Effects of Safeners on the Oxidation of Multiple Substrates by Grain Sorghum Microsomes

Abstract

Microsomes isolated from excised shoots of 3-day-old, dark-grown, grain sorghum [ Sorghum bicolor (L.) Moench. Funk G522DR, and DK 41Y] seedlings metabolized cinnamic acid, lauric acid, metolachlor, bentazon, and diazinon. but did not metabolize triasulfuron or primisulfuron. Pretreatment of G522DR seed with safeners (naphthalic anhydride, dichlormid, flurazole, BAS 145138, oxabetrinil, fluxofenim, and benoxacor) resulted in enhanced metabolism of lauric acid, bentazon, and diazinon. However, metabolism of cinnamic acid was not affected and that of metolachlor was depressed by safener treatments. Microsomes isolated from DK 41Y seedlings had higher endogenous levels of oxidative activity for lauric acid and bentazon than microsomes isolated from G522DR seedlings. Metabolism required NADPH and was affected by CO and other cytochrome P450 monooxygenase inhibitors (tetcyclacis, piperonyl butoxide, 1-aminobenzotriazole, SKF-525A, and tridiphane). The inhibitors differentially affected metabolism of the substrates. Only tetcyclacis strongly inhibited the metabolism of all substrates except cinnamic acid. Microsomal oxidations from both unsafened and safener-treated tissue responded similarly to the inhibitors. The differential inhibitory responses suggest that each substrate was probably metabolized by a different monooxygenase isoform.