Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.7.1.2 (nitrate reductase)
3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interactions between sulphur nutrition and Cd exposure were investigated in maize (Zea mays L.) plants. Plants were grown for 12 days in nutrient solution with or without sulphate. Half of the plants of each treatment were then supplied with 100 microM Cd. Leaves were collected 0, 1, 2, 3, 4 and 5 days from the beginning of Cd application and used for chemical analysis and enzyme assays. Cd exposure produced symptoms of toxicity (leaf chlorosis, growth reduction) and induced a noticeable accumulation of non-protein SH compounds. As phytochelatins are glutamate- and cysteine-rich peptides, the effect of cadmium on some enzyme activities involved in N and S metabolism of maize leaves was studied in relation to the plant sulphur supply. In vivo Cd application to S-sufficient plants resulted in a drop of all measured enzyme activities. On the other hand, S-deficient plants showed a decrease in nitrate reductase (NR; EC 1.6.6.1) and glutamine synthetase (GS; EC 6.3.1.2) activity, and an increase in NAD-dependent glutamate dehydrogenase (GDH; EC 1.4.1.2) and phosphoenolpyruvate carboxylase (PEPc; EC 4.1.1.31) activity as a result of the Cd treatment. Furthermore, in the same plants ATP sulphurylase (ATPs; EC 2.7.7.4) and O-acetylserine sulphydrylase (OASs; EC 4.2.99.8) showed a particular pattern as both enzymes exhibited a transient maximum value of activity after 4 days from the beginning of Cd exposure. Results provide evidence that the increase of ATPs, OASs, GDH and PEPc activities, observed exclusively in S-deficient Cd-treated plants, may be part of the defence mechanism based on the production of phytochelatins.
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PMID:Role of sulphur availability on cadmium-induced changes of nitrogen and sulphur metabolism in maize (Zea mays L.) leaves. 1531 68

Prochlorococcus is one of the dominant cyanobacteria and a key primary producer in oligotrophic intertropical oceans. Here we present an overview of the pathways of nitrogen assimilation in Prochlorococcus, which have been significantly modified in these microorganisms for adaptation to the natural limitations of their habitats, leading to the appearance of different ecotypes lacking key enzymes, such as nitrate reductase, nitrite reductase, or urease, and to the simplification of the metabolic regulation systems. The only nitrogen source utilizable by all studied isolates is ammonia, which is incorporated into glutamate by glutamine synthetase. However, this enzyme shows unusual regulatory features, although its structural and kinetic features are unchanged. Similarly, urease activities remain fairly constant under different conditions. The signal transduction protein P(II) is apparently not phosphorylated in Prochlorococcus, despite its conserved amino acid sequence. The genes amt1 and ntcA (coding for an ammonium transporter and a global nitrogen regulator, respectively) show noncorrelated expression in Prochlorococcus under nitrogen stress; furthermore, high rates of organic nitrogen uptake have been observed. All of these unusual features could provide a physiological basis for the predominance of Prochlorococcus over Synechococcus in oligotrophic oceans.
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PMID:Streamlined regulation and gene loss as adaptive mechanisms in Prochlorococcus for optimized nitrogen utilization in oligotrophic environments. 1559 Jul 77

In tobacco, the two enzymes of nitrogen metabolism, cytosolic glutamine synthetase (GS1; E.C.6.3.1.2) and glutamate dehydrogenase (GDH; E.C.1.4.1.2), are induced during leaf senescence, whereas the chloroplastic glutamine synthetase (GS2; E.C.6.3.1.2) and nitrate reductase (NR; E.C.1.6.1.1) are repressed in the course of ageing. In this report, we showed in discs of fully expanded Nicotiana tabacum L. cv. Xanthi leaves that sucrose (Suc) and amino acids were involved in the regulation of the expression of GS1 and GDH genes. Suc induced the expression of GS1 and repressed that of GDH. Therefore, we concluded that in response to Suc, GS1 behaved as an "early" Senescence Associated Gene (SAG), whereas GDH behaved as a "late" SAG. Moreover, amino acids induced the expression of both genes. Among the amino acids tested as signal molecules, proline (Pro) and glutamate (Glu) were major inducers of GDH and GS1 expression, respectively. Interestingly, an opposite regulation of GS1 and GS2 by Pro and Glu was shown. The contrary effect of Suc on NIA (NR encoding gene) and GDH mRNA accumulation was also emphasized.
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PMID:The two nitrogen mobilisation- and senescence-associated GS1 and GDH genes are controlled by C and N metabolites. 1565 37

