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Steven J Craftsbrandner - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of photosynthesis in a c4 plant maize to heat stress
Plant Physiology, 2002Co-Authors: Steven J Craftsbrandner, Michael E SalvucciAbstract:Our objective was to determine the sensitivity of components of the photosynthetic apparatus of maize (Zea mays), a C4 plant, to high temperature stress. Net photosynthesis (Pn) was inhibited at leaf temperatures above 38°C, and the inhibition was much more severe when the temperature was increased rapidly rather than gradually. Transpiration rate increased progressively with leaf temperature, indicating that inhibition was not associated with stomatal closure. Nonphotochemical fluorescence quenching (qN) increased at leaf temperatures above 30°C, indicating increased thylakoid energization even at temperatures that did not inhibit Pn. Compared with CO2 assimilation, the maximum quantum yield of photosystem II (Fv/Fm) was relatively insensitive to leaf temperatures up to 45°C. The activation state of phosphoenolpyruvate carboxylase decreased marginally at leaf temperatures above 40°C, and the activity of pyruvate phosphate dikinase was insensitive to temperature up to 45°C. The activation state of Rubisco decreased at temperatures exceeding 32.5°C, with nearly complete inactivation at 45°C. Levels of 3-Phosphoglyceric Acid and ribulose-1,5-bisphosphate decreased and increased, respectively, as leaf temperature increased, consistent with the decrease in Rubisco activation. When leaf temperature was increased gradually, Rubisco activation acclimated in a similar manner as Pn, and acclimation was associated with the expression of a new activase polypeptide. Rates of Pn calculated solely from the kinetics of Rubisco were remarkably similar to measured rates if the calculation included adjustment for temperature effects on Rubisco activation. We conclude that inactivation of Rubisco was the primary constraint on the rate of Pn of maize leaves as leaf temperature increased above 30°C.
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inhibition and acclimation of photosynthesis to heat stress is closely correlated with activation of ribulose 1 5 bisphosphate carboxylase oxygenase
Plant Physiology, 1999Co-Authors: David R Law, Steven J CraftsbrandnerAbstract:Increasing the leaf temperature of intact cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.) plants caused a progressive decline in the light-saturated CO2-exchange rate (CER). CER was more sensitive to increased leaf temperature in wheat than in cotton, and both species demonstrated photosynthetic acclimation when leaf temperature was increased gradually. Inhibition of CER was not a consequence of stomatal closure, as indicated by a positive relationship between leaf temperature and transpiration. The activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), which is regulated by Rubisco activase, was closely correlated with temperature-induced changes in CER. Nonphotochemical chlorophyll fluorescence quenching increased with leaf temperature in a manner consistent with inhibited CER and Rubisco activation. Both nonphotochemical fluorescence quenching and Rubisco activation were more sensitive to heat stress than the maximum quantum yield of photochemistry of photosystem II. Heat stress led to decreased 3-Phosphoglyceric Acid content and increased ribulose-1,5-bisphosphate content, which is indicative of inhibited metabolite flow through Rubisco. We conclude that heat stress inhibited CER primarily by decreasing the activation state of Rubisco via inhibition of Rubisco activase. Although Rubisco activation was more closely correlated with CER than the maximum quantum yield of photochemistry of photosystem II, both processes could be acclimated to heat stress by gradually increasing the leaf temperature.
H. E. Neuhaus - One of the best experts on this subject based on the ideXlab platform.
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starch degradation in chloroplasts isolated from c3 or cam crassulacean Acid metabolism induced mesembryanthemum crystallinum l
Biochemical Journal, 1996Co-Authors: H. E. Neuhaus, N SchulteAbstract:C3 or crassulacean Acid metabolism (CAM)-induced Mesembryanthemum crystallinum plants perform nocturnal starch degradation which is linear with time. To analyse the composition of metabolites released by isolated leaf chloroplasts during starch degradation we developed a protocol for the purification of starch-containing plastids. Isolated chloroplasts from C3 or CAM-induced M. crystallinum plants are also able to degrade starch. With respect to the endogenous starch content of isolated plastids the rate of starch degradation in intact leaves. The combined presence of Pi, ATP, and oxaloacetate is identified to be the most positive effector combination to induce starch mobilization. The metabolic flux through the oxidative pentose-phosphate pathway in chloroplasts isolated from CAM-induced M. crystallinum is less than 3.5% compared with other metabolic routes of starch degradation. Here we report that starch-degrading chloroplasts isolated from CAM-induced M. crystallinum plants use exogenously supplied oxaloacetate for the synthesis of malate. The main products of starch degradation exported into the incubation medium by these chloroplasts are glucose 6-phosphate, 3-Phosphoglyceric Acid, dihydroxyacetone phosphate and glucose. The identification of glucose 6-phosphate as an important metabolite released during starch degradation is in contrast to the observations made on all other types of plastids analysed so far, including chloroplasts isolated from M. crystallinum in the C3 state. Therefore, we analysed the transport properties of isolated chloroplasts from M. crystallinum. Surprisingly, both types of chloroplasts, isolated from either C3 or CAM-induced plants, are able to transport glucose 6-phosphate in counter exchange with endogenous Pi, indicating the presence of a glucose 6-phosphate translocator as recently demonstrated to occur in other types of plastids. The composition of metabolites released and the stimulatory effect of oxaloacetate on the rate of starch degradation are discussed with respect to the Acidification observed for CAM leaves during the night.
