Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
 4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Legumes obtain a substantial portion of their nitrogen (N) from symbiotic N2 fixation in root nodules. The glutamine synthetase (GS, EC 6.3.1.2)/glutamate synthase (GOGAT) cycle is responsible for the initial N assimilation. This report describes the analysis of a transgenic alfalfa (Medicago sativa L.) line containing an antisense NADH-GOGAT (EC 1.4.1.14) under the control of the nodule-enhanced aspartate amino-transferase (AAT-2) promoter. In one transgenic line, NADH-GOGAT enzyme activity was reduced to approximately 50%, with a corresponding reduction in protein and mRNA. The transcript abundance for cytosolic GS, ferredoxin-dependent GOGAT (EC 1.4.7.1), AAT-2 (EC 2.6.1.1), asparagine synthase (EC 6.3.5.4), and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) were unaffected, as were enzyme activities for AAT, PEPC and GS. Antisense NADH-GOGAT plants grown under symbiotic conditions were moderately chlorotic and reduced in growth and N content, even though symbiotic N2 fixation was not significantly reduced. The addition of nitrate relieved the chlorosis and restored growth and N content. Surprisingly, the antisense NADH-GOGAT plants were male sterile resulting from inviable pollen. A reduction in NADH-GOGAT enzyme activity and transcript abundance in the antisense plants was measured during the early stages of flower development. Inheritance of the transgene was stable and resulted in progeny with a range of NADH-GOGAT activity. These data indicate that NADH-GOGAT plays a critical role in the assimilation of symbiotically fixed N and during pollen development.
J Exp Bot 2000 Jan
PMID:Decreased NADH glutamate synthase activity in nodules and flowers of alfalfa (Medicago sativa L.) transformed with an antisense glutamate synthase transgene. 1093 93

In maize leaves growth at low temperatures causes decreases in maximum catalytic activities of photosynthetic enzymes and reduced amounts of proteins, rather than effects on regulation or co-ordination of the photosynthetic processes. To test the hypothesis that differential localization of antioxidants between the different types of photosynthetic cell in maize leaves is a major determinant of the extreme sensitivity of maize leaves to chilling damage, oxidative damage to proteins, induced by incubation of maize leaves with paraquat, has been measured and compared with the effects incurred by growth at low temperatures. While the increase in protein carbonyl groups caused by paraquat treatment was much greater than that caused by low temperature growth conditions, most carbonyl groups were detected on bundle sheath proteins in both stress conditions. With one or two exceptions proteins located in the mesophyll tissues were free of protein carbonyl groups in both situations. Paraquat treatment caused a complete loss of the psaA gene products, modified the photosystem II reaction centre polypeptide, D1, and increased the number of peptides arising from breakdown of ribulose 1,5-bisphosphate carboxylase oxygenase (Rubisco). In contrast, growth at 15 degrees C increased the abundance (but not number) of Rubisco breakdown products and decreased that of the psaB gene product while the psaA gene product and PEP carboxylase were largely unaffected. Since bundle sheath proteins are more susceptible to oxidative damage than those located in the mesophyll cells, strategies for achieving a more balanced system of antioxidant defence may be effective in improving chilling tolerance in maize.
J Exp Bot 2000 Jan
PMID:Bundle sheath proteins are more sensitive to oxidative damage than those of the mesophyll in maize leaves exposed to paraquat or low temperatures. 1093 3

Heterozygous mutants of Amaranthus edulis deficient in PEP carboxylase (PEPC) have been used to study the control of photosynthetic carbon assimilation. A reduction in PEPC activity led to a decrease in the initial slope of the relationship between the CO2 assimilation rate and the intercellular CO2 concentration and to a decrease in photosynthesis at high light intensities, consistent with a decrease in the capacity of the C4 cycle in high light. PEPC exerted appreciable control on photosynthetic flux in the wild-type, with a relatively high flux control coefficient of 0.35 in saturating light and ambient CO2. The flux control coefficient was decreased in low light or increased in low CO2 or in plants containing lower PEPC activity. However, the rate of CO2 assimilation decreased down to about 55% PEPC, followed by an up-turn in the light-saturated photosynthetic rate as PEPC was further reduced, suggesting the existence of a mechanism that compensates for the loss of PEPC activity. The amounts of photosynthetic metabolites, including glycine and serine, also showed a biphasic response to decreasing PEPC. There was a linear relationship between the activity of PEPC and the activation state of the enzyme. A possible mechanism of compensation involving photorespiratory intermediates is discussed.
J Exp Bot 2000 Feb
PMID:Control of C4 photosynthesis: effects of reduced activities of phosphoenolpyruvate carboxylase on CO2 assimilation in Amaranthus edulis L. 1093 41

