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

The biosynthetic conversion of D-glucose to tartaric acid (TA)was studied in attached leaves and berries of Vitis labruscacv. Delaware (grape), and in leaves of Parthenocissus quinquefoliaL. (Virginia creeper) under light or dark conditions. D-2-¹⁴C,3-³H]glucose was supplied for a period of 12 h and the ratioof ³H to ¹⁴C in cell wall-derived glucosyl units and TA wasexamined. TA produced via L-ascorbic acid (AA) should lose 3Hduring this conversion while TA produced via D-gluconate shouldretain ³H. In the light, approximately 85 to 91% of the TA presentin grapes and 98% of the TA present in Virginia creeper appearedto be generated via the pathway that involves AA. In the dark,approximately 69 to 74% of the TA in grapes and 87% of the TAin Virginia creeper was synthesized via the AA pathway. When0.5% unlabeled AA was present in the solution of labeled D-glucosethat was supplied to attached leaves of Virginia creeper, agreater proportion of TA was produced via the non-AA pathway.Similarly, detached Virginia creeper leaves produced a greaterproportion of TA via the non-AA pathway. These studies indicatethat vitaceous plants utilize the AA-inclusive pathway to producea major portion of their TA, especially in the light. The valueof P. quinquefolia as a useful model for year-round study ofthe biosynthesis of AA and TA is also discussed. (Received January 23, 1989; Accepted June 19, 1989)