Effects of atmospheric carbon dioxide enrichment on nitrogen metabolism were studied in barley primary leaves (Hordeum vulgare L. cv. Brant). Seedlings were grown in chambers under ambient (36 Pa) and elevated (100 Pa) carbon dioxide and were fertilized daily with complete nutrient solution providing 12 millimolar nitrate and 2.5 millimolar ammonium. Foliar nitrate and ammonium were 27% and 42% lower (P </= 0.01) in the elevated compared to ambient carbon dioxide treatments, respectively. Enhanced carbon dioxide affected leaf ammonium levels by inhibiting photorespiration. Diurnal variations of total nitrate were not observed in either treatment. Total and Mg(2+)inhibited nitrate reductase activities per gram fresh weight were slightly lower (P </= 0.01) in enhanced compared to ambient carbon dioxide between 8 and 15 DAS. Diurnal variations of total nitrate reductase activity in barley primary leaves were similar in either treatment except between 7 and 10 h of the photoperiod when enzyme activities were decreased (P </= 0.05) by carbon dioxide enrichment. Glutamate was similar and glutamine levels were increased by carbon dioxide enrichment between 8 and 13 DAS. However, both glutamate and glutamine were negatively impacted by elevated carbon dioxide when leaf yellowing was observed 15 and 17 DAS. The above findings showed that carbon dioxide enrichment produced only slight modifications in leaf nitrogen metabolism and that the chlorosis of barley primary leaves observed under enhanced carbon dioxide was probably not attributable to a nutritionally induced nitrogen limitation.
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PMID:Responses of nitrogen metabolism in N-sufficient barley primary leaves to plant growth in elevated atmospheric carbon dioxide. 1622 42

Anabaena cylindrica grown with nitrate required higher levels of sodium (0.4 meq/l NaCl) to prevent chlorosis than when grown without combined nitrogen (0.004 meq/l NaCl). Nitrite accumulated in sodium-deficient cultures containing nitrate. Amounts of nitrite similar to those found in deficient cultures when added to normal cultures resulted in a chlorosis of the cells. Thus loss of chlorophyll was caused by nitrite toxicity.A deficiency of sodium resulted in an increased incorporation of (15)NO(3), (15)NO(2), (15)NH(3) or (14)C glutamate into protein compared with normal cells. The enzyme nitrate reductase was markedly increased in cells grown without sodium.Evidence from chloramphenicol treatment of the cells suggests that sodium may exert its control of nitrate reductase through a protein factor(s).By contrast, N(2) fixation was reduced in sodium deficient cells. Since the incorporation of ammonia or glutamate into protein was increased under these conditions, it is likely that the element is required for the conversion of N(2) gas into ammonia. Various nitrogenous compounds including ammonium chloride, amides and amino acids at low concentrations (0.1 mm) greatly reduced the nitrite accumulation in sodium-deficient cultures.
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PMID:Some Effects of Sodium on Nitrate Assimilation and N(2) Fixation in Anabaena cylindrica. 1665 97

The induction of nitrate reductase activity in root tips of cotton (Gossypium hirsutum L.) was regulated by several amino acids and by ammonium. Glycine, glutamine, and asparagine strongly inhibited induction of activity by nitrate and also decreased growth of sterile-cultured roots on a nitrate medium. Methionine, serine, and alanine weakly inhibited induction, and 11 other amino acids had little or no effect. Ammonium also decreased induction in root tips, but was most effective only at pH 7 or higher. The optimum conditions for ammonium regulation of induction were identical to those for growth of sterile-cultured roots on ammonium as the sole nitrogen source. Aspartate and glutamate strongly stimulated induction, but several lines of evidence indicated that the mechanism of this response was different from that elicited by the other amino acids. The effects of amino acids on induction appeared to be independent of nitrate uptake.In green shoot tissues, all attempts to demonstrate regulation of induction by amino acids failed. The great difference in observed responses of root and shoot to amino acids suggests that their nitrate reductase activities are regulated differently. Differential regulation of this enzyme is consistent with the responses of root and shoot nitrate reductase activity to nitrate.
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PMID:Differential regulation of nitrate reductase induction in roots and shoots of cotton plants. 1665 46

The effect of various day temperatures on NADH-nitrate reductase, NADH- and NADPH-glutamate dehydrogenases, nitrate, protein and leaf area, measured at intervals during the ontogeny of the first trifoliolate soybean leaf, was determined. At 32.5 C and 25 C, nitrate concentration, nitrate reductase, and NADPH-glutamate dehydrogenase activities increased concurrently with leaf development and then decreased as leaf maturation progressed. At 40 C, these three components showed no initial increase and the concentration or activities decreased throughout the development of the leaf. The effects of temperature on NADH-glutamate dehydrogenase were the reverse. Rates of protein accumulation were higher at 40 C during the first 2 days of leaf development while higher rates were measured the first 5 days of leaf growth at 32.5 C. At 25 C, protein accumulation was low during the first 3 days of leaf growth, increased in the period of 3 to 5 days, and then declined up to 8 days of leaf development. Leaf expansion progressed at faster rates at 32.5 C and 25 C and at a much slower rate at 40 C. Leaf growth was essentially complete after the fifth day regardless of temperature.In crude leaf homogenates, apparent irreversible inactivation temperatures were 36 C for nitrate reductase and 65 C for NADPH-glutamate dehydrogenase. In vivo studies indicated a lower inactivation temperature for NADPH-glutamate dehydrogenase; however, it was still more heat-tolerant than nitrate reductase.We envisaged that reduced nitrogen supplied by NO(3) (-) assimilation is a factor in leaf expansion.
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PMID:Influence of Temperature on Nitrate Metabolism and Leaf Expansion in Soybean (Glycine max L. Merr.) Seedlings. 1665 11

