EFFECTS OF THE HERBICIDE SETHOXYDIM AND THE SAFENER DICHLORMID ON LIPID-SYNTHESIS AND ACETYL-COA CARBOXYLASE ACTIVITY OF GRAIN-SORGHUM

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 carboxylase (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-mu-M each. Sethoxydim applied alone at 50 and 100-mu-M, inhibited the incorporation of [C-14]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-mu-M. Sethoxydim applied alone inhibited the incorporation of [C-14]leucine into sorghum leaf protoplasts only at 100-mu-M. 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-mu-M 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-mu-M. 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).