bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of phosphoeno/pyruvate carboxylase (PEPCase) in Mesembryanthemum crystallinum L. in C3 and CAM photosynthetic states
Authors: SLOCOMBE S. P. , WHITELAM G. C. , COCKBURN W. 
Published: April 2006

ABSTRACTWhen exposed to osmotic stress, Mesembryanthemum crystallinum plants switch from C3 to CAM photosynthesis. Phosphoenolpyruvate carboxylase (PEPCase) is a key enzyme in CAM plants, being responsible for the initial fixation of CO2. In C3 plants the enzyme has been shown to be involved in the replenishing of TCA cycle intermediates and in the operation of stomatal guard cells. Multiple PEPCase isoforms were observed in C3‐performing leaves with four isoelectric points of 5.2, 5.5, 5.6 and 5.9 and four apparent subunit molecular masses of 105, 108, 113 and 116 kDa. In some instances, subunits of different size possessed exactly the same pI. The induction of CAM led to the predominance of a new isoform of pI 6.5 with subunit molecular mass of 108 kDa, but in addition, changes were observed in some of the isoforms present in the C3 plant. PEPCase subunits were purified from the C3 and CAM forms of M. crystallinum and subjected to pep‐tide mapping. Two distinct though similar sets of maps were obtained, one from the CAM isoform (pI 6.5) and C3‐associated subunits of pi 5.9 and another for C3 subunits of pI 5.2 and 5.5. It was inferred from these data that the C3 isoforms expressed in the leaf were derived from at least two genes. The C3 isoform (pI 5.9) showing greatest similarity to the CAM isoform in terms of peptide mapping also increased in response to salt stress. It is speculated that the CAM isoform may have evolved from this enzyme.
Degradation of proteins from thylakoid membranes in senescing wheat leaves at high temperature
Authors: FERGUSON* D. L. , AL‐KHATIB K. , GUIKEMA J. A. , PAULSEN G. M. 
Published: April 2006

ABSTRACTThis investigation determined whether thylakoid proteins would be degraded more rapidly or not in senescing wheat (Triticum aestivum L. em. Thell.) leaves concurrently exposed to high temperatures. Excised leaves were pulse‐labelled with [35S]‐methionine for a 12 h period, and then incubated at 22,32 or 42°C for 0, 1, 2, or 3 d, before extracting a thylakoid enriched membrane sample. After electrophoretic separation, two prominent [35S]‐labelled protein bands were chosen for further analyses. Band A contained the D‐1 thylakoid protein and band B contained thylakoid proteins of the light harvesting complex (LHCII) associated with photosystem II (PSII). Total protein, [35S]‐labelled protein, band A protein, and band B protein within the thylakoid enriched membrane samples were measured. Unlabelled thylakoid enriched membrane samples, extracted from leaves given similar treatments, were used to measure uncoupled whole‐chain and photosystem II (PSII) electron transport and chlorophyll fluorescence. Accentuated decline in whole‐chain and PSII electron transport, increasing Fo values, and decreasing Fmax values were a result of high temperature injury in leaves treated at 42°C. None of the thylakoid enriched membrane protein fractions were degraded more rapidly in high‐temperature treated leaves. Degradation of the total [35S]‐labelled membrane proteins and band B was inhibited by the 42°C treatment. The results indicate that high temperature stress may disrupt some aspects of normal senescence.
Different vulnerabilities of Quercus ilex L. to freeze‐ and summer drought‐induced xylem embolism: an ecological interpretation
Authors: LO GULLO M. A. , SALLEO S. 
Published: April 2006

