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Carbon and nitrogen partitioning in young nodulated pea (wild type and nitrate reductase‐deficient mutant) plants exposed to NH 4 NO 3
Author(s) -
Taylor David C.,
Shelp Barry J.,
Nelson Louise M.,
Grodzinski Bernard
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.tb02023.x
Subject(s) - nitrogenase , nitrogen fixation , nitrite reductase , rhizobium , pisum , legume , rhizobium leguminosarum , leghemoglobin , nitrate reductase , nitrite , nitrate , biology , symbiosis , nitrogen assimilation , nitrogen , biochemistry , botany , asparagine , amino acid , root nodule , chemistry , rhizobiaceae , horticulture , inoculation , bacteria , enzyme , ecology , genetics , organic chemistry
Carbon and nitrogen partitioning was examined in a wild‐type and a nitrate reductase‐deficient mutant (A317) of Pisum sativum L. (ev. Juneau), effectively inoculated with two strains of Rhizobium leguminosarum (128C23 and 128C54) and grown hydroponically in medium without nitrogen for 21 days, followed by a further 7 days in medium without and with 5 mM NH 4 NO 3 . In wild‐type symbioses the application of NH 4 NO 3 significantly reduced nodule growth, nitrogenase (EC 1.7.99.2) activity, nodule carbohydrates (soluble sugars and starch) and allocation of [ 14 C]‐labelled (NO 3 − , NH 4 + , amino acids) in roots. In nodules, there was a decline in amino acids together with an increase in inorganic nitrogen concentration. In contrast, symbioses involving A317 exhibited no change in nitrogenase activity or nodule carbohydrates, and the concentrations of all nitrogenous solutes measured (including asparagine) in roots and nodules were enhanced. Photosynthate allocation to the nodule was reduced in the 128C23 symbiosis. Nitrite accumulation was not detected in any case. These data cannot be wholly explained by either the carbohydrate deprivation hypothesis or the nitrite hypothesis for the inhibition of symbiotic nitrogen fixation by combined nitrogen. Our result with A317 also provided evidence against the hypothesis that NO 3 − and NH 4 + or its assimilation products exert a direct effect on nitrogenase activity. It is concluded that more than one legume host and Rhizobium strain must be studied before generalizations about Rhizobium /legume interactions are made.