Inhibition of the Acetyl-CoA Carboxylase of Barley Chloroplasts by Cycloxydim and Sethoxydim

The effect of the three cyclohexane-1,3-dione derivatives cycloxydim, sethoxydim and clethodim on the incorpora­ tion of l4C-labelled acetate, malonate, acetyl-CoA or malonyl-CoA into fatty acids was studied in an enzyme preparation isolated from barley chloroplasts (H ordeum vulgare L. var. “A lexis”). The herbicides cycloxydim, clethodim and sethoxydim block the de novo fatty acid biosynthesis from [2-l4C]acetate and [ l 14C]acetyl-CoA, whereas that of [2-14C]malonate and [2-l4C]malonyl-CoA is not affected. The data indicate that the mode of action of the cyclohexane-1,3-dione derivatives in the sensitive bar­ ley plant consists in the inhibition of de novo fatty acid biosynthesis by blocking the acetyl-CoA carboxylase (EC 6.4.1.2.).