Promotion of plant growth and inhibition of enzymic degradation of indole-3-acetic acid by metabolites of carbofuran, a carbamate insecticide

Abstract

The carbamate insecticide carbofuran (2,2-dimethyl-2,3-dihydrobenzofuranyl-7-N-methyl carbamate) and three of its metabolites (7-hydroxy-2,2-dimethyl-2,3-dihydrobenzofuran (III), 3,7-dihydroxy-2,2-dimethyl-2,3-dihydrobenzofuran (IV), and 3-keto-7-hydroxy-2,2-dimethyl-2,3-dihydrobenzofuran (V)) stimulated growth in the pea stem segment assay in the presence, but not absence, of a low concentration of indole-3-acetic acid (IAA). The metabolites were more active than carbofuran itself. The synergistic effect on growth was specific with IAA since it was not observed in the presence of other auxins.Metabolites III, IV, and V and, to a lesser degree, carbofuran were found to be inhibitory to IAA degradation catalyzed by pea stem tissue or purified horseradish peroxidase (EC 1.11.1.7). Comparison of the relative activities of the compounds in the inhibition of IAA degradation and in the promotion of plant growth suggests a causal relationship. The implication is that carbofuran may promote plant growth through the inhibitory action of its metabolites on enzymic breakdown of IAA, thus preserving a critical level of IAA required for growth promotion.