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Induction of Hexose-Phosphate Translocator Activity in Spinach Chloroplasts.
Plant physiology, 1995Co-Authors: William Paul Quick, R. Scheibe, H. E. NeuhausAbstract:Many environmental and experimental conditions lead to accumulation of carbohydrates in photosynthetic tissues. This situation is typically associated with major changes in the mRNA and protein complement of the cell, including metabolic repression of photosynthetic gene expression, which can be induced by feeding carbohydrates directly to leaves. In this study we examined the carbohydrate transport properties of chloroplasts isolated from spinach (Spinacia oleracea L.) leaves fed with glucose for several days. These chloroplasts contain large quantities of starch, can perform photosynthetic 3-phosphoglycerate reduction, and surprisingly also have the ability to perform starch synthesis from exogenous glucose-6-phosphate (Glc-6-P) both in the light and in darkness, similarly to heterotrophic plastids. Glucose-1-phosphate does not act as an exogenous precursor for starch synthesis. Light, ATP, and 3-Phosphoglyceric Acid stimulate Glc-6-P-dependent starch synthesis. Short-term uptake experiments indicate that a novel Glc-6-P-translocator capacity is present in the envelope membrane, exhibiting an apparent Km of 0.54 mM and a Vmax of 2.9 [mu]mol Glc-6-P mg-1 chlorophyll h-1. Similar results were obtained with chloroplasts isolated from glucose-fed potato leaves and from water-stressed spinach leaves. The generally held view that sugar phosphates transported by chloroplasts are confined to triose phosphates is not supported by these results. A physiological role for a Glc-6-P translocator in green plastids is presented with reference to the source/sink function of the leaf.
Yinhui Yua - One of the best experts on this subject based on the ideXlab platform.
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effects of exogenous spermidine on photosynthetic capacity and expression of calvin cycle genes in salt stressed cucumber seedlings
Journal of Plant Research, 2014Co-Authors: Sheng Shu, Lifang Che, Shirong Guo, Yinhui YuaAbstract:We investigated the effects of exogenous spermidine (Spd) on growth, photosynthesis and expression of the Calvin cycle-related genes in cucumber seedlings (Cucumis sativus L.) exposed to NaCl stress. Salt stress reduced net photosynthetic rates (PN), actual photochemical efficiency of PSII (ΦPSII) and inhibited plant growth. Application of exogenous Spd to salinized nutrient solution alleviated salinity-induced the inhibition of plant growth, together with an increase in PN and ΦPSII. Salinity markedly reduced the maximum carboxylase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Vcmax), the maximal velocity of RuBP regeneration (Jmax), triose-phosphate utilization capacity (TPU) and carboxylation efficiency (CE). Spd alleviated the negative effects on CO2 assimilation induced by salt stress. Moreover, Spd significantly increased the activities and contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and fructose-1,6-biphosphate aldolase (ALD; aldolase) in the salt-stressed cucumber leaves. On the other hand, salinity up-regulated the transcriptional levels of ribulose-1,5-bisphosphate (RCA), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoribrokinase (PRK) and down-regulated the transcriptional levels of ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (RbcL), ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit (RbcS), ALD, triose-3-phosphate isomerase (TPI), fructose-1,6-bisphosphate phosphatase (FBPase) and 3-Phosphoglyceric Acid kinase (PGK). However, Spd application to salt-stressed plant roots counteracted salinity-induced mRNA expression changes in most of the above-mentioned genes. These results suggest that Spd could improve photosynthetic capacity through regulating gene expression and activity of key enzymes for CO2 fixation, thus confers tolerance to salinity on cucumber plants.
David R Law - One of the best experts on this subject based on the ideXlab platform.
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inhibition and acclimation of photosynthesis to heat stress is closely correlated with activation of ribulose 1 5 bisphosphate carboxylase oxygenase
Plant Physiology, 1999Co-Authors: David R Law, Steven J CraftsbrandnerAbstract:Increasing the leaf temperature of intact cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.) plants caused a progressive decline in the light-saturated CO2-exchange rate (CER). CER was more sensitive to increased leaf temperature in wheat than in cotton, and both species demonstrated photosynthetic acclimation when leaf temperature was increased gradually. Inhibition of CER was not a consequence of stomatal closure, as indicated by a positive relationship between leaf temperature and transpiration. The activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), which is regulated by Rubisco activase, was closely correlated with temperature-induced changes in CER. Nonphotochemical chlorophyll fluorescence quenching increased with leaf temperature in a manner consistent with inhibited CER and Rubisco activation. Both nonphotochemical fluorescence quenching and Rubisco activation were more sensitive to heat stress than the maximum quantum yield of photochemistry of photosystem II. Heat stress led to decreased 3-Phosphoglyceric Acid content and increased ribulose-1,5-bisphosphate content, which is indicative of inhibited metabolite flow through Rubisco. We conclude that heat stress inhibited CER primarily by decreasing the activation state of Rubisco via inhibition of Rubisco activase. Although Rubisco activation was more closely correlated with CER than the maximum quantum yield of photochemistry of photosystem II, both processes could be acclimated to heat stress by gradually increasing the leaf temperature.