Excised 7-day-old oat (Avena sativa L. cv. Jaycee) leaves were incubated in media containing 7.1 millimolar KNO(3) and 0.15 millimolar tabtoxin or 1 millimolar methionine sulfoximine (MSO) to investigate the sources of the observed ammonium accumulated. Tabtoxin and MSO are known inhibitors of glutamine synthetase, the first enzyme in the primary pathway of ammonium assimilation. During a 4- to 6-hour incubation, there was little net change in protein or total amino acid concentration. Alanine, aspartate/asparagine, and glutamate/glutamine decreased markedly under these treatments, whereas several other amino acids increased. Exogenous (15)N from K(15)NO(3) was taken up and incorporated into the nitrate and ammonium fractions of leaves treated with tabtoxin or MSO. This result and the high in vitro activities of nitrate reductase indicated that reduction of nitrate was one source of the accumulated ammonium. Leaves incubated under 2% O(2) to reduce photorespiration accumulated only about 13% as much ammonium as did those under normal atmospheres. We conclude that most of the tabtoxin- or MSO-induced ammonium came from photo-respiration, and the remainder was from nitrate reduction.
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PMID:Sources of ammonium in oat leaves treated with tabtoxin or methionine sulfoximine. 1666 6

The present study shows for the first time the influence of exogenously applied amino acids and cytokinin on the physiological and molecular aspects of N metabolism in poplar trees. In a short-term feeding experiment, glutamine or trans-zeatin riboside (tZR) was added directly to the nutrient solution. NO3- net uptake declined significantly in response to both treatments. Feeding with glutamine brought about an increase in concentrations of different amino compounds in the roots (glutamine, glutamate, alanine, gamma-amino butyric acid (GABA) and NH4+, which negatively correlated with the net NO3- uptake. The plants showed a reduction of cytosolic glutamine synthetase 1 (GS1) transcript level in the roots. In addition, glutamine feeding changed the root-to-shoot distribution on N assimilation in favour of the leaves and plant internal N cycling. tZR treatment resulted in expansion of zeatin-type (Z-type) cytokinins in the roots and increased nitrate reductase (NR)-mRNA level. The results indicate that both particular amino acids and active cytokinins are involved in the feedback regulation of N uptake and metabolism in poplar. We propose that inhibition of N uptake by cytokinins in poplar is more complex than that mediated by amino compounds, and other effectors are involved in this regulation.
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PMID:Exogenous supply of glutamine and active cytokinin to the roots reduces NO3- uptake rates in poplar. 1708 Sep 50

This paper investigates the influence of the carbon (C) and nitrogen (N) status on the amino acid profile in tobacco source leaves. Treatments used included growing plants at different light intensities, using an antisense RBCS (small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase) construct to inhibit Rubisco activity, growing plants on 12 or 0.5 mM nitrate, comparing wild-types with genotypes that have small and large decreases in nitrate reductase (NIA) activity, and sampling plants at different times during the diurnal cycle. This combination of experiments provides information on how amino acid levels respond to several inputs including the C and N status, nitrate, excess light and light-dark transitions. The data set was analysed using principal component analysis, regression analysis and by normalizing the level of each individual amino acid on the total amino acid pool. Most amino acids show a downward trend when the C or the N status is decreased, and rise during day and fall at night during the diurnal cycle. However, individual amino acids often showed deviating responses. Furthermore, no evidence was found for feedback inhibition of minor amino acid synthesis, either within or between pathways, when 18 individual amino acids were supplied to detached leaves. Results indicate that regulation of amino acid metabolism, for example by the C and N status, leads to qualitatively similar responses of many amino acids, but homeostatic mechanisms involving feedback inhibition within or between individual amino acid biosynthesis pathways are not stringent. All of the above inputs affect the level of phenylalanine, an amino acid that is also the substrate for an important sector of secondary metabolism. The levels of glutamate were remarkably constant, indicating that unknown mechanisms stabilize the concentration of this key central amino acid. Analyses of metabolite levels and feeding experiments indicated that 2-oxoglutarate plays an important role in regulating glutamate levels. Glutamate was the most effective inhibitor of NIA activity when 18 individual amino acids were supplied to detached leaves. Feeding glutamate, and other downstream amino acids, led to an increase of glutamine, indicating glutamate exerts feedback regulation on ammonium metabolism.
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PMID:Impact of the C-N status on the amino acid profile in tobacco source leaves. 1708 Dec 41


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