| Popis: |
Summary Incorporation of radiocarbon from L-ascorbic acid-1- 14 C into L-tartaric acid in developing grapevine leaves was found to follow a time-course pattern indicating a consecutive formation of 2-keto-L-idonic, L-idonic, and 5-keto-D-gluconic (= 5-keto-L-idonic) acids. In mature leaves, tartrate synthesis is almost completely interrupted at the oxidative reaction metabolizing Lidonic acid, which consequently accumulates. A series of 14 C0 2 and sucrose-U- 14 C precursor experiments yielded intermediary kinetics with respect to ascorbate and its derivatives, which are consistent with the radiocarbon distribution obtained after administering L-ascorbic acid-1 14 C to tartrate synthesizing material. On the basis of this evidence and the observation that virtually constant 14 C-dilution ratios prevail between ascorbate and tartrate at the time of tracer appearance in the product, it is concluded that L-ascorbic acid represents a genuine and physiological intermediate in L-tartaric acid biosynthesis of vitaceous plants. |
