On the Mechanism of Action of 2, 4-Dichlorophenoxyacetic Acid

Abstract

The use of synthetic plant growth-regulating compounds is of increasing economic importance in agriculture but little is known of their fundamental mechanism of action. The hormone-like character and general structural similarity of certain substituted aryl-acetates and -oxyacetates or their potential precursors (Zimmerman and Hitchcock 1941-42) to that of indole-3-acetic acid (LA.A.) suggest that these compounds may act indirectly by altering the activity of this natural plant hormone. Tang and Bonner (1947) have partially characterized an enzyme prepared from pea epicotyls (and referred to here as LA.A. oxidase) which oxidizes and inactivates LA.A. On adding 11 auxin analogues to a crude enzyme preparation they found no change in the rate of LA.A. inactivation. However, as these workers used a substrate (LA.A.) concentration that was rate-limiting, the only rate-change necessarily to be detected would have been a decrease due to competition with the substrate.