The compartmentation of key processes in sugar, organic acid and amino acid metabolism was studied during the development of the flesh and seeds of grape (Vitis vinifera L.) berries. Antibodies specific for enzymes involved in sugar (cell wall and vacuolar invertases, pyrophosphate: fructose 6-phosphate phosphotransferase, aldolase, NADP-glyceraldehyde-P dehydrogenase, cytosolic fructose 1,6-bisphosphatase), photosynthesis (Rubisco, fructose 1,6-bisphosphatase, sedoheptulose 1,7-bisphosphatase), amino acid metabolism (cytosolic and mitochondrial aspartate aminotransferases, alanine aminotransferase, glutamate dehydrogenase, glutamine synthetase), organic acid metabolism (phosphoenolpyruvate carboxylase, NAD- and NADP-dependent malic enzyme, ascorbate peroxidase), and lipid metabolism (acetyl CoA carboxylase, isocitrate lyase) were used to determine how their abundance changed during development. There were marked changes in the abundance of many of these enzymes in both the flesh and seeds. The intercellular location of some enzymes was investigated using immunohistochemistry. Several enzymes (e.g. phosphoenolpyruvate carboxylase and those involved in amino acid metabolism) were associated with tissues likely to function in the transport of imported assimilates, such as the vasculature. Although other enzymes (e.g. NADP-malic enzyme and soluble acid invertase, involved in the metabolism of sugars and organic acids) were largely present in the parenchyma cells of the flesh, their distribution was extremely heterogeneous. This study shows that when considering the metabolism of complex structures such as fruit, it is essential to consider how metabolism is compartmentalized between and within different tissues, even when they are apparently structurally homogeneous.
J Exp Bot 2000 Apr
PMID:An immunohistochemical study of the compartmentation of metabolism during the development of grape (Vitis vinifera L.) berries. 1093 59

I compared the C(4) grass flora and climatic records for 32 sites in the United States. Consistent with previous studies, I found that the proportion of the grass flora that uses the NADP malic enzyme (NADP-ME) variant of C(4) photosynthesis greatly increases with increasing annual precipitation, while the proportion using the NAD malic enzyme (NAD-ME) variant (and also the less common phosphoenolpyruvate carboxykinase [PCK] variant) decreases. However the association of grass subfamilies with annual precipitation was even stronger than for the C(4) decarboxylation variants. Analysis of the patterns of distribution by partial correlation analysis showed that the correlations between the frequency of various C(4) types and rainfall were solely due to the association of the C(4) types with particular grass subfamilies. In contrast, there was a strong correlation of the frequency of the different subfamilies with annual precipitation that was independent of the influence of the different C(4) variants. It therefore appears that other, as yet unidentified, characteristics that differ among grass subfamilies may be responsible for their differences in distribution across natural precipitation gradients.
Am J Bot 2000 Aug
PMID:Climate and the U.S. distribution of C4 grass subfamilies and decarboxylation variants of C4 photosynthesis. 1094 7

The unique roles of individual cells may be critical to the physiology of an organism. In such cases, micromethods are essential to elucidating the molecular biology, biochemistry and biophysics of the specialized cells or even subcellular compartments of the important cells. The great proliferation of micromethods testifies to their value and no single review can be comprehensive. This review therefore provides only a generalized overview of one approach, namely dissection that provides a pure sample for subsequent extraction and analysis by microdroplet chemistry. As a means of illustrating the utility of this approach, an application-study of the interaction of cytosolic malate concentration and guard-cell phosphoenolpyruvate carboxylase-is provided.
J Exp Bot 2001 Apr
PMID:Single-cell dissection and microdroplet chemistry. 1137 8

