differ substantially between CO2 treatments. The response of respiration rate to carbon dioxide concentration was not strongly affected by the form of nitrogen supplied. Maintenance respiration calculated by subtracting growth respiration from total respiration was negative in rapidly growing leaves for both CO2 treatments. This indicates that CO2 efflux in the dark does not accurately reflect the average 24 h rate of energy expenditure on growth and maintenance for soybean leaves.
Utilization of adenine and guanine as nitrogen sources by Chlamydomonas reinhardtii cells
Authors: LISA T. A. , PIEDRAS P. , CÁRDENAS J. , PINEDA M. 
Published: April 2006

ABSTRACT Chlamydomonas reinhardtü Dangeard, adenine or guanine can be used as the sole nitrogen source for growth by means of an inducible system which is repressed by ammonia. Cells grown on either adenine or guanine were able to take up both purines, although the adenine uptake rate was always about 40% of the guanine uptake rate. Both adenine and guanine were taken up by an inducible system(s) exhibiting hyperbolic kinetics with identical apparent A, values of 3‐2 mmol m−3 for adenine and 3‐2mmol m−3 for guanine. Adenine and guanine utilization depended on pH, with similar optimal pH values of 7·3 and 7·4, respectively. Adenine and guanine each acted as a competitive inhibitor of the other's uptake, and their utilization was also inhibited by hypoxanthine, xanthine and urate. Inhibition of adenine uptake by guanine and hypoxanthine was competitive, with A′, values of 5·5 and 1. 6 mmol m−3 respectively. Guanine uptake was also inhibited competitively by adenine (K1= 1·3mmol m−3) and hypoxanthine (K1= 3. 3 mmol m−3). Utilization of both adenine and guanine was inhibited by cyanide, azide, 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyl urea, 2,4‐dinitrophenol and carbonylcyanide m‐chlorophenylhydrazone, and was also sensitive to p‐hydroxymercuribenzoate and N‐ethyl‐maleimide. On the basis of these results, taken together, the possibility that adenine and guanine are translocated into Chlamydomonas by a common system is discussed.
CO2 responsiveness of plants: a possible link to phloem loading
Authors: KÖRNER CH. , PELAEZ‐RIEDL S. , VAN BEL A. J. E. 
Published: April 2006

ABSTRACTOf the many responses of plants to elevated CO2, accumulation of total non‐structural carbohydrates (TNC in % dry weight) in leaves is one of the most consistent. Insufficient sink activity or transport capacity may explain this obvious disparity between CO2 assimilation and carbohydrate dissipation and structural investment. If transport capacity contributes to the problem, phloem loading may be the crucial step. It has been hypothesized that symplastic phloem loading is less efficient than apoplastic phloem loading, and hence plant species using the symplastic pathway and growing under high light and good water supply should accumulate more TNC at any given CO2 level, but particularly under elevated CO2. We tested this hypothesis by carrying out CO2 enrichment experiments with 28 plant species known to belong to groups of contrasting phloem‐loading type. Under current ambient CO2 symplastic loaders were found to accumulate 36% TNC compared with only 19% in apoplastic loaders (P=0.0016). CO2 enrichment to 600 μmol mol−1 increased TNC in both groups by the same absolute amount, bringing the mean TNC level to 41% in symplastic loaders (compared to 25% in apoplastic loaders), which may be close to TNC saturation (coupled with chlornplast malfunction). Eight tree species, ranked as symplastic loaders by their minor vein companion cell configuration, showed TNC responses more similar to those of apoplastic herbaceous loaders. Similar results are obtained when TNC is expressed on a unit leaf area basis, since mean specific leaf areas of groups were not significantly different. We conclude that phloem loading has a surprisingly strong effect on leaf tissue composition, and thus may translate into alterations of food webs and ecosystem functioning, particularly under high CO2.
A model of the acclimation of photosynthesis in the leaves of C3 plants to sun and shade with respect to nitrogen use
Authors: HIKOSAKA K. , TERASHIMA I. 
Published: April 2006

