Kinetics of Growth Inhibition by Herbicides

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Abstract
The growth inhibition of soybean seedlings and yeast cultures, induced by several herbicides and growth substances, was satisfactorily characterized by a kinetic analysis. Single applications of 2,4-D, DCPA, 2,4,5-T, TCA, AT, IAA, and MH on soybeans and of 2,4-D and IAA on yeast cultures, supported the hypothesis that: (1) The plant growth inhibition thus obtained originates at the molecular level; (2) the herbicides combines reversibly with a mechanism or site within the plant; and (3) the herbicide-mechanism complex reacts irreversibly to form products which cause growth inhibition in direct proportion to the concentration of such products. Competitive inhibition of 2,4-D by 2,4,5-T was demonstrated in an application of a mixture of these compounds to soybeans. The action of TIBA as a competitive antiauxin at the growth sites is discussed as a possible explanation for the increased inhibition obtained when it was applied in mixture with 2,4-D to soybean seedlings and yeast cultures.