Transgenic tobacco plants that overexpress alfalfa NADH‐glutamate synthase have higher carbon and nitrogen content
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This work reports the characterization of transgenic tobacco (Nicotiana tabacum L.) plants that constitutively overexpress NADH‐GOGAT. Three independent transformants, designated GOS10, GOS13 and GOS19 (for GOGAT sense), with stable integration of the chimeric alfalfa NADH‐GOGAT gene fused to the CaMV 35S promoter were studied. The transgene was stably integrated and inherited by the progeny. In these GOS lines, the expression of NADH‐GOGAT mRNA and protein was detected at low levels in roots and leaves, while the expression of the host tobacco NADH‐GOGAT gene was nearly undetectable. The roots of GOS lines showed an elevated (15–40%) enzyme activity as compared to control plants. When GOS plants were grown under greenhouse conditions and fed with either nitrate or ammonium as the sole nitrogen source, they showed higher total carbon and nitrogen content in shoots and increased shoot dry weight when plants were entering into the flowering stage, as compared to control plants. The observed phenotype of GOS plants was interpreted as reflecting a higher capacity to assimilate nitrogen due to a higher NADH‐GOGAT activity.Keywords:
Glutamate synthase
The enzymes involved in the assimilation of ammonia by free-living cultures of Rhizobium spp. are glutamine synthetase (EC. 6.o.I.2), glutamate synthase (L-glutamine:2-oxoglutarate amino transferase) and glutamate dehydrogenase (ED I.4.I.4). Under conditions of ammonia or nitrate limitation in a chemostat the assimilation of ammonia by cultures of R. leguminosarum, R. trifolii and R. japonicum proceeded via glutamine synthetase and glutamate synthase. Under glucose limitation and with an excess of inorganic nitrogen, ammonia was assimilated via glutamate dehydrogenase, neither glutamine synthetase nor glutamate synthase activities being detected in extracts. The coenzyme specificity of glutamate synthase varied according to species, being linked to NADP for the fast-growing R. leguminosarum, R. melitoti, R. phaseoli and R. trifolii but to NAD for the slow-growing R. japonicum and R. lupini. Glutamine synthetase, glutamate synthase and glutamate dehydrogenase activities were assayed in sonicated bacteroid preparations and in the nodule supernatants of Glycine max, Vicia faba, Pisum sativum, Lupinus luteus, Medicago sativa, Phaseolus coccineus and P. vulgaris nodules. All bacteroid preparations, except those from M. sativa and P. coccineus, contained glutamate synthase but substantial activities were found only in Glycine max and Lupinus luteus. The glutamine synthetase activities of bacteroids were low, although high activities were found in all the nodule supernatants. Glutamate dehydrogenase activity was present in all bacteroid samples examined. There was no evidence for the operation of the glutamine synthetase/glutamate synthase system in ammonia assimilation in root nodules, suggesting that ammonia produced by nitrogen fixation in the bacteroid is assimilated by enzymes of the plant system.
Glutamate synthase
Nitrogen Assimilation
Rhizobium leguminosarum
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Aims Nitrogen is very important for improving the yield and quality of peanut. Nitrate reductase (NR), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) are the main enzymes of nitrogen metabolism that would be affected by nitrogen level. Our objective was to study the effects of nitrogen level on soluble protein content, free amino acid content and correlating enzyme activities of nitrogen metabolism in peanut. Methods We carried out a field experiment of two cultivars under four nitrogen levels (0, 45, 90 and 180 N kg·hm–2) and investigated the soluble protein content and free amino acid content in leaf, stem, root and pod of peanut, as well as the activities of the nitrate reductase (NR), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in these organs. Important findings With the nitrogen application, the soluble protein content and free amino acid content were increased, and the activities of the nitrate reductase (NR), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) also increased. When excessive nitrogen was used, the NR activity and kernel protein content were increased, while the activities of GS and GDH were decreased. Soluble protein content, free amino acid content, NR, GS and GDH along with the growth periods were not affected by nitrogen level, but with suitable nitrogen the activities of NR and GS in different organs could be increased. Also, nitrogen level affected GDH activities in leaf and kernel, with lower effect on the GDH activities in stalk and root. In conclusion, nitrogen level could affect the correlating enzyme activities of nitrogen metabolism in peanut, which resulted in changes of soluble protein content and free amino acid content in organs. The best nitrogen level for peanut was 90 N kg·hm–2.
