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

Abstract

The rate of destruction of indole-3-acetic acid (called IAA) by a crude enzyme prepn. from etiolated pea epicotyls is increased by 2,4-D. A natural inhibitor present in boiled onion juice opposes this increase. It is here suggested that the enzyme in situ is normally functioning at suboptimal rates which are controlled by a heat-stable inhibitor present in the tissues. Applied 2,4-D counteracts this inhibition, permitting a greater rate of IAA destruction. As there appears to be a dynamic equilibrium between production of IAA from tryptophan (Wildman, Ferri and Bonner, 1947) and its destruction by IAA oxidase, the characteristic effects on plant growth produced by relatively large amts. of 2,4-D might well arise through disturbing this equilibrium.