ABSTRACTA model of leaf photosynthesis of C3, plants has been developed to describe their nitrogen economy. In this model, photosynthetic proteins are categorized into five groups depending on their functions. The effects of investment of nitrogen in each of these groups on the maximal rate of photosynthesis and/or the initial slope of the light‐response curve are described as simple equations. Using this model, the optimal pattern of nitrogen partitioning which maximizes the daily rate of CO2 exchange is estimated for various light environments and leaf nitrogen contents. When the leaf nitrogen content is fixed, the amount of nitrogen allocated to Calvin cycle enzymes and electron carriers increases with increasing irradiance, while that allocated to chlorophyll‐protein complexes increases with decreasing irradiance. For chlorophyll‐proteins of photosystem II, the amount of light‐harvesting complex II relative to that of the core complex increases with decreasing irradiance. At any irradiance, partitioning into ribulose bisphosphate carboxylase increases with increasing leaf nitrogen content Taking the total leaf nitrogen content and the daily CO2 exchange rate as ‘cost’ and ‘benefit’, respectively, the optimal amount and partitioning of nitrogen are examined for various conditions of light environment and nitrogen availability. The leaf nitrogen content that maximizes the rate of daily carbon fixation increases with increasing growth irradiance. It is also predicted that, at low nitrogen availabilities, low leaf nitrogen contents are advantageous in terms, of nitrogen use efficiency. These trends predicted by the present model are largely consistent with those reported for actual plants. The differences in the total amount of leaf nitrogen and in the organization of photosynthetic components that have been reported for plants from different environments would therefore be of adaptive significance, because such differences can contribute to realization of efficient photosynthesis. These results are fürther discussed in an ecological context.
In situ estimation of net CO2 assimilation, photosynthetic electron flow and photorespiration in Turkey oak (Q. cerris L.) leaves: diurnal cycles under different levels of water supply
Authors: VALENTINI R. , EPRON D. , DE ANGELIS P. , MATTEUCCI G. , DREYER E. 
Published: April 2006

ABSTRACTDiurnal time courses of net CO2 assimilation rates, stomatal conductance and light‐driven electron fluxes were measured in situ on attached leaves of 30‐year‐old Turkey oak trees (Quercus cerris L.) under natural summer conditions in central Italy. Combined measurements of gas exchange and chlorophyll a fluorescence under low O2 concentrations allowed the demonstration of a linear relationship between the photochemical efficiency of PSII (fluorescence measurements) and the apparent quantum yield of gross photosynthesis (gas exchange). This relationship was used under normal O2 to compute total light‐driven electron fluxes, and to partition them into fractions used for RuBP carboxylation or RuBP oxygenation. This procedure also yielded an indirect estimate of the rate of photorespiration in vivo. The time courses of light‐driven electron flow, net CO2 assimilation and photorespiration paralleled that of photosynthetic photon flux density, with important afternoon deviations as soon as a severe drought stress occurred, whereas photochemical efficiency and maximal fluorescence underwent large but reversible diurnal decreases. The latter observation indicated the occurrence of a large non‐photochemical energy dissipation at PSII. We estimated that less than 60% of the total photosynthetic electron flow was used for carbon assimilation at midday, while about 40% was devoted to photorespiration. The rate of carbon loss by photorespiration (R1) reached mean levels of 56% of net assimilation rates. The potential application of this technique to analysis of the relative contributions of thermal de‐excitation at PSII and photorespiratory carbon recycling in the protection of photosynthesis against stress effects is discussed.
Can perennial C4 grasses attain high efficiencies of radiant energy conversion in cool climates?
Authors: BEALE C. V. , LONG S. P. 
Published: April 2006

