Proline Accumulation in Tubers of Jerusalem Artichoke

Abstract

When separated whole tubers of Helianthus tuberosus L. were dried, and when tuber slices were plasmolysed in mannitol solutions, free proline accumulated in the tuber tissue. The amount of proline accumulated in tuber slices increased with the concentration of mannitol in the plasmolysing solution. A lag of approximately 24 h preceded proline accumulation in plasmolysed slices. During the lag period, the content of free arginine, a major component of the free amino acid pool, decreased by at least 50%. L-Indospicine, a competitive inhibitor of arginase (L-arginine amidinohydrolase EC 3.5.3.1) inhibited arginine catabolism in slices and also inhibited proline accumulation. On the other hand, cycloheximide, an inhibitor of protein synthesis, did not inhibit arginine loss or proline accumulation. An increase in the concentration of mannitol required for plasmolysis accompanied an increase in free proline in whole, dormant tubers stored at 4°C. These tubers are an example of a non-photosynthetic higher plant tissue in which free proline accumulates when the water potential decreases. The relationship between arginine catabolism and proline accumulation is discussed.