Auxin-stimulated NADH oxidase (semidehydroascorbate reductase) of soybean plasma membrane: Role in acidification of cytoplasm?

Abstract

Purified plasma membrane vesicles isolated both by aqueous twoPhase methods and by free-flow electrophoresis from homogenates prepared in the presence of 10 mM ascorbate, oxidized external NADH at rates of about 15 nanomoles/min/mg protein. The rate in the isolated vesicles was accelerated, without perceptible lag, 1.5-to 2-fold by 1 to 10 μM auxin (2,4-dichlorophenoxyacetic acid or indole-3-acetic acid). The reaction would be expected to result in acidification of the vesicle interiors and is proposed as a mechanism to account for auxin-induced acidification of cytoplasmin vitro.