Formation of Tartaric Acid in Vitaceous Plants: Relative Contributions of L-Ascorbic Acid-inclusive and -noninclusive Pathways

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Abstract
The biosynthetic conversion of D-glucose to tartaric acid (TA) was studied in attached leaves and berries of Vitis labrusca cv. Delaware (grape), and in leaves of Parthenocissus quinquefolia L. (Virginia creeper) under light or dark conditions. D-[2-14C, 3-3H]glucose was supplied for a period of 12 h and the ratio of 3H to 14C in cell wall-derived glucosyl units and TA was examined. TA produced via L-ascorbic acid (AA) should lose 3H during this conversion while TA produced via D-gluconate should retain 3H. In the light, approximately 85 to 91% of the TA present in grapes and 98% of the TA present in Virginia creeper appeared to be generated via the pathway that involves AA. In the dark, approximately 69 to 74% of the TA in grapes and 87% of the TA in Virginia creeper was synthesized via the AA pathway. When 0.5% unlabeled AA was present in the solution of labeled D-glucose that was supplied to attached leaves of Virginia creeper, a greater proportion of TA was produced via the non-AA pathway. Similarly, detached Virginia creeper leaves produced a greater proportion of TA via the non-AA pathway. These studies indicate that vitaceous plants utilize the AA-inclusive pathway to produce a major portion of their TA, especially in the light. The value of P. quinquefolia as a useful model for year-round study of the biosynthesis of AA and TA is also discussed.

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