Metabolism of l-Threonic Acid in Rumex x acutus L. and Pelargonium crispum (L.) L'Hér

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Abstract
L-Threonic acid is a natural constituent in leaves of P. crispum (L.) L''Her (lemon geranium) and Rumex acutus L. (sorrel). In both species, L-[14C]threonate is formed after feeding L-[U-14C]ascorbic acid to detached leaves. R. acutus leaves labeled with L-[4-3H]- or L-[6-3H]ascorbic acid produce L-[3H]threonate, in the 1st case internally labeled and in the 2nd case confined to the hydroxymethyl group. These results are consistent with the formation of L-threonate from C 3-6 of L-ascorbic acid. Detached leaves of P. crispum oxidize L-[U-14C]threonate to L-[14C]tartrate whereas leaves of R. acutus produce negligible tartrate and the bulk of the 14C appears in 14CO2, [14C]sucrose and other products of carbohydrate metabolism. R. acutus leaves that are labeled with L-[U-14C]threonate release 14CO2 at a linear rate until a limiting value of 25% of the total [U-14C]threonate is metabolized. A small quantity of [14C]glycerate is produced which suggests a process involving decarboxylation of L-[U-14C]threonate.