Effects on Transmembrane Proton Gradient and Lipid Biosynthesis in the Mode of Action of Diclofop-Methyl

Abstract The sensitive sites in the mechanism of action of diclofop-methyl (DM) (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate) are the plasma membrane and acetyl-CoA carboxylase (ACCase), a key enzyme in fatty acid biosynthesis. The hydrolysis of DM to diclofop yields the active molecule that increases the permeability of the plasma membrane to protons (depolarizes the membrane potential) ( E m ) and reduces cellular lipid biosynthesis in vivo . Coleoptiles of susceptible oat ( Avena sativa ) were used to investigate the effects of both mechanisms that function simultaneously in vivo . The action of diclofop on the membrane site was more effective than that of DM to reduce significantly the uptake of [ 14 C]acetate. The rate of incorporation of [ 14 C]acetate into cellular lipids was reduced significantly by 100 μ M diclofop but not by DM, although higher cytoplasmic concentrations of diclofop are present in coleoptiles treated with DM than in those treated with diclofop. The antibiotic cerulenin (0.45 m M ) (2,3-epoxy-4-oxo-7,10-dodecadienamide) did not depolarize E m in oat coleoptiles and slightly antagonized auxin-induced growth, but lipid biosynthesis was reduced significantly. The inhibition of auxin-induced growth in susceptible oat coleoptiles was unrelated to the inhibition of lipid biosynthesis. Diclofop induced lipid profile changes within 1 hr of treatment. Inhibition of coleoptile growth, reduction in cellular lipid biosynthesis, and lipid profile changes are probably due to factors other than the inhibition of ACCase in vivo .