Study On Resistant Differences Of Three Nitrogen-Fixation Cyanobacteria To New Sulfonylurea And Their Mechanisms

Sulfonylurea has been widely used in agricultural production since its invention with the characteristic of exceptional low application rates and excellent toxicological and environmental properties. Compare with its widely use, studies on inhibitory mechanism of sulfonylurea to ALS (Acetolactate-synthase) are still needed to be improved, and continually appearances of resistant weeds to this kind of herbicide makes it very necessary to make a clear understanding of the mechanism of inhibition. In this study, differences among tolerant capabilities of three species of nitrogen-fixation cyanobacteria (Anabaena azollae, Anabaena flos-aquae, Anabaena azotic) to two new sulfonylurea (Monosulfuron and Monosulfuron ester) were studied, which could be used to further explain the resistant mechanism to sulfonylurea herbicides and how these herbicides take effect.Different species of cyanobacteria showed different sensitivities to the monosulfuron and monosulfuron ester. While two herbicides had no significant effects on the growth of three cyanobacteria at low concentrations (0.01⁰.001mg/L), they made damage to cells and affect cyanobacteria's growth at high concentrations (10¹00mg/L). EC₅₀ values of three cyanobacteria were showed below: Anabaena azollae, 3.172 mg/L; Anabaena azotic, 3.654 mg/L and Anabaena flos-aquae, 3.377mg/LNitrogenase activities of three species also showed different tolerant capabilities to the two herbicides under 10% (vol. %) of acetylene. And of three cyanobacteria, nitrogenase of Anabaena flos-aquae was most easily to be affected by the two herbicides. Two herbicides had no significant effects on the nitrogenase activities of three cyanobacteria at low concentrations (0.01⁰.001mg/L), while concentration of herbicides is higher than 0.1mg/mL, nitrogenase activities of all three cyanobacteria were inhibited.Tolerant capabilities of ALS under in vitro and in vivo conditions all showed significant differences among three cyanobacteria. To monosulfuron, tolerance differences were: Anabaena azotic EC₅₀=101.3 mg/L> Anabaena azollae EC₅₀= 65.2 mg/L> Anabaena flos-aquae EC₅₀=3.322 mg/L. To monosulfuron ester, tolerance differences were: Anabaena azollae EC₅₀=613.8 mg/L> Anabaena azotic EC₅₀=106.8 mg/L> Anabaena flos-aquae EC₅₀=3.70 mg/L. ALS of Anabaena flos-aquae was most easily to be affected by the two herbicides.Comparisons of partial sequences of deduced amino acid from ALS gene among three cyanobacteria further explained the tolerant differences. Partial sequence of deduced amino acid of Anabaena flos-aquae showed many different sites compared with those of other tow cyanobacteria, which resulted in the different tolerant capability to two herbicides.