Mechanism Of A Novel Herbicde ¹⁴C-ZJ0273

ZJ0273, propyl 4-(2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamino)benzoate, is a novel herbicide developed for pre-and post-emergence weed control in the oilseed rape field. At an application rate of 45-60 g a.i. ha-1, ZJ0273 was found to be effectively control many monocogyledonous and dicotyledonous weeds in oilseed seed rape field with the efficacy over 80%. However, the absorption, and translocation of foliar-applied ZJ0273, the metabolism of ZJ0273 in the tolerant oilseedrape and the susceptible crickwee seedlings, the bioactivity of the main metabolites of ZJ0273, still remain poorly understood, which is of great importance in the elucidation of the mechanism and selectivity of ZJ0273. The primary objective of this study was to evaluate the absorption, translocation, metabolism of ZJ0273 in different plants, the residue in the oil rape seeds, and the bioactivity of the main metabolites. The main results were as follows:1. Absorption and translocation of ZJ0273The absorption of ZJ0273 in the crickweed, corn and rice seedlings was relatively slower, with the absorption reached 10.53%,12.47% and 2.33%, respectively, at 24 hours after treatment. Great difference in the absorption were found among the tested plants, with a higher absorption in the tolerant oilseed rape. Therefore, the different absorption was not the basis of the selectivity of ZJ0273 among the different species.Movement of the absorbed 14C in the tested plants was both aeropetal and basipetal. However, more than 90.30%,88.14%,96.29%,97.28% of the absorbed 14C remained in the treated leaf of crickweed, rice, corn and oilseed rape, respectively. At 192 h after treatment, the translocation of ZJ0273 in the tested plants followed the order crickweed> rice> corn> oilseed, in accord with the order of the suscepability of the tested plants to ZJ0273, which indicated that the different translocation between the tolerant and suscetpible plants played an important role in the selectivity of ZJ0273 among the species.2. Metabolism of ZJ0273 in the plantsEight metabolites of ZJ0273 in the oilseed rape seedlings were identified, includingM1:(propyl4-(N-(4,6-dimethoxypyrimidin-2-yl)-N-(2-hydroxybenzyl)amino)benzoate); M2:(propyl4-(N-(2-(4,6-dimethoxypyrimidin-2-yloxy)benzyl)formamido)benzoate);M3:(4-(2-(4,6-dimethoxypyrimidin-2-yloxy)benzamido)benzoic acid),M4:(propyl4-((2-(4,6-dimethoxypyrimidin-2-yloxy)phenyl)(methylol)methylamino)benzoate),M5:(4-(2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamino)benzoic acid),M6:(methyl 2-(4,6-dimethoxypyrimidin-2-yloxy)benzoate),M7:(2-(4,6-dimethoxypyrimidin-2-yloxy) benzoic acid),M8:(a conjugation product with glucose).In the crickweed, M1, M2, M3, M5, M7, M8 were identified as the metabolites of ZJ0273. The inhibition effect on the crickweed, rice, corn, and broomcorn caused by M7 was more severe than ZJ0273 and M5, which indicated a higher herbicidal activity of M7 compared to M5 and ZJ0273. Thus, it could be concluded that the metabolite M7 played the dominant role in the herbicidal activity of ZJ0273.ZJ0273 transformed to the metabolite M7 (2-(4,6-dimethoxypyrimidin-2-yloxy) benzoic acid) to a high level of 10.41% of the total extraction at 12 d after treatment. M7 was proved to have a good inhibition on the ALS, and thus caused the ceasation of the synthesis of the branched-chain amino acids, which contributed to the main mechanism of the subsequent injury posed on the susceptible plants by ZJ0273.The metabolism of ZJ0273 in the susceptible crickweed was quite different from that in the oilseed rape. More metabolites of ZJ0273 was found in the oilseed rape than the crickweed. However, a higher rate and level of ZJ0273 transformation to the herbicidal metabolite M7 was found in the crickweed than the oilseed rape, which was the basis of the selectivity of ZJ0273 between the tolerant and the susceptible plants.Conjugation of ZJ0273 and/or its metabolites with glucose, cellulose, glutathione, and among other, was found in both the tested plants, which was believed to cause the detoxification of ZJ0273. However, no significant difference was found in the percentage of the conjugation between oilseed rape and crickweed. Thus, conclusions could be drawn that the conjugation was not the basis of the selectivity.3. Residues of ZJ0273 in the oilseed rapeThe dominant component in the extractable residue of ZJ0273 in the oil rape seeds were determined to be the praent compound ZJ0273 with a concentration of 0.09 mg per kg dry weight. The residue level in oil rape seeds suggested a low dietary exposure for humans if recommended application rates were followed. Only a low level of the bound residues of ZJ0273 and/its metabolites were found in the oil seeds.4. The cause of the phytotoxicity by the soil bound residue of ZJ0273Dose-dependent and significant inhibition on rice seedlings caused by the bound residue were found at 14 d after treatment, while no significant inhibition occurred to corn seedlings in the same treatment. The phytotoxicity is mainly caused by the release of the biologically active metabolite M7 from the soil bound residue during the rice cultivation. This knowledge is valuable for designing crop rotation practices so that crop injury and yield losses due to carry-over herbicide phytotoxicity may be avoided.