ABSTRACT Quercus ilex L. growing in the southern Mediterranean Basin region is exposed to xylem embolism induced by both winter freezing and summer drought. The distribution of the species in Sicily could be explained in terms of the different vulnerability to embolism of its xylem conduits. Naturally occurring climatic conditions were simulated by: (1) maintaining plants for 3h at ambient temperatures of 0, ‐1.5, ‐2.5, ‐5.0 and ‐11°C; and (2) allowing plants to dry out to ratios of their minimum diurnal leaf water potentials (Ψ1) to that at the turgor loss point (Ψtlp) of 0.6, 0.9, 1.05, 1.20 and 1.33. The loss of hydraulic conductivity of one‐year‐old twigs reached 40% at ‐1.5°C and at Ψ1/ΨtlP= 1.05. Recovery from these strains was almost complete 24 h after the release of thermal stress or after one irrigation, respectively. More severe stresses reduced recovery consistently. The percentages of xylem conduits embolized following application of the two stresses, were positively related to xylem conduit diameter. The capability of the xylem conduits to recover from stress was positively related to the conduit diameter in plants subjected to summer drought, but not in the plants subjected to winter freezing stress. The ecological significance of the different vulnerabilities to embolism of xylem conduits under naturally occurring climatic conditions is discussed.
Effects of increased CO2 concentration and temperature on growth and yield of winter wheat at two levels of nitrogen application
Authors: MITCHELL R. A. C. , MITCHELL V. J. , DRISCOLL S. P. , FRANKLIN J. , LAWLOR D. W. 
Published: April 2006

ABSTRACTWinter wheat (Triticum aestivum L., cv. Mercia) was grown in chambers under light and temperature conditions similar to the UK field environment for the 1990/1991 growing season at two levels each of atmospheric CO2 concentration (seasonal means: 361 and 692 μmol mol−1), temperature (tracking ambient and ambient +4°C) and nitrogen application (equivalent to 87 and 489 kg ha−1 total N applied). Total dry matter productivity through the season, the maximum number of shoots and final ear number were stimulated by CO2 enrichment at both levels of the temperature and N treatments. At high N, there was a CO2‐induced stimulation of grain yield (+15%) similar to that for total crop dry mass (+12%), and there was no significant interaction with temperature. This contrasts with other studies, where positive interactions between the effects of increases in temperature and CO2 have been found. Temperature had a direct, negative effect on yield at both levels of the N and CO2 treatments. This could be explained by the temperature‐dependent shortening of the phenological stages, and therefore, the time available for accumulating resources for grain formation. At high N, there was also a reduction in grain set at ambient +4°C temperature, but the overall negative effect of warmer temperature was greater on the number of grains (‐37%) than on yield (‐18%), due to a compensating increase in average grain mass. At low N, despite increasing total crop dry mass and the number of ears, elevated CO2 did not increase grain yield and caused a significant decrease under ambient temperature conditions. This can be explained in terms of a stimulation of early vegetative growth by CO2 enrichment leading to a reduction in the amount of N available later for the formation and filling of grain.
Growth and maintenance components of leaf respiration of cotton grown in elevated carbon dioxide partial pressure
Authors: THOMAS R. B. , REID C. D. , YBEMA R. , STRAIN B. R. 
Published: April 2006

ABSTRACTElevated atmospheric carbon dioxide partial pressures have been shown to have variable direct and indirect effects on plant respiration rates. In this study, growth, leaf respiration, and leaf nitrogen and carbohydrate partitioning were measured in Gossypium hirsutum L. grown in 35 and 65 Pa CO2 for 30d. Growth and maintenance coefficients of leaf respiration were estimated using gas exchange techniques both at night and during the day. Elevated CO2 stimulated biomass production (107%) and net photo‐synthetic rates (35–50%). Total day‐time respiration (Rd) was not significantly affected by growth CO2 partial pressure. However, night respiration (Rn) of leaves grown in 65 Pa CO2 was significantly greater than that of plants grown in 35 Pa CO2. Correlation of Rd and Rn with leaf expansion rates indicated that plants in both CO2 treatments had equivalent growth respiration coefficients but maintenance respiration was significantly greater in elevated CO2. Increased maintenance coefficients in elevated CO2 appeared to be related to increased starch accumulation rather than to changes in leaf nitrogen.
Isoprene emission by plants is affected by transmissible wound signals
Authors: LORETO F. , SHARKEY T. D. 
Published: April 2006

