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Effect of nitrate on nitrogen fixation and nodule carbohydrate and organic acid concentrations in pea mutants deficient in nitrate reductase
Author(s) -
Nelson Louise M.,
Edie Scott A.
Publication year - 1988
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.1399-3054.1988.tb05437.x
Subject(s) - nitrate reductase , pisum , rhizobium leguminosarum , nitrogen fixation , biology , sativum , nitrogen assimilation , leghemoglobin , mutant , botany , rhizobium , nitrate , biochemistry , rhizobiaceae , potassium nitrate , diazotroph , horticulture , inoculation , root nodule , symbiosis , bacteria , enzyme , chemistry , potassium , gene , genetics , ecology , organic chemistry
Nitrate inhibits symbiotic N 2 fixation and a number of hypotheses concerned with NO 3 − assimilation have been suggested to explain this inhibition. These hypotheses were tested using a pea ( Pisum sativum L. cv. Juneau) with normal nitrate reductase NR; (EC 1,6,6,4) activity and two mutants of cv. Juneau, A317 and A334, with impaired NR activity. The plants were inoculated with three strains of Rhizobium leguminosarum and grown for 3 weeks in N‐free medium, followed by 1 week in medium supplemented with 0, 5 or 10 m M KNO 3 before harvesting. NO 3 was taken up at comparable rates by the parent and the mutants and accumulated in leaf and stem tissue of the latter. Acetylene reduction rates were inhibited similarly in both the parent and mutants in the presence of KNO 3 but there were differences among rhizobial strains. Starch concentration of the nodules decreased by 46% in the presence of KNO 3 and there were differences among rhizobial strains but not among pea genotypes. Malate and succinate accumulated in nodules in the presence of KNO 3 . These data are not consistent with the photosynthate deprivation hypothesis as a primary mechanism for NO 3 inhibition of N 2 fixation since NO 3 affected the nodule carbohydrate composition of all three pea genotypes in a similar manner. The lack of correlation between NR activity and NO 3 inhibition of N 2 fixation suggests that NO 3 assimilation may be only indirectly involved in the inhibition phenomenon.