ABSTRACTAlthough C4 plants are considered to have higher conversion efficiency and productivity than C3, plants, this advantage may not be realized under sub‐optimal conditions. Two perennial C4 rhizomatous grasses of cool temperate origin, Miscanthus × giganteus and Spartina cyno‐suroides, have been suggested as potential fuel crops for north‐western Europe. The conversion efficiencies of these species were examined for 2 years in fertilized, irrigated, replicated plots in south‐eastern England. In the second year, the energy conversion efficiencies for shoot and total biomass production were 0.040 and 0.051, respectively, for S. cynosuroides, with significantly higher values of 0.060 and 0.078, respectively, for M. × giganteus. The M. × giganteus crop attained shoot productivity of 2.87 kg m−2 between April and September, exceeding the highest values typically obtained with intensively managed C3, crops. Canopy development was early, and high interception and conversion efficiencies were maintained over most of the growing season. This study provides the evidence that the superior potential light conversion efficiencies associated with C4 photosynthesis can be realized under cool temperate conditions and that such climatic conditions do not Inherently impair the C4 process.
Evidence that the partial resistance of theArabidopsis 5‐2mutant to fusicoccin depends on a decreased capacity of the H+pump to respond to activating factors
Authors: MARRÉ M. T. , VENEGONI A. , TALARICO A. , SOAVE C. , MARRÉ E. 
Published: April 2006

ABSTRACTMeasurements of H+extrusion activity K+influx, andEs bm in 3‐d‐old seedlings of the 5‐2 mutant ofArabidopsis thaliana(which is partially insensitive to fusicoccin) showed the following, (i) The reduced response of5‐2to fusicoccin (FC) does not depend on the penetration of FC to its site of action, or on decreased affinity of the FC receptor, (ii) The reduced response of H+and K+transport to FC does not depend on an impairment of the K+absorption system, (iii) The mutation can influence the H+extrusion system independently of the presence of FC. In the presence of factors other than FC known to activate the plasma membrane H+‐ATPase (e.g. a cytosol‐acidifying treatment), the response in 5‐2 is about 50% lower than inwt.(iv) When both genotypes grow in optimal conditions, the rate of fresh weight increase and stem elongation is higher inwtthan5‐2. These data indicate that the5‐2mutation affects some intrinsic component of the H+‐extrusion machinery, the limiting effect of which becomes considerable when either the physiological or the experimental conditions induce a high level of proton pump activity. An alteration either of the ATPase itself or of a factor controlling its activity is compatible with our observations.
Base and optimum temperatures vary with genotype and stage of development in wheat
Authors: SLAFER G. A. , RAWSON H. M. 
Published: April 2006

ABSTRACTSome assumptions concerning development in wheat (Triticum aestivum, L.) were examined. These are that (i) the rate of development towards anthesis increases linearly with temperature, (ii) the base temperature is 0°C, (iii) the optimum temperature is above the range at which wheat is normally grown, (iv) base and optimum temperatures do not change with development, and (v) the relationships for different cultivars are similar. We tested these assumptions in studies using a naturally lit phytotron with four cultivars and six temperature regimes between 10 and 25°C. Seedlings were vernalized for 50 d and then grown under a photoperiod of 18 h to avoid confounding the responses to vernalization and photoperiod with those to temperature. In cultivars Sunset and Rosella, the rate of development for the full period to anthesis increased linearly between base and optimum temperatures. However, in cultivars Condor and Cappelle Desprez, a linear fit was not statistically acceptable. For these cultivars, the rate of development towards anthesis increased rapidly with increase in temperature from 10 to 19°C, but temperatures higher than 19°C had little or no fürther accelerating effect. When a linear relationship was fitted by ignoring data for temperatures above 19 7deg;C, base temperatures calculated for the full period to anthesis were c. 5.5, 5.5,4.0 and 2.5°C for Sunset, Condor, Rosella and Cappelle Desprez, respectively (i.e. an average value of c. 4 7deg;C). The full period to anthesis was subdivided into three phases for fürther analysis. These were (i) from the beginning of the experiment to terminal spikelet initiation, (ii) from terminal spikelet initiation to heading, and (iii) from heading to anthesis. When these sub‐phases were analysed a linear relationship was found to be appropriate for all combinations of cultivar and developmental phase. However, both base and optimum temperatures calculated from the relationships increased as development progressed from (i) to (iii). Averaging across cultivars, base temperatures for the three phases were ‐1.9, %1.2 and %8.1°C, respectively, while optimum temperatures were <22, 25 and >25°C, respectively. Cultivars differed substantially in all these parameters. The progressive increase in optimum temperature with phasic development was apparently the main reason why linear fits for the three sub‐phases became a curvilinear fit for the full phase to anthesis.
The expression of cellulase gene family members during induced avocado fruit abscission and ripening
Authors: TONUTTI P. , CASS L. G. , CHRISTOFFERSEN R. E. 
Published: April 2006

