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 nitrate assimilation pathway represents a useful model system in which to study the contribution of a mycorrhizal fungus to the nitrogen nutrition of its host plant. In the present work we cloned and characterized the nitrate reductase gene (tbnr1) from Tuber borchii. The coding region of tbnr1 is 2,787 nt in length, and it encodes a protein of 929 amino acids. Biochemical and Northern-blot analyses revealed that nitrate assimilation in T. borchii is an inducible system that responds mainly to nitrate. Furthermore, we cloned a nitrate reductase cDNA (tpnr1) from Tilia platyphyllos to set up a quantitative real-time PCR assay that would allow us to determine the fungal contribution to nitrate assimilation in ectomycorrhizal tissue. Using this approach we demonstrated that the level of tbnr1 expression in ectomycorhizae is eight times higher than in free-living mycelia, whereas tpnr1 transcription was found to be down-regulated after the establishment of the symbiosis. Enzymatic assays showed that NADPH-dependent nitrite formation markedly increases in ectomycorrhizae. These findings imply that the fungal partner plays a fundamental role in nitrate assimilation by ectomycorrhizae. Amino acid determination by HPLC revealed higher levels of glutamate, glutamine and asparagine in symbiotic tissues compared with mycelial controls, thus suggesting that these amino acids may represent the compounds that serve to transfer nitrogen to the host plant.
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PMID:Characterization of the Tuber borchii nitrate reductase gene and its role in ectomycorrhizae. 1289 21

Tomato (Lycopersicon esculentum) seedlings were grown in the presence of cadmium. After 1 week of Cd treatment, a sharp decline in biomass accumulation in the leaves and roots was observed, together with a decrease in the rate of photosynthetic activity due to both Rubisco and chlorophyll degradation and stomata closure. Cadmium induced a significant decrease in nitrate content and inhibition of the activities of nitrate reductase, nitrite reductase, glutamine synthetase (GS) and ferredoxin-glutamate synthase. An increase in NADH-glutamate synthase and NADH-glutamate dehydrogenase activity was observed in parallel. The accumulation of ammonium into the tissues of treated plants was accompanied by a loss of total protein and the accumulation of amino acids. Gln represented the major amino acid transported through xylem sap of Cd-treated and control plants. Cadmium treatment increased the total amino acid content in the phloem, maintaining Gln/Glu ratios. Western and Northern blot analysis of Cd-treated plants showed a decrease in chloroplastic GS protein and mRNA and an increase in cytosolic GS and glutamate dehydrogenase transcripts and proteins. An increase in asparagine synthetase mRNA was observed in roots, in parallel with a strong increase in asparagine. Taken together, these results suggest that the plant response to Cd stress involved newly induced enzymes dedicated to coordinated leaf nitrogen remobilization and root nitrogen storage.
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PMID:Cadmium toxicity induced changes in nitrogen management in Lycopersicon esculentum leading to a metabolic safeguard through an amino acid storage strategy. 1557 44

Diurnal variations in nitrate reductase (NR) activity and nitrogen metabolites were examined in wild-type Nicotiana plumbaginifolia and transformants with various degrees of NR deregulation. In the C1 line, NR was only deregulated at the transcriptional level by placing the NR gene under the control of the cauliflower mosaic virus 35S RNA promoter. In the Del8 and S521D lines, NR was additionally deregulated at the posttranslational level either by a deletion mutation in the N-terminal domain or by a mutation of the regulatory phosphorylation site (serine-521). Posttranslational regulation was essential for pronounced diurnal variations in NR activity. Low nitrate content was related to deregulation of NR, whereas the level of total free amino acids was much higher in plants with fully deregulated NR. Abolishing transcriptional and posttranslational regulation (S521D plants) resulted in an increase of glutamine and asparagine by a factor of 9 and 14, respectively, compared with wild type, whereas abolishing transcriptional regulation (C1 plants) only resulted in increases of glutamine and asparagine by factors <2. Among the minor amino acids, isoleucine and threonine, in particular, showed enhanced levels in S521D. Nitrate uptake rates were the same in S521D and wild type as determined with (15)N feeding. Deregulation of NR appears to set the level of certain amino acids, whereas diurnal variations were still determined by light/dark. Generally, deregulation of NR at the transcriptional level did not have much influence on metabolite levels, but additional deregulation at the posttranslational level resulted in profound changes of nitrogen metabolite levels.
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PMID:Posttranslational regulation of nitrate reductase strongly affects the levels of free amino acids and nitrate, whereas transcriptional regulation has only minor influence. 1646 78

A nitrate uptake system is induced (along with nitrate reductase) when NH(4) (+)-grown Penicillium chrysogenum is incubated with inorganic nitrate in synthetic medium in the absence of NH(4) (+). Nitrate uptake and nitrate reduction are probably in steady state in fully induced mycelium, but the ratios of the two activities are not constant during the induction period. Substrate concentrations of ammonium cause a rapid decay of nitrate uptake and nitrate reductase activity. The two activities are differentially inactivated (the uptake activity being more sensitive). Glutamine and asparagine are as effective as NH(4) (+) in suppressing nitrate uptake activity. Glutamate and alanine were about half as effective as NH(4) (+). Cycloheximide interferes with the NH(4) (+)-induced decay of nitrate uptake activity. The ammonium transport system is almost maximally deinhibited (or derepressed) in nitrate-grown mycelium.
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PMID:Regulation of Nitrate Uptake in Penicillium chrysogenum by Ammonium Ion. 1665 63

