| Chirality is a common phenomenon in life sciences. Chiral compound account for more than35%of currently used pesticides in China. Research increasingly suggests that chiral compounds usually behave enantio-selectively in phyto-biochemical processes. Diclofop methyl (DM) is a chiral herbicide that is widely used as a racemic mixture. In this experiment, we selected Japonica rice variety Xiushui63seedling as a target plant and analyzed enantioselective biochemical, physiological and transcriptional effects of DM enantiomers on rice seedlings. In the seedling morphological assay, DM enantiomers inhibited elongation of primary root, reduced the number of adventitious roots. The maximal root relative inhibition rate reached26.81%and53.33%, after exposure to100μg/L R-and S-DM respectively. The minimum of the number of adventitious roots was observed at100μg/L R-DM treatment and only2.5roots, lower than4.2treated by S-DM. DM also exerts an enantioselective effect on the transcription of antioxidant genes. The activities of ascorbic acid peroxidase (APX) and peroxidase (POD) increased at100μg/L of R-DM treatment for2and3weeks, and were1.91,1.26and1.12,1.48time over the S-DM, respectively. R-DM increased ROS level in rice after NBT and DAB staining than S-DM, and the content of MDA increased more significantly in R-DM treatment than that in S-DM treatment. These results showed that DM induces oxidative stress and then stimulates the antioxidant system to maintain the balance between ROS and scavenging factors. However, the concomitant increase in MDA content suggests that the antioxidant enzymes induced by DM may be insufficient to completely eliminate the ROS. DM can inhibit fatty acid synthesis and revealed that it acts in an enantioselective manner.R-DM treatment reduced the amount of total fatty acids to approximately51.5%of the control, which is lower than S-DM treatment90%of the control. DM also exhibited an enantioselective effect on chlorophyll fluorescence. After100μg/L DM treated for2and3weeks, the fluorescence parameters of photosynthesis Fv/Fm, qP, ETR(II), ΦPSⅡ,(Fo, Fo’) and Y(I) were decreased, and R-DM treantment was significantly lower than that observed after S-DM exposure. These results demonstrated that R-DM treatment strongly inhibited photosynthesis, reduced carbon assimilation and photochemical energy production. Real-time PCR showed that the transcript levels of antioxidant genes APX, CAT, SOD and GPX in rice were up-regulated by R-DM. But no antioxidant gene was affected by S-DM treatment after two or three weeks of exposure. Microarray results showed that many metabolic pathways, including starch and sucrose metabolism, oxidative phosphorylation, and amino acid biosynthesis and metabolism, were affected by DM in an enantioselective manner. These results suggest that R-DM is more toxic to plant growth than S-DM. Therefore, it is feasible that single R-DM is used to control weed instead of DM racemate to eliminate herbicides ecological toxicology. |
