Effects on transmembrane proton gradient and lipid biosynthesis in the mode of action of diclofop-methyl

Shimabukuro, R.H.; Hoffer, B.L.

Effects on transmembrane proton gradient and lipid biosynthesis in the mode of action of diclofop-methyl

1994

Shimabukuro, R.H. | Hoffer, B.L.

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) (Em) 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 [14C]acetate. The rate of incorporation of [14C]acetate into cellular lipids was reduced significantly by 100 micromolar 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 mM) (2,3-epoxy-4-oxo-7,10-dodecadienamide) did not depolarize Em 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.

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