Effects of water stress on enzymes of ammonia assimilation in root nodules of alfalfa (Medicago sativa) |
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Authors: | M Becana P M Aparicio-Tejo M Sánchez-Díaz |
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Institution: | Dpto. de Fisiología Vegetal, Univ. de Navarra, Apartado 273, Pamplona, Spain. |
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Abstract: | Protein content and activities of the enzymes glutamine synthetase (EC 6.3.1.2), NADH-glutamate synthase (EC 1.4.1.14), NADH-glutamate dehydrogenase (reductive amination (EC 1.4.1.2) and NAD+-glutamate dehydrogenase (oxidative deamination) (EC 1.4.1.2) from the plant fraction of root nodules of alfalfa ( Medicago sativa L. cv. Aragon) were determined under water stress. Only NADH-glutamate synthase activity was inhibited during drought. The results indicate that the glutamine synthetase/NADH-glutamate synthase cycle was fully operational in alfalfa nodules of control or even mildly stressed plants when N2-fixation was not inhibited, but that the coupling between glutamine synthetase and NADH-glutamate synthase was lost as drought progressed. Patterns of glutamine synthetase and NADH-/NAD+-gluta-mate dehydrogenase activities reflect changes in ammonia content of nodules and/or availability of carbon substrates, and indicate that nodules maintain sufficient enzyme activity for ammonia assimilation throughout water stress. |
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Keywords: | Glutamate synthase glutamine synthetase NAD+-glutamate dehydrogenase NADH-glutamate dehydrogenase |
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