The effects of the sorghum seed safeners on sorghum mixed-function oxidase activity and chloroacetamide metabolism

Abstract

The chloroacetamide herbicides are effective in controlling many grassy weeds. The commonly used chloroacetamide herbicides are alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]. Through the use of chemical safeners, these herbicides can be used in sorghum (Sorghum bicolor (L.) Moench.). Research was conducted to determine if safeners such as flurazole [phenylmethyl 2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylate] and CGA-92194 [alpha-[(1,3-dioxolan-2-yl-methoxy)imino] benzeneacetonitrile] are potential inducers of mixed-function oxidase activity. Induced metabolism of the herbicides by mixed-function oxidases may account for sorghum's increased tolerance to the herbicides. The objectives of this research were to develop an assay to monitor mixed-function oxidase activity and to determine the capability of the mixed-function oxidases in metabolizing alachlor in the presence of the safener flurazole. The assay for mixed-function oxidase activity monitored the epoxidation of aldrin (1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,4-endo-exo-5,8 dimethanonapthalene) to dieldrin (1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octahydro-1,4-endo-exo-5,8 dimethanonapthalene). The assay was developed using house flies (Musca domestica L.). In vivo experiments were conducted with 3-day old, etiolated sorghum coleoptiles. Other experiments utilized in vitro procedures with partially purified microsomal preparations from sorghum coleoptiles. The results indicated that mixed-function oxidase activity in sorghum coleoptiles can be induced by flurazole and CGA-92194. The conversion of aldrin to dieldrin was increased after 4 h during the assay. Alachlor was metabolized more rapidly in sorghum coleoptiles which had been treated with flurazole as compared to untreated coleoptiles. Flurazole degraded very rapidly in the coleoptiles. The results of the in vitro experiments indicated that aldrin was metabolized to dieldrin by the mixed-function oxidase preparation. Even the safener flurazole was quickly degraded by the mixed-function oxidases. Alachlor was not metabolized by a mixed-function oxidase preparation. Even the treatments with flurazole did not enhance alachlor metabolism.