Results

Ascorbate, dehydroascorbate (DHA), and glucose transport was investigated in plant mitochondria prepared from cultured BY2 tobacco cells. Using a rapid filtration method, we observed a specific glucose and dehydroascorbate transport, which was temperature and time dependent and saturable. Inhibition of mitochondrial respiration by KCN and the uncoupler 2,4-DNP did not influence the transport of the investigated compounds. The results demonstrate the presence of dehydroascorbate and glucose transport in plant mitochondria and suggest that it is mediated by the same or closely related transporter(s). 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. 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. Invertase activity in the mitochondrial matrix of Helianthus tuberosus tubers was demonstrated. The pH optimum, the kinetic parameters and the inhibitor profile of the invertase activity indicated that it belongs to the neutral invertases. In accordance with this topology, transport activities responsible for the mediation of influx/efflux of substrate/products were shown and characterized.

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