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Effects of water stress on enzymes of ammonia assimilation in root nodules of alfalfa ( Medicago sativa )
Author(s) -
Becana M.,
AparicioTejo P. M.,
SánchezDíaz M.
Publication year - 1984
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1984.tb05186.x
Subject(s) - glutamate synthase , glutamate dehydrogenase , glutamine synthetase , biochemistry , nad+ kinase , biology , glutamine , root nodule , enzyme , glutamate receptor , nitrogen fixation , amino acid , bacteria , genetics , receptor
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 N 2 ‐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.