The acclimation of C(4) photosynthesis to low temperature was studied in the montane grass Muhlenbergia montana in order to evaluate inherent limitations in the C(4) photosynthetic pathway following chilling. Plants were grown in growth cabinets at 26 degrees C days, but at night temperatures of either 16 degrees C (the control treatment), 4 degrees C for at least 28 nights (the cold-acclimated treatment), or 1 night (the cold-stress treatment). Below a measurement temperature of 25 degrees C, little difference in the thermal response of the net CO(2) assimilation rate (A) was observed between the control and cold-acclimated treatment. By contrast, above 30 degrees C, A in the cold-acclimated treatment was 10% greater than in the control treatment. The temperature responses of Rubisco activity and net CO(2) assimilation rate were similar below 22 degrees C, indicating high metabolic control of Rubisco over the rate of photosynthesis at cool temperatures. Analysis of the response of A to intercellular CO(2) level further supported a major limiting role for Rubisco below 20 degrees C. As temperature declined, the CO(2) saturated plateau of A exhibited large reductions, while the initial slope of the CO(2) response was little affected. This type of response is consistent with a Rubisco limitation, rather than limitations in PEP carboxylase capacity. Stomatal limitations at low temperature were not apparent because photosynthesis was CO(2) saturated below 23 degrees C at air levels of CO(2). In contrast to the response of photosynthesis to temperature and CO(2) in plants acclimated for 4 weeks to low night temperature, plants exposed to 4 degrees C for one night showed substantial reduction in photosynthetic capacity at temperatures above 20 degrees C. Because these reductions were at both high and low CO(2), enzymes associated with the C(4) carbon cycle were implicated as the major mechanisms for the chilling inhibition. These results demonstrate that C(4) plants from climates with low temperature during the growing season can fully acclimate to cold stress given sufficient time. This acclimation appears to involve reversal of injury to the C(4) cycle following initial exposure to low temperature. By contrast, carbon gain at low temperatures generally appears to be constrained by the carboxylation capacity of Rubisco, regardless of acclimation time. The inability to overcome the Rubisco limitation at low temperature may be an inherent limitation restricting C(4) photosynthetic performance in cooler climates.
J Exp Bot 2001 Apr
PMID:The response of the high altitude C(4) grass Muhlenbergia montana (Nutt.) A.S. Hitchc. to long- and short-term chilling. 1141 19

In the leaves of the NAD-malic enzyme (NAD-ME)-type C4 dicot Amaranthus viridis L., there are chloroplasts in the vascular parenchyma cells (VPC), companion cells (CC), ordinary epidermal cells (EC), and guard cells (GC), as well as in the mesophyll cells (MC) and the bundle sheath cells (BSC). However, the chloroplasts of the VPC, CC, EC, and GC are smaller than those of the MC and BSC. In this study, the accumulation of photosynthetic and photorespiratory enzymes in these leaf cell types was investigated by immunogold labelling and electron microscopy. Strong labelling for phosphoenolpyruvate carboxylase was found in the MC cytosol. Weak labelling was observed in the CC and GC cytosol. Labelling for pyruvate, Pi dikinase occurred to varying degrees in the chloroplasts of all cell types except CC. Labelling for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase was detected in the chloroplasts of all cell types except MC. For both NAD-ME and the P-protein of glycine decarboxylase, intense labelling was found in the BSC mitochondria; weaker labelling was recognized in the VPC mitochondria. These data indicate that when not only the MC and BSC but also the other leaf cell types are included, the cell-specific expression of the enzymes in C4 leaves becomes more complex than has been known previously. These findings are discussed in relation to the metabolic function of epidermal and vascular bundle cells.
J Exp Bot 2001 May
PMID:Ultrastructural localization of photosynthetic and photorespiratory enzymes in epidermal, mesophyll, bundle sheath, and vascular bundle cells of the C4 dicot Amaranthus viridis. 1143 17

