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

The effects o f individual or combined treatment o f the cyclohexanedione herbicide sethoxy­ dim and the safener dichlormid on total lipid synthesis, protein synthesis and acetyl-CoA car­ boxylase (ACCase, EC 6.4.1.12) activity o f grain sorghum [Sorghum bicolor (L.) M oench, var. G623] were investigated. Sethoxydim and dichlormid were tested at concentrations o f 0, 5, 50, and 100 |iM each. Sethoxydim applied alone at 50 and 100 ( im , inhibited the incorporation o f [l4C]acetate into total lipids o f sorghum leaf protoplasts by more than 50%, following a 4 h incubation. Dichlormid antagonized partially the inhibitory effects o f sethoxydim on the in­ corporation o f acetate into total lipids o f sorghum protoplasts only when it was used at 100 |iM . Sethoxydim applied alone inhibited the incorporation o f [l4C]leucine into sorghum leaf protoplasts only at 100 ^m. Dichlormid was not inhibitory o f this process at any concen­ tration. The combined effects o f sethoxydim and dichlormid on this process were mainly addi­ tive indicating no interactions o f the two chemicals. Sethoxydim applied alone at 5 and 50 (iM inhibited the activity o f ACCase extracted from leaf tissues o f grain sorghum seedlings by 58 and 90%, respectively. Addition o f the safener dichlormid to the assay medium did not inhibit ACCase activity o f sorghum leaves even at the high concentration o f 50 |iM . The combined effects o f sethoxydim and dichlormid on the activity o f sorghum ACCase were similar to those observed when sethoxydim was used alone. These results indicate that the protection con­ ferred by dichlormid on grain sorghum against sethoxydim injury can not be explained on the basis o f an antagonistic interaction o f the two chemicals on target metabolic processes (lipid synthesis) or target enzymes (ACCase).