Effect Of Enantioselective Phytotoxicity Of Herbicide Imazethapyr On Physiology, Biochemistry And Gene Transcription In Rice

Chirality is a common phenomenon in life sciences. Chiral compounds account for more than 40% of currently used pesticides in China. Research increasingly suggests that chiral compounds usually behave enantio- selectively in phyto-biochemical processes. In this study, we selected Japonica rice variety Xiushui 63 seedling to evaluate enantioselectivity of imazethapyr (IM). Significant differences in rice seedling morphology, physiology, biochemistry, cytology and gene transcription were observed between the two IM enantiomers. In the seedling morphological assay, IM enantiomers inhibited elongation of primary root and shoot, reduced the number of adventitious roots. The maximal root relative inhibition rate reached 67.05%, 80.35%, after exposure to 0.5 mg/L S-(+)-IM and R-(-)-IM, respectively, and the maximal shoot relative inhibition rate reached 26.89%, 77.71%, respectively. The minimum of the number of adventitious roots was observed at 0.5 mg/L R-(-)-IM treatment and only 0.6 roots, lower than 6.6 (treated by S-(-)-IM) roots at the control. The activity of ALS was reduced to 87. 1% and 97.9% of control, at the concentration of 1.0 mg/L S-(+)-IM and R-(-)-IM, respectively. The activities of SOD, POD and CAT and the content of MDA increased at 0.5 mg/L of R-(-)-IM treatment, and were 1.78, 3.25, 1.36, 2.16 time over the S-(+)-IM, respectively. The content percentage of three branched-chain amino acids were 86.5%、90.2% and 93.4% at 0.5 mg/L of R-(-)-IM treatment over S-(+)-IM, respectively. Real-time PCR showed that R-(-)-IM reduced the transcript abundance of ALS, psaA, psaB, psbB, rbcL in shoot tissue, and reduced the transcript abundance of PC in seed. R-(-)-IM increased the transcript abundance ofβ-amy in shoot. Gene chip expression analysis showed that R-(-) enantiomer reduced the transcript abundance of BCAA and PK in the root tissues, and reduced the transcript abundance of FNR, FR, FBPase and SBPase in shoot tissue, increased the transcript abundance of PEPCK, APX and Fructose phosphate aldolase enzyme gene in rice shoot tissue.Results from this study imply that IM enantiomers have enantioselective phytotoxicity in aspects of inhibiting the growth of rice seedlings, oxidative damage, as well as photosynthesis, carbohydrate metabolism, amino acid metabolism and antioxidant gene expression, and R-(-) enantiomer was more toxic than S-(+) enantiomer. So, the behavior of the active enantiomer, instead of the racemate, may be more relevance to the herbicide effects and ecological safety of IM.