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

The reduction of dehydroascorbate (DHA) was investigated in plant mitochondria. Mitochondria isolated from Bright Yellow-2 tobacco cells were incubated with 1 mM 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.