ABSTRACTThe expression of specific cellulase (endo‐l,4‐β‐glucanase; EC 3‐2‐1‐4) gene family members was monitored in the mesocarp and abscission zone of mature avocado fruit. Fruit abscission was induced by either girdling of the stem or treatment with 2‐chloroethyl phosphonic acid (CEPA). Gene‐specific probes that hybridized to the 3′ untranslated region of either the cel1 or the cel2 gene of avocado were used to distinguish between RNA transcripts from these two closely related genes. Only cel1 transcripts were detected in ripe mesocarp. An accumulation of cel1 mRNA has been observed in the activated fruit abscission zone. Using antibody raised against cellulase protein isolated from ripe fruit, a cross‐reacting cellulase antigen was detected in extracts from the abscission zones of CEPA‐treated and girdled fruit. Cellulase enzyme activity was detected in these tissues. These results suggest that the same cellulase gene (cel1) that has been shown to be expressed in the mesocarp during fruit ripening might also be involved in the mature fruit abscission process.
Microaerobic respiration and oxidative phosphorylation by soybean nodule mitochondria: implications for nitrogen fixation
Authors: MILLAR A. H. , DAY D. A. , BERGERSEN F. J. 
Published: April 2006

ABSTRACTThe infected cells of soybean (Glycine max) root nodules require ATP production for ammonia assimilation and purine synthesis under microaerobic conditions. It is likely that the bulk of this demand is supplied through mitochondrial oxidative phosphorylation. Mitochondria purified from root nodules respired and synthesized ATP in sub‐micromolar oxygen concentrations as measured by leghaemoglobin spectroscopy and luciferase luminescence. Both oxygen uptake and the apparent ATP/O ratio declined significantly as the oxygen concentration fell below 100 μmol m−3. Cytochrome‐pathway respiration by root nodule mitochondria had a higher apparent affinity for oxygen (Km 50 μmol m−3) than did mitochondria isolated from roots (Km 125 μmol m−3). Electron micrographs showed that mitochondria predominated at the periphery of infected cells adjacent to gas‐filled intercellular spaces, where the oxygen concentration is predicted to be highest. Calculations of oxygen concentration and nitrogen fixation rates on an infected cell basis suggest that the measured rates of ATP production by isolated mitochondria are sufficient for the quantifiable in vivo requirements of ammonia assimilation and purine synthesis. The possible roles of mitochondrial respiration in the control of infected cell metabolism are also discussed.
Effects of elevated CO2 concentration and increased temperature on winter wheat: test of ARCWHEAT1 simulation model
Authors: MITCHELL R.A.C. , LAWLOR D.W. , MITCHELL V.J. , GIBBARD C.L. , WHITE E.M. , PORTER J.R. 
Published: April 2006

