Abstract:The mechanism of the novel herbicide ZJ0273 is studied with the conventional bioassay and biochemical methods. The results indicated that the addition of 5 mg/L of 3 branched-amino acids to sorghum seedling cultures incubated in the presence of ZJ0273 completely alleviated herbicide-induced stem growth inhibition. But each of Val, Ile and Leu single was only partly effective in reversing ZJ0273-induced growth inhibition at the same concentrations. The IC50 values of ZJ0273 and bispyribac-sodium were respectively over 100 mg/L and in the ranges of 10-5-10-4mg/L in vitro, so ZJ0273 showed little inhibition effect on acetolactate synthase (ALS). ALS was greatly inhibited by ZJ0273 in vivo,and the activity of ALS was lowered when the treat time increasing. It is concluded that ZJ0273 inhibited biosynthesis of the essential branch amino acids and acted as an ALS inhibitor. However, the mode of action of ZJ0273 differs from the other typically commercial ALS inhibitors, such as sulfonylurea and pyrimidine salicylic acid herbicides. Its mechanism is similar to a pre-herbicide, and activated by the metabolic processes in the plants.