ABSTRACTIsoprene (2‐methyl 1,3‐butadiene) is emitted from many plants, but the signals regulating isoprene emission are unknown. Mounting leaves in a gas exchange chamber or taking small leaf punches for biochemical analysis was found to reduce the rate of isoprene emission (Loreto & Sharkey 1993). This phenomenon was investigated by putting terminal leaflets of velvet bean (Mucuna deeringeniana L.) and kudzu [Pueraria lobaia (Willd) Ohwi.] into a gas exchange chamber and monitoring isoprene emission and photosynthesis. Lateral leaflets or remote leaves were then wounded or mechanically stimulated. The rate of isoprene emission was reduced after 1 min by up to 75% by burning a lateral leaflet with a match. Even a 7 ms−1 (25km h−1) wind imposed on a lateral leaflet reduced isoprene emission from the terminal leaflet by 18%. Photosynthesis rates were either unaffected by these treatments or reduced more slowly than isoprene emission rates, indicating that the effect of isoprene emission rates was not a consequence of changes in photosynthetic activity. Isoprene emission from a terminal leaflet was reduced by burning leaves above and below the monitored leaflet when on the same stem. The effect was much reduced if the burned leaf (all three leaflets) was on a different stem from the monitored leaflet. Reduction of the rate of isoprene emission was observed even when the burned leaf was 52 cm distant from the measured leaflet. Increasing the distance between the stressed leaf and the monitored leaf caused the effect to be slower and smaller. It is speculated that a signal is generated by wounding which propagates through the plant at 1.3 mm s−1. This velocity was consistent throughout the measurements and is similar to the rate of propagation of electrical signals such as action potentials and variation potentials. The effect of the environmental stress, and particularly the wind effect, can be frequent in nature and should be considered when estimating local and regional emission of isoprene for modelling atmospheric chemistry. If leaf samples used for isoprene determination are exposed to the type of stress we investigated, isoprene emission inventories based on leaf level measurements will be underestimated.
Facility for studying the effects of elevated carbon dioxide concentration and increased temperature on crops
Authors: LAWLOR D. W. , MITCHELL R. A. C. , FRANKLIN J. , MITCHELL V. J. , DRISCOLL S. P. , DELGADO E. 
Published: April 2006

ABSTRACTThe requirements for the experimental study of the effects of global climate change conditions on plants are outlined. A semi‐controlled plant growth facility is described which allows the study of elevated CO2 and temperature, and their interaction on the growth of plants under radiation and temperature conditions similar to the field. During an experiment on winter wheat (cv. Mercia), which ran from December 1990 through to August 1991, the facility maintained mean daytime CO2 concentrations of 363 and 692 cm3 m−3 for targets of 350 and 700 cm3 m−3 respectively. Temperatures were set to follow outside ambient or outside ambient +4°C, and hourly means were within 0.5°C of the target for 92% of the time for target temperatures greater than 6°C. Total photosynthetically active radiation incident on the crop (solar radiation supplemented by artifieal light with natural photoperiod) was 2% greater than the total measured outside over the same period.
Genetic approaches to auxin action
Authors: HOBBIE L. , ESTELLE M. 
Published: April 2006

ABSTRACTAnswers to long‐standing questions concerning the molecular mechanism of auxin action and auxin's exact functions in plant growth and development are beginning to be uncovered through studies using mutant and transgenic plants. We review recent work in this area in vascular plants. A number of conclusions can be drawn from these studies. First, auxin appears essential for cell division and viability, as auxin auxotrophs isolated in tissue culture are dependent on auxin for growth and cannot be regenerated into plants even when auxin is supplied exogenously. Secondly, plants with transgenes that alter auxin levels are able to regulate cellular auxin concentrations by synthesis and conjugation; wild‐type plants are probably also capable of such regulation. Thirdly, the phenotypes of transgenic plants with altered auxin levels and of mutant plants with altered sensitivity to auxin confirm earlier physiological studies which indicated a role for auxin in regulation of apical dominance, in development of roots and vascular tissue, and in the gravitropic response. Finally, the cloning of a mutationally identified gene important for auxin action, along with accumulating biochemical evidence, hints at a major role for protein degradation in the auxin response pathway.
Metabolic control analysis of plant metabolism
Authors: Ap REES T. , HILL S. A. 
Published: April 2006

