de Marco A, Jia C, Fischer-Sehliebs E, Varanini Z, Lüttge U. Evidence for two different nitrate-reducing activities at the plasma membrane in roots of Zea mays L.
PLANTA 1994;
194:557-564. [PMID:
24624488 DOI:
10.1007/bf00714470]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Plasma-membrane (PM) vesicles isolated from 6-d-old corn roots by sucrose gradient centrifugation or two-phase partitioning showed an NADH-dependent nitrate reductase (NR) activity averaging at 40 nmol per milligram PM protein per hour. This membrane-associated NR activity could not be removed from two-phase partitioned PM vesicles by salt washing, osmotic shock treatment, sonication, or freeze-thawing to reverse vesicle sidedness. Therefore, it could not be attributed to contamination of membrane vesicles by the soluble, cytosolic NR. Plasma-membrane vesicles reduced NO~ in the presence of the electron donors NADH or NADPH at an activity ratio of 2.2. The NADH- and NADPH-dependent NR activities of outside-out oriented PM vesicles differed in their sensitivity toward the detergent Brij 58,leading to a latency of 65% or 29% using NADH or NADPH as electron donor, respectively. The activities of NO 3 reduction in the presence of saturating concentrations of NADH and NADPH were additive. Furthermore,both activities were characterized by a different pH dependence with a pH optimum of 7.5 for the NADH-dependent activity and of 6.8 for the NADPH-dependent activity. The membrane-associated NAD(P)H-dependent NR activities responded to different nitrogen nutrition of plants in a manner different from the soluble forms of the enzyme. The data confirm the existence of a corn PM NR and suggest that there may be two different NO₃-reducing enzymes located at the PM of corn roots.
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