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Nitrate and nitrite reduction in the plant fraction of alfalfa root nodules
Author(s) -
Becana M.,
AparicioTejo P. M.,
SanchezDiaz M.
Publication year - 1985
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.1399-3054.1985.tb02380.x
Subject(s) - cytosol , nitrate reductase , nitrite , nitrite reductase , nitrate , biochemistry , chemistry , root nodule , reductase , medicago sativa , enzyme , biology , botany , nitrogen , nitrogen fixation , organic chemistry
The plant fraction of alfalfa ( Medicago sativa L. cv. Aragon) nodules contained both nitrate reductase (NR) and nitrite reductase (NiR). Specific activity of NADH‐NR from the cytosol of nodules not treated with NO 3 ‐ was about 30 nmol (mg protein) ‐1‐ h ‐1 and was not basically affected by NO 3 addition. In contrast, typical specific activity for cytosolic NiR was 1.5 umol (mg protein) ‐1 h ‐1 using methyl viologen as electron donor. This activity strongly increased with NO 3 concentration, probably due to substrate induction. Maximal activity was 3.5 μmol (mg protein) ‐1 h ‐1 at 50 to 200 mM NO 3 . Estimates indicate that the contribution of cytosol to the overall NR and NiR activities of alfalfa nodules is distinctly different: less than 10% and about 70%, respectively. The increasing amounts of NO 2 accumulating in the cytosol upon NO 3 , supply, and the different response to NO 3 of bacteroid and cytosolic NRs support the concept that most of this NO 2 comes from the bacteroids.