ABSTRACTMetabolic control analysis and its major coefficients are introduced. The importance of measuring both elasticity and concentration‐control coefficients as well as flux‐control coefficients is stressed. The conditions that need to be met before control analysis can be applied experimentally are emphasized. It is argued that successful application of this approach requires methods for the measurement of flux, maximum catalytic activities of enzymes and substrate contents. The measurement of flux by consumption of substrate, production of product, and the distribution of isotope after metabolism of labelled substrates is discussed. The need to ensure that measurements of enzymes and substrates are reliable and authenticated is stressed. Particular emphasis is placed on the ease with which such measurements can be invalidated in plant tissues, and ways for countering these difficulties are discussed.
Use of transgenic plants and mutants to study the regulation and function of lipid composition
Authors: GIBSON S. , FALCONE D. L. , BROWSE J. , SOMERVILLE C. 
Published: April 2006

ABSTRACTMutants and transgenic plants with altered expression of genes implicated in lipid metabolism are providing fresh insights into the regulation and function of lipid composition. To date, several genes encoding fatty acid desaturases, acyltransferases, a thioesterase, a lipid transfer protein and an isoform of acyl‐carrier protein have been introduced into transgenic plants. Despite the fact that some of these transgenic plants had large alterations in lipid composition, they showed surprisingly little phenotypic variation from wild‐type plants. Although detailed analyses of these plants are just beginning, several theories regarding the roles of particular genes in various plant processes, such as cold tolerance and transfer of lipids between membranes, have been either substantiated or discarded on the basis of the data already obtained. In addition, constructs that contain the promoter regions of genes implicated in lipid metabolism fused to reporter genes have been introduced into transgenic plants and are providing some clues as to how lipid composition is regulated.
Mutational analysis of blue‐light sensing in Arabidopsis
Authors: LISCUM E. , HANGARTER R. P. 
Published: April 2006

ABSTRACTBlue light regulates many physiological and developmental processes in higher plants through the action of multiple photosensory systems. The analysis of photomorphogenic mutants is leading to a better understanding of how the different photosensory systems mediate the wide range of responses observed in blue light. A review of the current literature on photomorphogenic mutants makes it apparent that redundancies exist in photoreceptor function. For example, many blue‐light responses that have been shown to be regulated by a blue‐light photosensory system are also under phytochrome control. The study of various light‐response mutants suggests that a complex sensory network regulates light‐mediated responses. This article attempts to piece together information regarding the sensory systems responsible for blue‐light‐regulated responses.
Manipulation of sink‐source relations in transgenic plants
Authors: SONNEWALD U. , LERCHL J. , ZRENNER R. , FROMMER W. 
Published: April 2006

ABSTRACTSince 1980, the use of transgenic plants in modern plant science has become a powerful tool to study whole plant physiology. In this review, we try to summarize the data obtained in the field of photoassimilate partitioning. Attempts to study sink‐source interactions concern factors which might limit sink strength and source capacity. Transgenic plants have been used to manipulate the sucrose to starch ratio in order to produce plants with higher sucrose levels in their source leaves. Alterations in partitioning were achieved by manipulating Calvin cycle enzymes, transport proteins and sucrose biosynthetic enzymes. The ability of sink tissues to attract photoassimilates has been altered by either increasing or decreasing sucrose hydrolytic activities. The increase of sucrose hydrolysis was achieved by creating transgenic potato plants with tuber specific yeast‐derived invertase. Decreased sucrose utilization was achieved by antisense inhibition of sucrose synthase in potato tubers.
Insights into root development from Arabidopsis root mutants
Authors: BENFEY P. N. , SCHIEFELBEIN J. W. 
Published: April 2006

ABSTRACTThe root provides a useful system for the analysis of plant organ formation. Mutations that affect root development and physiology have been identified in Arabidopsis thaliana. Affected processes include embryonic root formation, cell expansion, cell differentiation and response to environmental stimuli. Analysis of these mutations is providing insight into fundamental questions of plant development.
Phenotypic plasticity of stem elongation in two ecotypes of Stellaria longipes: the role of ethylene and response to wind
Authors: EMERY R. J. N. , REID D. M. , CHINNAPPA C. C. 
Published: April 2006

