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

---

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

To investigate nitrogen assimilation and translocation in Zea mays L. colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thax. sensu Gerd.), we measured key enzyme activities, 15N incorporation into free amino acids, and 15N translocation from roots to shoots. Glutamine synthetase and nitrate reductase activities were increased in both roots and shoots compared with control plants, and glutamate dehydrogenase activity increased in roots only. In the presence of [15N]ammonium, glutamine amide was the most heavily labeled product. More label was incorporated into amino acids in VAM plants. The kinetics of 15N labeling and effects of methionine sulfoximine on distribution of 15N-labeled products were entirely consistent with the operation of the glutamate synthase cycle. No evidence was found for ammonium assimilation via glutamate dehydrogenase. 15N translocation from roots to shoots through the xylem was higher in VAM plants compared with control plants. These results establish that, in maize, VAM fungi increase ammonium assimilation, glutamine production, and xylem nitrogen translocation. Unlike some ectomycorrhizal fungi, VAM fungi do not appear to alter the pathway of ammonium assimilation in roots of their hosts.
...
PMID:Ammonia Assimilation in Zea mays L. Infected with a Vesicular-Arbuscular Mycorrhizal Fungus Glomus fasciculatum. 1223 37

AREA (NIT2) is a general transcription factor involved in derepression of numerous genes responsible for nitrogen utilization in Gibberella fujikuroi and many other fungi. We have previously shown that the deletion of areA-GF resulted in mutants with significantly reduced gibberellin (GA) production. Here we demonstrate that the expression level of six of the seven GA biosynthesis genes is drastically reduced in mutants lacking areA. Furthermore, we show that, despite the fact that GAs are nitrogen-free diterpenoid compounds, which are not obviously involved in nitrogen metabolism, AREA binds directly to the promoters of the six N-regulated genes. The binding of AREA was analysed in more detail using the promoter of one of the GA-biosynthesis genes encoding the ent-kaurene oxidase (P450-4). Deletion/mutation analysis of the P450-4 promoter fused to the Escherichia coli uidA gene, which encodes beta-glucuronidase, allowed the in vivo identification of functional GATA motifs. We have also analysed the nmr gene of G. fujikuroi (nmr-GF) which has high similarity to the Neurospora crassa nmr-1 and Aspergillus nidulans nmrA genes, both involved in nitrogen metabolite repression. In contrast to our expectation, deletion of nmr-GF did not result in significant derepression of the GA biosynthesis genes in the presence of ammonium, glutamine or glutamate. Overexpression of the nmr-GF gene fused to the strong promoter of the G. fujikuroi glutamine synthetase (gs) gene revealed only a very slight repression of the nitrate reductase (niaD) gene, resulting in weak resistance to chlorate. Surprisingly, this effect was only observed in the presence of high amounts of glutamate; cultivation on ammonium failed to induce any resistance to chlorate. Despite the limited effect of gene replacement and overexpression of nmr-GF on the nitrogen metabolism of G. fujikuroi itself, the gene fully restored nitrogen metabolite repression in A. nidulans and N. crassa nmr mutants. Therefore, we postulate that, in contrast to A. nidulans and N. crassa, NMR does not function independently as the main modulator of AREA in G. fujikuroi.
...
PMID:AREA directly mediates nitrogen regulation of gibberellin biosynthesis in Gibberella fujikuroi, but its activity is not affected by NMR. 1258 53

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.
...
PMID:Characterization of the Tuber borchii nitrate reductase gene and its role in ectomycorrhizae. 1289 21

The role of nitrate reductase (NR) in the regulation of the nitrate assimilation pathway was evaluated in the yeast Hansenula polymorpha. Posttranscriptional regulation of NR in response to reduced nitrogen sources and the effect of a heterologous NR on the transcriptional regulation of nitrate-assimilatory gene expression was examined. The strain bearing YNR1 (nitrate reductase gene) under the control of the methanol-induced MOX (methanol oxidase) promoter showed that NR is active in the presence of reduced nitrogen sources. In cells incubated with glutamine plus nitrate, rapamycin abolished nitrogen catabolite repression, NR activity being very similar to that in cells induced by nitrate alone. This reveals the involvement of the Tor-signalling pathway in the transcriptional regulation of H. polymorpha nitrate assimilation genes. To assess the role of NR in nitrate-assimilatory gene expression, different strains lacking YNR1, or both YNR1 and YNT1 (high-affinity nitrate transporter) genes, or expressing the tobacco NR under the YNR1 promoter, were used. Tobacco NR abolished the constitutive nitrate-assimilatory gene induction shown by an NR gene disruptant strain. Moreover, in strains lacking the high-affinity nitrate transporter and NR this deregulation disappeared. These facts discard the role of NR protein in the transcriptional induction of the nitrate-assimilatory genes and point out the involvement of the high-affinity nitrate transporter as a part of the nitrate-signalling pathway.
...
PMID:The role of nitrate reductase in the regulation of the nitrate assimilation pathway in the yeast Hansenula polymorpha. 1461 79