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 effects of nitrogen source NO(3) (-) or NH(4) (+) on nitrogen metabolism during the first 2 weeks of germination of the rice seedling (Oryza sativa L., var. IR22) grown in nutrient solution containing 40 mug/ml N were studied. Total, soluble protein, and free amino N levels were higher in the NH(4) (+)-grown seedling, particularly during the 1st week of germination. Asparagine accounted for most of the difference in free amino acid level, in both the root and the shoot. Nitrate and nitrite reductase activities were present mainly in the shoot and were higher in the NO(3) (-)-grown seedling, whereas the activity of glutamate dehydrogenase and glutamine synthetase in the root tended to be lower than that of the NH(4) (+)-grown seedling during the 1st week of germination. Glycolate oxidase and catalase activities were present mainly in the shoot. Maximum activity of the above five enzymes occurred 7 to 10 days after germination. Differences in the zymograms of nitrate reductase, glutamate dehydrogenase, and catalase were mainly between shoot and root and not from N source. Nitrite reductase bands were observed only in plants grown in plants grown in NO(3) (-).Ten-day-old seedlings of three rices differing in level of grain protein did not differ in the level of N fractions and of enzyme activities, which were consistent with their differences in grain protein content.
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PMID:Aspects of nitrogen metabolism in the rice seedling. 1665

When amino acids or ammonia are added to plant systems, the effects on the development of nitrate-dependent nitrate reductase activity are variable. In addition, amino acids added singly or as casein hydrolysate may not support a normal growth. A physiologically correct mixture of amino acids, one similar in composition to amino acids released by the endosperm, has been shown to support normal growth and protein synthesis in corn (Zea mays) embryos. In this investigation, we have used the mixture of corn amino acids to determine whether amino acids have an effect on the appearance or disappearance of nitrate reductase activity. The results show that these amino acids partially inhibit the induction of nitrate reductase in corn roots. The effect is more pronounced in mature root than in root tip sections. When glutamine and asparagine are included along with the "corn amino acid mixture," the inhibition is more severe. Amino acids or amino acid analogues added singly to the induction medium have a similar effect: i.e. when the induction of nitrate reductase is inhibited in the root tips (lysine, canavanine, azaserine, azetidine-2-carboxylic acid, dl-4-azaleucine, asparagine, and glutamine), that inhibition is more severe in mature root sections. Arginine enhanced the recovery of nitrate reductase in root tips but inhibited it in mature root sections. The effect of the amino acids is apparently on some phase of the induction processes (i.e. the uptake or distribution of nitrate or a direct effect on the synthesis of the enzyme) and not on the turnover of the enzyme.
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PMID:Ammonium and amino acids as regulators of nitrate reductase in corn roots. 1665 59

Glycine, asparagine, and glutamine inhibited the induction by nitrate of nitrate reductase activity in root tips of cotton (Gossypium hirsutum L.). This inhibition was partially or entirely prevented when the inhibitor was applied in combination with any of several other amino acids. Studies of (14)C-labeled amino acid uptake showed that, in most cases, the apparent antagonism resulted simply from competition for uptake. However, certain antagonists did not curtail uptake. The most effective of these were leucine (against all three inhibitors), and isoleucine and valine (against asparagine or glutamine, but not glycine). These results show that interactions among amino acids in the regulation of nitrate reductase induction result from at least two mechanisms, one acting on uptake of inhibitory amino acids, and the other involving true antagonism.
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PMID:Amino Acid interactions in the regulation of nitrate reductase induction in cotton root tips. 1666 Jan 16

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

Infection by the fungal endophyte Acremonium coenophialum affected the accumulation of inorganic and organic N in leaf blades and leaf sheaths of KY 31 tall fescue (Festuca arundinacea Schreb.) grown under greenhouse conditions. Total soluble amino acid concentrations were increased in either the blade or sheath of the leaf from infected plants. A number of amino acids were significantly increased in the sheath, but only asparagine increased in the blade. Infection resulted in higher sheath NH(4) (+) concentrations, whereas NO(3) (-) concentrations decreased in both leaf parts. The effects on amino acid, NO(3) (-), and NH(4) (+) concentrations were dependent upon the level of N fertilization and were usually apparent only at the high rate (10 millimolar) of application. Administration of (14)CO(2) to the leaf blades increased the accumulation of (14)C in their amino acid fraction but not in the sheaths of infected plants. This may indicate that infection increased amino acid synthesis in the blade but that translocation to the sheath, which is the site of fungal colonization, was not affected. Glutamine synthetase activity was greater in leaf blades of infected plants at high and low N rates of fertilization, but nitrate reductase activity was not affected in either part of the leaf. Increased activities of glutamine synthetase together with the other observed changes in N accumulation and metabolism in endophyte-infected tall fescue suggest that NH(4) (+) reassimilation could also be affected in the leaf blade.
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PMID:Effects of the Fungal Endophyte Acremonium coenophialum on Nitrogen Accumulation and Metabolism in Tall Fescue. 1666 41


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