Changes in Amino Acid Content of Excised Leaves During Incubation. III. Role of Sugar in the Accumulation of Proline in Wilted Leaves.

A previously reported accumulation of proline in wilted turnip leaves has been observed in 6 additional species representing 5 different families. The results of experiments on the conditions affecting the behavior of proline in wilted leaves were interpreted to mean that the supply and metabolism of available carbohydrate was essential for proline accumulation.The role of sugar in proline accumulation was determined by incubating wilted leaves with different levels of carbohydrate (produced either by variations in conditions of preillumination or by infiltration with sucrose). The results showed that proline accumulation was greater and most prolonged in wilted leaves with higher sugar and starch contents. No proline accumulation was observed in unwilted leaves. Also some inhibitors of glycolysis and of the tricarboxylic acid cycle prevented proline accumulation in wilted leaves.Based on these results, the interpretation of the role of sugar in proline accumulation is that the oxidation of sugars furnishes alpha-ketoglutarate and NAD(P)H for proline synthesis in wilted leaves.