The capacity for nitrate reduction, as measured by nitrate reductase activity (NRA), was generally low for a range of plant communities in Australia (coastal heathland, rainforest, savanna woodland, monsoon forest, mangrove, open Eucalyptus forest, coral cay open forest) and only a loose relationship existed between NRA and leaf nitrogen concentration. This suggests that nitrate ions are not the sole nitrogen source in these communities. Based on (15)N labeling experiments, we found a range of tree species exhibiting a pronounced preference for uptake of ammonium over nitrate. Analysis of soil solutions from several forest and heathland communities indicated that ammonium ions were more prevalent than nitrate ions and that soluble forms of organic nitrogen (amino acids and protein) were present in concentrations similar to those of mineral nitrogen. To determine the extent to which root adaptations and associations might broaden nitrogen source utilization to include organic nitrogen, we assessed the effects of various nitrogen sources on seedling growth in sterile culture. Non-mycorrhizal seedlings of Eucalyptus grandis W. Hill ex Maiden and Eucalyptus maculata Hook. grew well on mineral sources of nitrogen, but did not grow on organic sources of nitrogen other than glutamine. Mycorrhizal seedlings grew well on a range of organic nitrogen sources. When offered a mixture of inorganic and organic nitrogen sources at low concentrations, mycorrhizal seedlings derived a significant proportion of their nitrogen budget from organic sources. We also demonstrated that a species of the obligately non-mycorrhizal genus Hakea, a heathland proteaceous shrub possessing cluster roots, had the ability to incorporate (15)N-labeled organic sources (e.g., glycine). We conclude that mycorrhizal associations and root adaptations confer the ability to substantially broaden the nitrogen source base on some plant species.
...
PMID:Root adaptation and nitrogen source acquisition in natural ecosystems. 1487 87

Ynt1 is the only high-affinity nitrate uptake system in Hansenula polymorpha. Nitrate uptake was directly correlated with the Ynt1 levels and shown to be independent of nitrate reductase (NR) activity levels. Ynt1 failed to transport chlorate and, as a result, strains lacking YNT1 were sensitive to chlorate, as is the wild-type. Nitrite uptake in a wild-type strain was partially inhibited by nitrate to levels shown by a YNT1-disrupted strain in which, in turn, nitrite transport was not inhibited by nitrate. It is concluded that nitrite uptake takes place by two different transport systems: Ynt1 and a nitrite-specific transporter(s). The nitrite-specific transport system was induced by nitrate; consistently, no induction was observed in strains lacking the transcription factor YNA1, which is involved in nitrate and nitrite induction of the nitrate assimilatory structural genes. Ynt1 presents its optimal rate for nitrite uptake at pH 6, while pH 4 was optimal for the specific nitrite uptake system(s). At pH 5.5, the contribution of Ynt1 to high-affinity nitrate and nitrite uptake was around 95% and 60%, respectively. The apparent Km of Ynt1 for nitrate and nitrite is in the microM range, as is the specific nitrite uptake system for nitrite. The analysis of the effect of the reduced nitrogen sources on nitrate assimilation revealed that glutamine inactivates nitrate and nitrite transport, dependent on Ynt1, but not the nitrite-specific system.
...
PMID:The role of Ynt1 in nitrate and nitrite transport in the yeast Hansenula polymorpha. 1496 31