To improve the efficiency of CO(2) fixation in C(3) photosynthesis, C(4)-cycle genes were overexpressed in potato and tobacco plants either individually or in combination. Overexpression of the phosphoenolpyruvate carboxylase (PEPC) gene (ppc) from Corynebacterium glutamicum (cppc) or from potato (stppc, deprived of the phosphorylation site) in potato resulted in a 3-6-fold induction of endogenous cytosolic NADP malic enzyme (ME) and an increase in the activities of NAD-ME (3-fold), NADP isocitrate dehydrogenase (ICDH), pyruvate kinase (PK), NADP glycerate-3-P dehydrogenase (NADP-GAPDH), and PEP phosphatase (PEPP). In double transformants overexpressing cppc and chloroplastic NADP-ME from Flaveria pringlei (fpMe1), cytosolic NADP-ME was less induced and pleiotropic effects were diminished. There were no changes in enzyme pattern in single fpMe1 overexpressors. In cppc overexpressors of tobacco, the increase in endogenous cytosolic NADP-ME activity was small and changes in other enzymes were less pronounced. Determinations of the CO(2) compensation point (Gamma*) as well as temperature and oxygen effects on photosynthesis produced variational data suggesting that the desired decline in photorespiration occurred only under certain experimental conditions. Double transformants of potato (cppc/fpMe1) exhibited the most consistent attenuating effect on photorespiration. In contrast, photorespiration in tobacco plants appeared to be diminished most in single cppc overexpressors rather than in double transformants (cppc/fpMe1). In tobacco, introduction of the PEP carboxykinase (PEPCK) gene from the bacterium Sinorhizobium meliloti (pck) had little effect on photosynthetic parameters in single (pck) and double transformants (cppc/pck). In transgenic potato plants, increased PEPC activities resulted in a decline in UV protectants (flavonoids) in single cppc or stppc transformants, but not in double transformants (cppc/fpMe1). PEP provision to the shikimate pathway inside the plastids, from which flavonoids derive, might be restricted only in single PEPC overexpressors.
J Exp Bot 2001 Sep
PMID:Single and double overexpression of C(4)-cycle genes had differential effects on the pattern of endogenous enzymes, attenuation of photorespiration and on contents of UV protectants in transgenic potato and tobacco plants. 1152 Aug 67

The process of photorespiration diminishes the efficiency of CO(2) assimilation and yield of C(3)-crops such as wheat, rice, soybean or potato, which are important for feeding the growing world population. Photorespiration starts with the competitive inhibition of CO(2) fixation by O(2) at the active site of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and can result in a loss of up to 50% of the CO(2) fixed in ambient air. By contrast, C(4) plants, such as maize, sugar cane and Sorghum, possess a CO(2) concentrating mechanism, by which atmospheric CO(2) is bound to C(4)-carbon compounds and shuttled from the mesophyll cells where the prefixation of bicarbonate occurs via phosphoenolpyruvate carboxylase (PEPC) into the gas-tight bundle-sheath cells, where the bound carbon is released again as CO(2) and enters the Calvin cycle. However, the anatomical division into mesophyll and bundle-sheaths cells ("Kranz"-anatomy) appears not to be a prerequisite for the operation of a CO(2) concentrating mechanism. Submerged aquatic macrophytes, for instance, can induce a C(4)-like CO(2) concentrating mechanism in only one cell type when CO(2) becomes limiting. A single cell C(4)-mechanism has also been reported recently for a terrestrial chenopod. For over 10 years researchers in laboratories around the world have attempted to improve photosynthesis and crop yield by introducing a single cell C(4)-cycle in C(3) plants by a transgenic approach. In the meantime, there has been substantial progress in overexpressing the key enzymes of the C(4) cycle in rice, potato, and tobacco. In this review there will be a focus on biochemical and physiological consequences of the overexpression of C(4)-cycle genes in C(3) plants. Bearing in mind that C(4)-cycle enzymes are also present in C(3) plants, the pitfalls encountered when C(3) metabolism is perturbed by the overexpression of individual C(4) genes will also be discussed.
J Exp Bot 2002 Apr
PMID:Overexpression of C(4)-cycle enzymes in transgenic C(3) plants: a biotechnological approach to improve C(3)-photosynthesis. 1188 79


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