In vitro hydroxylation of bentazon by microsomes from naphthalic anhydride-treated corn shoots

In vitro metabolism of the herbicide bentazon was studied in microsomal membranes isolated from 6-day-old etiolated corn shoots. Microsomes isolated from shoots of nontreated seeds did not metabolize bentazon when assayed with NADPH or peroxides. However, microsomes isolated from shoots of seeds pretreated with naphthalic anhydride formed a single bentazon metabolite when provided with NADPH. The metabolite was identified as 6-hydroxybentazon, the major phase I metabolite produced in vivo. In vitro formation of this metabolite was strongly inhibited by carbon monoxide, nitrogen, and tetcyclacis (10 microM). The results suggest that aryl hydroxylation of bentazon in corn shoots is catalyzed by a cytochrome P-450 (E.C. 1.14.14.1) and that a seed pretreatment with naphthalic anhydride is necessary for recovery of activity in vitro.