Effects of the Herbicide Sethoxydim and the Safener Dichlormid on Lipid Synthesis and Acetyl-CoA Carboxylase Activity of Grain Sorghum

Abstract

Abstract The effects of individual or combined treatment of the cyclohexanedione herbicide sethoxy­dim and the safener dichlormid on total lipid synthesis, protein synthesis and acetyl-CoA car­ boxylase (ACCase, EC 6.4.1.12) activity of grain sorghum [Sorghum bicolor (L.) Moench, var. G 623] were investigated. Sethoxydim and dichlormid were tested at concentrations of 0, 5, 50, and 100 μM each. Sethoxydim applied alone at 50 and 100 μm , inhibited the incorporation of [14C]acetate into total lipids of sorghum leaf protoplasts by more than 50% , following a 4 h incubation. Dichlormid antagonized partially the inhibitory effects of sethoxydim on the in­corporation of acetate into total lipids of sorghum protoplasts only when it was used at 100 μM . Sethoxydim applied alone inhibited the incorporation of [14C]leucine into sorghum leaf protoplasts only at 100 μm. Dichlormid was not inhibitory of this process at any concen­tration. The combined effects of sethoxydim and dichlormid on this process were mainly addi­tive indicating no interactions of the two chemicals. Sethoxydim applied alone at 5 and 50 μM inhibited the activity of ACCase extracted from leaf tissues of grain sorghum seedlings by 58 and 90% , respectively. Addition of the safener dichlormid to the assay medium did not inhibit ACCase activity of sorghum leaves even at the high concentration of 50 μM . The combined effects of sethoxydim and dichlormid on the activity of sorghum ACCase were similar to those observed when sethoxydim was used alone. These results indicate that the protection con­ferred by dichlormid on grain sorghum against sethoxydim injury can not be explained on the basis of an antagonistic interaction of the two chemicals on target metabolic processes (lipid synthesis) or target enzymes (ACCase).