Chloroacetamide mode of action, II: Inhibition of very long chain fatty acid synthesis in higher plants

In short-term-experiments [C-14]-labelled malonic acid, stearic acid and ac etate have been incorporated into leaf fatty acids of seedlings of Cucumis sativus, Hordeum vulgare and Zea mays. The pattern of labelled fatty acids changed markedly by treatment with the chloroacetamide herbicides metazachl or, metolachlor or butachlor. During a 2-h incubation time, 1 mu M chloroac etamide specifically inhibited up to 100% the formation of the saturated ve ry long chain fatty acids (VLCFAs) with a carbon number of 20, 22 and 24. I n cucumber and barley a 50% inhibition of VLCFA formation is achieved with 10 to 100 nM metazachlor representing the most sensitive effect of inhibito rs on fatty acid elongation reported as yet. Sensitivity of fatty acid elon gation depends on the amide structure present in the compound and on its st ereochemistry. Inhibition of oleic acid incorporation correlates with growt h inhibition by chloroacetamides of the intact cell (comp. Pestic. Sci. 52, 381-387, 1998). The present study extends this correlation to inhibition o f VLCFA synthesis in higher plants. Obviously the primary mode of action of chloroacetamides and related herbicidal substances is involved in the enzy mic four-step fatty acid elongation system.