The Neurospora crassa genome database was searched for sequence similarity to crnA, a nitrate transporter in Aspergillus nidulans. A 3.9-kb fragment (contig 3.416, subsequence 183190-187090) was cloned by PCR. The gene coding for this nitrate transporter was termed nit-10. The nit-10 gene specifies a predicted polypeptide containing 541 amino acids with a molecular mass of 57 kDa. In contrast to crnA, which is clustered together with niaD, encoding nitrate reductase, and niiA, encoding nitrite reductase, nit-10 is not linked to nit-3 (nitrate reductase), nit-6 (nitrite reductase), or to nit-2, nit-4 (both are positive regulators of nit-3), or nmr (negative regulator of nit-3) in Neurospora crassa. A nit-10 rip mutant failed to grow in the medium when nitrate (< 10 mM) was used as the sole nitrogen source, but grew similarly to wild type when nitrate concentration was 10 mM or higher. In addition, it showed strong sensitivity to cesium in the presence of nitrate and resistance to chlorate in the presence of alanine, proline, or hypoxanthine. The expression of nit-10 required nitrate induction and was subject to repression by nitrogen metabolites such as glutamine. Expression of nit-10 also required functional products of nit-2 and nit-4. The half-life of nit-10 mRNA was determined to be approximately 2.5 min.
...
PMID:Identification and characterization of a nitrate transporter gene in Neurospora crassa. 1506 36

The niiA (nitrite reductase) and niaD (nitrate reductase) genes of Aspergillus nidulans are subject to both induction by nitrate and repression by ammonium or glutamine. The intergenic region between these genes functions as a bidirectional promoter. In this region, nucleosomes are positioned under nonexpression conditions. On nitrate induction under derepressing conditions, total loss of positioning occurs. This is independent of transcription and of the NirA-specific transcription factor but absolutely dependent on the wide-domain GATA-binding AreA factor. We show here that a 3-amino-acid deletion in the basic carboxy-terminal sequence of the DNA-binding domain results in a protein with paradoxical properties. Its weak DNA binding is consistent with its loss-of-function phenotype on most nitrogen sources. However, it results in constitutive expression and superinducibility of niiA and niaD. Nucleosome loss of positioning is also constitutive. The mutation partially suppresses null mutations in the transcription factor NirA. AreA binds NirA in vitro, and the mutation does not affect this interaction. The in vivo methylation pattern of the promoter is drastically altered, suggesting the recruitment of one or more unknown transcription factors and/or a local distortion on the DNA double helix.
...
PMID:A paradoxical mutant GATA factor. 1507 69

Aseptically grown spruce seedlings were cultivated in a hydroponic system, where the roots were separated from the shoots by a gastight, silicone material. The plants were fumigated with four SO(2) concentrations (93, 190, 270 and 530 microg m(-3)) for nine weeks. Up to 270 microg m(-3) of SO(2), an inhibition of nitrogen metabolism (enzyme activities of nitrate reductase (NR) and glutamine sythetase (GS) and nitrate content) in the shoot was compensated by a stimulation in the root, while nitrogen uptake was unaffected. Only the treatment with 530 microg m(-3) of SO(3) decreased enzyme activities, nitrate content in both roots and shoots as well as nitrate uptake, and inhibited the growth of plants. Increases in the content of thiols and superoxidismutase activity are discussed in terms of SO(2) detoxification.
...
PMID:The effects of SO2 fumigation on the nitrogen metabolism of aseptically grown spruce seedlings. 1509 43

We investigated the physiological consequences for nitrogen metabolism and growth of the deregulated expression of an N-terminal-deleted tobacco nitrate reductase in two lines of potato (Solanum tuberosum L. cv Safrane). The transgenic plants showed a higher biomass accumulation, especially in tubers, but a constant nitrogen content per plant. This implies that the transformed lines had a reduced nitrogen concentration per unit of dry weight. A severe reduction in nitrate concentrations was also observed in all organs, but was more apparent in tubers where nitrate was almost undetectable in the transgenic lines. In leaves and roots, but not tubers, this nitrate decrease was accompanied by a statistically significant increase in the level of malate, which acts as a counter-anion for nitrate reduction. Apart from glutamine in tubers, no major changes in amino acid concentration were seen in leaves, roots or tubers. We conclude that enhancement of nitrate reduction rate leads to higher biomass production, probably by allowing a better allocation of N-resources to photosynthesis and C-metabolism.
...
PMID:Expression of a deregulated tobacco nitrate reductase gene in potato increases biomass production and decreases nitrate concentration in all organs. 1519 93


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---