Glutamate synthase
Nitrogen Cycle
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Glutamate synthase
Nitrogen Assimilation
Assimilation (phonology)
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Glutamate synthase
Nitrogen Assimilation
Nitrogen Cycle
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Levels of activity of glutamine synthetase, glutamate dehydrogenase and NADH-dependent glutamate synthase in nodule cytoplasm extracts of twelve herbaceous legume species have been measured. Nodules of all species contained substantial quantities of glutamine synthetase. Levels of glutamate synthase were found to be between 7 and 100% of those of glutamine synthetase, while levels of glutamate dehydrogenase varied widely between 0.2 and 150% of those of glutamine synthetase. The estimated Km for hydroxylamine of glutamine synthetase was found to vary between 0.02 and 0.5 mM in nine species tested, while that of glutamate dehydrogenase for ammonia varied between 0.03 M and 0.1 M in the four species containing significant levels of that enzyme. It is proposed that the pathway of ammonia assimilation via glutamine synthetase and NADH-dependent glutamate synthase-catalysed reactions is universal in legume nodule metabolism.
Glutamate synthase
Nitrogen Assimilation
Hydroxylamine
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The effects of water stress on nitrogen forms,activities of some enzymes related to nitrogen metabolism and photosynthetic properties in rice were studied using a hydroponic experiment.Water stress was caused by adding PEG-6000 into the solution.Slight water stress(PEG≤5%,water potential≥-0.05 MPa) has little effects on contents of amino acid nitrogen,soluble protein and activities of nitrate reductase(NR),glutamine synthetase(GS),glutamate synthase(GOGAT) and glutamate dehydrogenase(GDH),and moreover the absorption and accumulation of nitrate nitrogen are stimulated.However,photosynthetic rate and dry matter accumulation are significantly inhibited.The dry matter accumulation change is significantly correlated with the regulation of photosynthetic rate more than that positive effect of resisting badness effect from environment.Therefore,photosynthetic rate has much more effect on dry matter accumulation than metabolism in vivo of rice.When PEG concentration≥10%(water potential≤-0.15 MPa),the concentrations of different nitrogen forms,some key enzymes of nitrogen metabolism and photosynthetic rate are significantly decreased.These effects on roots under the water stress are significantly larger than those on leaves.The above results indicate concentrations of different nitrogen forms and some key enzymes of nitrogen metabolism and photosynthetic rate are closely related to the intensity of water stress.
Glutamate synthase
Nitrogen Assimilation
Nitrogen Cycle
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Glutamate synthase
Nitrogen Assimilation
Asparagine synthetase
Assimilation (phonology)
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Abstract Young wheat (C3) and maize (C4) plants were exposed to near-ambient concentrations of ozone in open-top chambers in order to investigate the possible effects of ozone on nitrogen metabolism. Nitrogen was supplied to the plants by adding 15N-labelled tracer substances via the soil substrate. Enzyme activities (NADH nitrate reductase, nitrite reductase, glutamine synthetase and NADH glutamate dehydrogenase) and the incorporation of 15N were determined. The findings show that nitrogen metabolism was affected by O3, however, there were distinct differences between the two species. In plants treated with O3, NADH nitrate reductase activity in maize leaves was reduced, while NR activity in wheat leaves only slightly declined. Only minor changes were observed with respect to the activities of nitrite reductase, glutamine synthetase and NADH glutamate dehydrogenase. Feeding experiments using 15NO3 − showed that the incorporation of nitrate nitrogen in wheat plants exposed to ozone remains virtually unchanged, whereas in maize plants reduced incorporation rates were observed for nitrate nitrogen. The incorporation of ammonium nitrogen was distinctly increased in wheat and maize by the impact of ozone. When investigating pigment contents, reduced levels of chlorophyll a and b and carotenoids were observed, whereas the pigment content of wheat leaves remained unchanged. These results indicate that young maize plants are more susceptible than wheat plants to short-term ozone exposure. Key Words: Glutamate dehydrogenaseglutamine synthetasenitrate reductasenitrite reductasenitrogen 15ozonestable isotopes Triticum aestivum Zea mays
Glutamate synthase
Nitrogen Assimilation
Nitrogen Cycle
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Glutamate synthase
Nitrogen Assimilation
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