Peter Setlow - One of the best experts on this subject based on the ideXlab platform.
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Release of small molecules during germination of spores of Bacillus species
2008Co-Authors: Barbara Setlow, Paul G. Wahome, Peter SetlowAbstract:Free amino Acids, dipicolinic Acid, and unidentified small molecules were released early in Bacillus spore germination before hydrolysis of the peptidoglycan cortex, but adenine nucleotides and 3-phosphoglycerate were not. These results indicate that early in germination there is a major selective change in the permeability of the spore’s inner membrane. Dormant spores of Bacillus species contain a number of small molecules in their central region or core that become the protoplast of the growing cell. The small molecule present in spores at the highest level (600 mol/g [dry weight]) is pyr-idine-2,6-dicarboxylic Acid (dipicolinic Acid [DPA]), which is largely present as a 1:1 chelate with divalent cations, predom-inantly Ca2 (Ca-DPA) (17). However, levels of glutamic Acid (20 to 25 mol/g [dry weight]), arginine (10 mol/g [dry weight]), 3-Phosphoglyceric Acid (3PGA) (5 to 20 mol/g [dr
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structure and mechanism of action of a novel phosphoglycerate mutase from bacillus stearothermophilus
The EMBO Journal, 2000Co-Authors: Mark J Jedrzejas, Peter Setlow, Monica Chander, Gunasekaran KrishnasamyAbstract:Bacillus stearothermophilus phosphoglycerate mutase (PGM), which interconverts 2- and 3-Phosphoglyceric Acid (PGA), does not require 2,3-diphosphoglyceric Acid for activity. However, this enzyme does have an absolute and specific requirement for Mn(2+) ions for catalysis. Here we report the crystal structure of this enzyme complexed with 3PGA and manganese ions to 1.9 A resolution; this is the first crystal structure of a diphosphoglycerate-independent PGM to be determined. This information, plus the location of the two bound Mn(2+) ions and the 3PGA have allowed formulation of a possible catalytic mechanism for this PGM. In this mechanism Mn(2+) ions facilitate the transfer of the substrate's phosphate group to Ser62 to form a phosphoserine intermediate. In the subsequent phosphotransferase part of the reaction, the phosphate group is transferred from Ser62 to the O2 or O3 positions of the reoriented glycerate to yield the PGA product. Site-directed mutagenesis studies were used to confirm our mechanism and the involvement of specific enzyme residues in Mn(2+) binding and catalysis.
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The internal pH of the forespore compartment of Bacillus megaterium decreases by about 1 pH unit during sporulation
1994Co-Authors: Nancy G. Magill, Ann E. Cowan, Dennis E. Koppel, Peter SetlowAbstract:Previous work has shown that the internal pH of dormant spores of Bacillus species is more than 1 pH Ubelow that of growing cells but rises to that of growing cells in the first minutes of spore germination. In thepresent work the internal pH of the whole Bacillus megaterium sporangium was measured by the distribution of the weak base methylamine and was found to decrease by-0.4 during sporulation. By using fluorescence ratio image analysis with a fluorescein derivative, 2',7'-bis(2-carboxyethyl)-5 (and-6)-carboxyfluorescein(BCECF), whose fluorescence is pH sensitive, the internal pH of the mother cell was found to remain constantduring sporulation at a value of 8.1, similar to that in the vegetative cell. Whereas the internal pH of theforespore was initially-8.1, this value fell to-7.0 approximately 90 min before synthesis of dipicolinic Acid and well before accumulation of the depot of 3-Phosphoglyceric Acid. The pH in the forespore compartment wasbrought to that of the mother cell by suspending sporulating cells in a pH 8 potassium phosphate buffer plusthe ionophore nigericin to clamp the internal pH of the cells to that of the external medium. We suggest that at a minimum, Acidification of the forespore may regulate the activity of phosphoglycerate mutase, which is the enzyme known to be regulated to allow 3-Phosphoglyceric Acid accumulation during sporulation. Bacteria of the gram-positive Bacillus and Clostridium spe-cies undergo a developmental process called sporulation in response to starvation for a variety of nutrients (4). An early morphological event in sporulation is the synthesis of an asymmetric septum which divides the sporangium into the larger mother cell and smaller forespore compartments. The forespore compartment is then engulfed by the mother cell and eventually develops into the mature spore, which is released into the medium upon lysis of the mother cell. The matur
