Studies on l-ascorbic acid biosynthesis and metabolism in Parthenocissus quinquefolia L. (vitaceae) |
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Authors: | Johannes PFG Helsper Frank A Loewus |
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Institution: | 1. Department of Botany, Catholic University of Nijmegen, Toernooiveld, 6525 ED Nijmegen The Netherlands;2. Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340 U.S.A. |
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Abstract: | Parthenocissus quinquefolia (L.) Planch., commonly known as Virginia Creeper, is a vitaceous tartrate-accumulating vine that exhibits C-4/C-5 cleavage of l-ascorbic acid (AA) to produce l-tartaric acid (TA) from the C4 fragment and carbohydrate pool material from the C2 fragment. Experiments in which detached leaves were supplied d-5-3H,1-14C]glucose or d-5-3H,6-14C]glucose yielded AA devoid of 3H whereas the l-threonic acid (ThA) and TA recovered from the same tissues still retained some 3H. These comparative experiments also indicated that the ThA was derived from carbons 3 through 6 of d-glucose. ThA was shown to be a natural constituent of P. quinquefolia but apparently not an intermediate between AA and TA. Results are consistent with a biosynthetic pathway from d-glucose to AA that involves a hydrogen-exchanging epimerization at C-5 as reported earlier for the geraniaceous plant Pelargonium crispum, but differing from P.crispum in biosynthesis and metabolism of ThA.When l-6-14C]idonate or its lactone was supplied to P. quinquefolia leaves, about 80% of the 14C appeared in the carbohydrates, an observation remarkably similar to previous observations with 6-14C]AA-labeled leaves. l-Idonate and its lactone appear to have an intermediate role in AA metabolism in vitaceous plants. |
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Keywords: | AA Glc IA 5-keto IA ThA TA |
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