Metolachlor (2-chloro- N-[2-ethyl-6-methylphenyl]- N-[2-methoxy-l-methylethyl] acetamide) and the metolachlor safener CGA 43089 [α-(cyanomethoximino)-benzacetonitrile] in sorghum seedlings: Correlations between morphological effects and ethylene formation

Abstract

Treatment of germinating sorghum [ Sorghum bicolor (L.) Moench] seeds with the grass herbicide, metolachlor (2-chloro- N-[2-ethyl-6-methylphenyl]- N-[2-methoxy-1-methylethyl] acetamide), causes growth retardation, promoted by thickening of the first leaf and thus inhibition of unfolding of secondary leaves, and increased ethylene production. Sorghum seeds pretreated with the safener CGA 43089 [α-(cyanomethoximino)-benzacetonitrile] exhibit neither morphological deformations nor ethylene production upon metolachlor treatment. Aminoethoxyvinylglycine [ l-2-amino-4-(2-aminoethoxy)-trans-3-butenoic acid], a specific inhibitor of ethylene formation in higher plants, decreases ethylene formation by metolachlor-treated sorghum seedlings; the observed deformations, however, remain unchanged. Sorghum control seedlings which grow against a covering plate build up ethylene concentrations as after herbicide treatment, but without induction of the morphological symptoms. These observations suggest that the plant hormone ethylene is a symptom and not the inducer of the morphological effects visible after metolachlor treatment of sorghum seedlings.