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)

Nitrate reductase (NR; EC 1.6.6.1) is the first enzyme of the nitrate-assimilatory pathway and is regulated transcriptionally and post-translationally by several metabolic and environmental signals. To investigate whether NR is controlled by the rate of photosynthetic CO2 assimilation in cucumber (Cucumis sastivus L.), intact plants were exposed, after the dark period, to light under different atmospheric CO2 concentrations (100, 400 and 2,000 microL x L(-1)) for 2 h. The in-vivo rates of net CO2 assimilation correlated with atmospheric CO2 concentrations. The CO2-fixation rate under 2,000 microL x L(-1) CO2 was 2.4- and 5.4-fold higher than under 400 and 100 microL x L(-1), respectively. Stomatal conductances and transpiration rates were almost identical after the 2-h light period under the various CO2 concentrations tested. Increasing atmospheric CO2 concentrations caused concomitant increases in the contents of starch and soluble sugars in the leaves and a decrease in the nitrate content. The activity and activation state of NR were both higher under elevated CO2 than under low CO2. High CO2 also enhanced NR-gene expression in the leaves. Sugars were supplied via roots to intact carbohydrate-starved plants and NR mRNA levels were analysed after 7 h. Fructose markedly stimulated NR-gene transcription in both leaves and roots. It is concluded that, in cucumber plants, the rate of CO2 assimilation controls the rate of nitrate assimilation by modulation of NR expression and activity, and that sugars are presumably involved as regulatory metabolites.
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PMID:A short-term exposure of cucumber plants to rising atmospheric CO2 increases leaf carbohydrate content and enhances nitrate reductase expression and activity. 1121 52

Fructose 2,6-bisphosphate (fru-2,6-P2) is a signalling metabolite that regulates photosynthetic carbon partitioning in plants. The content of fru-2,6-P2 in Arabidopsis leaves varied in response to photosynthetic activity with an abrupt decrease at the start of the photoperiod, gradual increase through the day, and modest decrease at the start of the dark period. In Arabidopsis suspension cells, fru-2,6-P2 content increased in response to an unknown signal upon transfer to fresh culture medium. This increase was blocked by either 2-deoxyglucose or the protein phosphatase inhibitor, calyculin A, and the effects of calyculin A were counteracted by the general protein kinase inhibitor K252a. The changes in fru-2,6-P2 at the start of dark period in leaves and in the cell experiments generally paralleled changes in nitrate reductase (NR) activity. NR is inhibited by protein phosphorylation and binding to 14-3-3 proteins, raising the question of whether fructose-6-phosphate,2-kinase/fructose-2,6-bisphosphatase protein from Arabidopsis thaliana (AtF2KP), which both generates and hydrolyses fru-2,6-P2, is also regulated by phosphorylation and 14-3-3s. Consistent with this hypothesis, AtF2KP and NR from Arabidopsis cell extracts bound to a 14-3-3 column, and were eluted specifically by a synthetic 14-3-3-binding phosphopeptide (ARAApSAPA). 14-3-3s co-precipitated with recombinant glutathione S-transferase (GST)-AtF2KP that had been incubated with Arabidopsis cell extracts in the presence of Mg-ATP. 14-3-3s bound directly to GST-AtF2KP that had been phosphorylated on Ser220 (SLSASGpSFR) and Ser303 (RLVKSLpSASSF) by recombinant Arabidopsis calcium-dependent protein kinase isoform 3 (CPK3), or on Ser303 by rat liver mammalian AMP-activated protein kinase (AMPK; homologue of plant SNF-1 related protein kinases (SnRKs)) or an Arabidopsis cell extract. We have failed to find any direct effect of 14-3-3s on the F2KP activity in vitro to date. Nevertheless, our findings indicate the possibility that 14-3-3 binding to SnRK1-phosphorylated sites on NR and F2KP may regulate both nitrate assimilation and sucrose/starch partitioning in leaves.
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PMID:Phosphorylation and 14-3-3 binding of Arabidopsis 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. 1487 7