l-Ascorbic Acid Metabolism in Vitaceae: Conversion to (+)-Tartaric Acid and Hexoses.

The metabolic fate of l-ascorbic acid-1-(14)C and -6-(14)C has been investigated in two species in two genera of Vitaceae. Results suggest that ascorbic acid metabolism in the Vitaceae involves splitting the 6-carbon chain into 4- and 2-carbon fragments. The former, corresponding to C1 through C4 of ascorbic acid, is further oxidized to tartaric acid while the latter, corresponding to C5 and C6, is recycled into hexose phosphate metabolism. Comparison of these findings with previous observations on the conversion of ascorbic acid to (+)-tartaric acid in Pelargonium crispum clearly reveals two distinct processes of tartaric acid biosynthesis in those plants identified as tartaric acid accumulators.