Proline Content and Metabolism during Rehydration of Wilted Excised Leaves in the Dark

Excised bean (Phaseolus vulgaris) leaves were used to measure changes in proline content and proline metabolism during rehydration in the dark after the leaves had been incubated in the dark 24 hours in a wilted condition.The increase in nonprotein proline which occurs in wilted leaves stopped immediately upon rehydration, and thereafter levels of proline declined. The rate of decline and the fate of the metabolized proline depended on the amount of carbohydrate present. When the level of carbohydrate was relatively high, the rate of decline in proline content was slow, and the proline was converted mainly to protein proline. When the level of carbohydrate was relatively low, the rate of proline decline was rapid and a large percentage of the proline was oxidized to CO(2) and other amino acids in addition to conversion to protein proline.The results indicate that nonprotein proline can be oxidized when the level is increased by endogenous synthesis. Proline oxidation has been observed when the levels are increased by adding exogenous proline. Oxidation of endogenous proline is inhibited by carbohydrates in the leaf, as is true of oxidation of exogenous proline.