Dehydroascorbate reductase and function in ascorbate recycling in potatoes

Ascorbate produced by vegetables and fruits is necessary to maintain its antioxidative ability. The enzyme dehydroascorbate reductase (DHAR) is needed to reduce oxidized ascorbate back to its antioxidant-active form. The dhar gene was cloned in the genome of potato cv. Bintje and transformed back into Bintje using the Agrobacterium-mediated T-DNA transfer method. Six putative transformants D1, D2, D4, D5, D6 and D15 were confirmed by PCR and all except D5 were confirmed positive by GUS assay. The gene expression levels of the dhar gene in transformants were 0.7 to 1.94 times different from the wild-type plant. The DHAR enzymatic activity increased in leaves and tubers of D1, D2, D4 and D15. The total and reduced ascorbate contents were increased in leaves of D4 but no change was found in the ratio of oxidized:reduced. The AA, AsA and ratio of oxidized:reduced did not change in the tubers of the transformed plants.