ABSTRACTUsing two ecotypes of Stellaria longipes an alpine form with low plasticity and a prairie form with high plasticity, we investigated whether ethylene was involved in the response to wind stress and might be important in controlling plasticity of stem elongation. Stem growth inhibition was positively correlated with concentration of ethephon application and elevation in ambient ethylene in alpine ecotypes, whereas stem growth in prairie plants was stimulated by low ethephon concentrations. When treated with high AVG, the effects were reversed: alpine plant growth was promoted and prairie plant growth was inhibited. Prairie plants exhibited a daily rhythm in ethylene evolution which increased and peaked at 1500 h, and which was absent in alpine plants. Ethylene evolution did not change significantly during the first 2 weeks of growth in alpine plants, whereas ethylene in prairie plants increased significantly during periods of rapid stem elongation. Wind treatment inhibited growth in both ecotypes, but only alpine plants showed a recovery of growth to control levels when wind stressed plants were pretreated with STS. In addition, only alpine plants showed an increase in ethylene evolution in response to wind simulation, whereas prairie plant ethylene evolution did not deviate from rhythms observed in unstressed plants. We concluded that ethylene dwarfs stems in alpine S. longipes in response to wind stress. However, low levels of ethylene may stimulate growth in prairie ecotypes and act independently of wind stress intensity. The contrasting ability to synthesize and respond to ethylene can account for part of the difference in plasticity documented between the two ecotypes.
How much sodium accumulation is necessary for salt tolerance in subspecies of the halophyte Atriplex canescens?
Authors: GLENN E. P. , OLSEN M. , FRYE R. , MOORE D. , MIYAMOTO S. 
Published: April 2006

ABSTRACTTwo sympatric subspecies of the xerohalophyte Atriplex canescens Pursh. (Nutt.) were compared for 84 d in outdoor salinity trials in their native coastal desert environment in Sonora, Mexico. Subspecies linearis grows naturally on sea water in the high intertidal zone of estuaries while subspecies canescens grows on dunes. In lysimeter pot experiments, ssp. linearis exhibited 50% growth reduction when the mean root zone salinity reached 1160 mol m−3 NaCl compared to just 760 mol m−3 for ssp. canescens. When irrigated with sea water in a flood plot, ssp. linearis had 50% higher growth rates than ssp. canescens. The specialization of ssp. linearis for a saline environment was associated with greater net transport of Na+ from root to shoot, greater Na+ accumulation in the leaves and a higher Na:K ratio in the leaves compared to ssp. canescens. On the other hand, the two subspecies achieved approximately the same degree of osmotic adjustment in the leaves, equal to two to three times the external salinity, and had similar water use efficiencies. Even at relatively low salinities, both subspecies accumulated larger quantities of Na+ for osmotic adjustment than K+. The results suggest that breeding for Na+ accumulation rather than exclusion might be the more effective strategy for improving salt tolerance of conventional crop plants.
Sites of action of sulphite and bisulphite in the photosynthetic apparatus of sugar maple leaves as studied by photo‐acoustic and modulated fluorescence methods
Authors: N'SOUKPOÉ‐KOSSI C. N. , VEERANJANEYULU K. , LEBLANC R. M. 
Published: April 2006

ABSTRACTThe photosynthetic activity of intact sugar maple leaves has been assessed in the presence of exogenous sulphite, bisulphite and sulphate under varying light conditions using photo‐acoustic and modulated fluorescence methods. In the light, bisulphite was found to be more toxic than the other two, sulphate being the least toxic of all. Interestingly, the vitality index, Rrd, measured as the ratio of the modulated fluorescence decrease (Fd) to the steady‐state fluorescence (Fs), which indicates the efficiency of the whole photosynthetic activity, was more affected than the total photosynthetic energy storage (PES) of PSII and PSI during linear and cyclic electron transport, and Fv/Fm(PSII activity). The severity of the damage appeared to be a function of light intensity. Bisulphite treatment in darkness resulted in a dramatic decrease in Rrd, a moderate decrease in PES and a marginal decrease in Fv/Fm. As for sulphite, the effect was negligible with a tendency for enhanced activity. It is inferred that the Calvin cycle is a good candidate for the primary site of bisulphite and sulphite action. Recovery of activity, especially at the Rrdlevel, obtained in the presence of ascorbate, glutathione and L‐cysteine, indicated a contribution of O2free radicals to the observed inhibition of the photosynthetic activity in the light.