ABSTRACTWinter wheat (Triticum aestivum L., ev. Mercia) was grown in a controlled‐environment facility at two CO2 concentrations (targets 350 and 700 μmol mol−1), and two temperature regimes (tracking ambient and ambient + 4°C). Observations of phenology, canopy growth, dry matter production and grain yield were used to test the ARCWHEAT1 simulation model. Dry‐matter production and grain yield were increased at elevated CO2 concentration (27 and 39%, respectively) and reduced at increased temperature (−16 and −35%, respectively). ARCWHEAT1 substantially underestimated canopy growth for all treatments. However, differences in the facility environment from field conditions over the winter, indicated by the unusually rapid canopy growth observed in this period, meant that empirical model relationships were being used outside the conditions for which they were developed. The ARCWHEAT productivity submodel, given observed green area indices as inputs, overestimated the effect of CO2 on productivity. An alternative, more mechanistic submodel of productivity, based on the SUCROS87 and Farquhar & von Caemmerer models, simulated observed crop biomass very closely. When these productivity simulations were inputed into the ARCWHEAT1 partitioning and grain‐fill submodels, grain yield was predicted poorly, mainly as a result of the assumption that the number of grains is proportional to total growth during a short pre‐anthesis phase. While yield was not correlated with growth in this phase, it was correlated with growth in longer pre‐anthesis phases, indicating that ARCWHEAT1 could be improved by taking into account the contribution of earlier growth in determining yield.
Changes in trace metal species and other components of the rhizosphere during growth of radish
Authors: HAMON R. E. , LORENZ S. E. , HOLM P. E. , CHRISTENSEN T. H. , McGRATH S. P. 
Published: April 2006

ABSTRACTChanges in the properties of soil solution in the rhizosphere of developing radish plants were investigated. Variations in these properties were expected to affect the distribution and speciation of metals in the soil and soil solution. Applications of essential nutrients were linked to plant transpiration rates and prevented excess addition of nutrient ions, so that subtle changes in soil solution composition would not be obscured. Soil solution pH, the concentration of dissolved organic carbon (DOC) and the concentrations of major and trace elements in solution were found to vary over time. Strict control of fertilizer additions led to the maintenance of a relatively low ionic strength in the soil solution, and under such conditions trace metal solubility appeared to be highy influenced by the concentration of DOC. A chemical speciation analysis was performed which showed that, while dissolved Cd and Zn were largely uncomplexed in unplanted soil, Cd and Zn in the rhizosphere existed mainly as complexed forms. It is hypothesized that this is partly a result of Ca‐metal‐ligand equilibrium in solution, with higher Ca concentrations in unplanted soil leading to more of the Cd and Zn in solution existing in the uncomplexed state. Changes in the concentrations of uncomplexed Cd and Zn with time gave the best correlations with changes in plant uptake of these metals over time, supporting the hypothesis that plants mainly absorb the free metal ion from soil solution.
Effects of nitrogen limitation on water relations of jack pine (Pinus banksiana Lamb.) seedlings
Authors: TAN W. , HOGAN G. D. 
Published: April 2006

ABSTRACTThe water relations of shoots of young jack pine (Pinus banksiana Lamb.) seedlings were examined 6 and 15 weeks after the initiation of four different dynamic nitrogen (N) treatments using a pressure‐volume analysis. The N treatments produced a wide range of needle N concentrations from 12 to 32 mg g−1 dry mass and a 10‐fold difference in total dry mass at 15 weeks. Osmotic potential at full turgor did not change over the range of needle N concentrations observed. Osmotic potential at turgor‐loss point, however, declined as N concentrations decreased, indicating an increased ability of N‐deficient jack pine plants to maintain turgor. The increase could be attributed largely to an increase in cell wall elasticity, suggesting that elasticity changes may be a common, significant adaptation of plants to environmental stresses. Dry mass per unit saturated water almost doubled as needle N level dropped from 32 to 12 mg g−1 and was inversely correlated to the bulk modulus of elasticity. This suggests that cell wall elasticity is determined more by the nature of its cross‐linking matrix than by the total amount of cell wall material present. Developmental change was evident in the response of some water relation variables to N limitation.