Enantioselective Phytotoxicity Of The Herbicide Imazethapyr On Arabidopsis Thaliana

Chirality is a common phenomenon in life sciences. Chiral compound account for more than40%of currently used pesticides. Research increasingly suggests that chiral compounds usually behave enantioselectiivity in phyto-biochemical processes. Therefore, the pesticides activity or toxicological effects obtained by achiral analysis did not stand for their real effects. In this study, we selected Arabidopsis thaliana as model plant to evaluate enantioselective effect of imazethapyr (IM) on Arabidopsis thaliana seedling morphology, physiology, subcellular structure and gene transcription. The results showed that the fresh weight relative inhibition rate of A. thaliana seedling reached73.7%,16.7%and41.2%, after exposure to2.5μg/L R-(-)-IM, S-(+)-IM and racemate, respectively; and the root relative inhibition rate reached69.5%,27.3%and31.1%, respectively. The activity of ALS was reduced to45.2%and86.5%of control after0.5mg/L S-(+)-IM and R-(-)-1M exposure, respectively. The content of three branched-chain amino acids, Leu, Val and Ile, were87.7%,87.5%and89.5%of the control at2.5μg/L of R-(-)-IM treatment, respectively. Utilizing transmission electron microscopy, we observed that R-(-)-IM treatment reduced cell size and chloroplasts number, increased the number and the size of starch granules, and damaged the structure of grana lamella. R-(-)-IM also accumulated ROS content, but drastically reduced antioxidant genes transcription and their activities, such as SOD and CAT, which may led to subcellular destruction.R-(-)-IM also resulted in the accumulation of glucose, maltose and sucrose in the plant and disturbed carbohydrates utilization. The study suggests that R-(-)-1M more strongly retarded plant growth than S-(+)-IM not only by acting on ALS, but also by causing an imbalance between the antioxidant system and the disturbance of carbohydrate metabolism with enantioselective manner.