Metabolism of 2,4-Dichlorophenoxyacetic Acid. III. Metabolism and Persistence in Dormant Plant Tissue.

In contrast to actively growing, susceptible plants which usually respond very promptly to applied 2,4dichlorophenoxyacetic acid (2,4-D), certain perennials that have been treated toward the end of a growing season may not exhibit morphological responses until the following season (9, 10, 12, 13). It has been a moot question whether (a) such delayed responses are initiated in sensitive cells of winter buds at time of application of the growth-regulator but become visible only much later when the buds renew development or (b) 2,4-D, or some physiologically active product thereof, persists in the dormant plant and interacts the following season with tissues which become sensitive as they renew development (2, 3, 11, 13, 14). Previous experiments with C14-labeled 2,4-D have furnished direct evidence of relatively long persistence of the compound in bean plants. Although a portion of the applied growth-regulator is rapidly transformed into a variety of products (5, 15, 16), a significant amount may remain unaltered for at least 42 days (6). Less direct evidence of persistence of an active growth-regulator has been provided also by observations of protracted morphological responses in cotton (4, 7, 8) and of long delayed fruit abscission in apple (10). In these instances it has not been established whether the delayed or protracted responses are due to 2,4-D itself or to a biologically active transformation product. The present experiment was undertaken with the objective of obtaining direct information concerning the metabolism and persistence of 2,4-D in dormant buds.