Dehydroascorbate reduction in plant mitochondria is coupled to the respiratory electron transfer chain

Abstract

The reduction of dehydroascorbate (DHA) was investigated in plant mitochondria. Mitochondria isolated from Bright Yellow‐2 tobacco cells were incubated with 1 m M of DHA, and the ascorbate generation was followed by high‐performance liquid chromatography. Mitochondria showed clear ability to reduce DHA and to maintain a significant level of ascorbate. Ascorbate generation could be stimulated by the respiratory substrate succinate. The complex I substrate malate and the complex I inhibitor rotenone had no effect on the ascorbate generation from DHA. Similarly, the complex III inhibitor antimycin A, the alternative oxidase inhibitor salicylhydroxamic acid, and the uncoupling agent 2,4‐dinitrophenol were ineffective on mitochondrial ascorbate generation both in the absence and in the presence of succinate. However, the competitive succinate dehydrogenase inhibitor malonate almost completely abolished the succinate‐dependent increase in ascorbate production. The complex IV inhibitor KCN strongly stimulated ascorbate accumulation. These results together suggest that the mitochondrial respiratory chain of plant cells – presumably complex II – plays important role in the regeneration of ascorbate from its oxidized form, DHA.