Enantioselective Toxical Biology Effects Induced By Oxidative Stress Of Glufosinateto Model Organisms

In recent years,with the increasing application of chiral pesticides,they had become an important issue in environmental safety.As a non-selective,broad-spectrum and contact-kill herbicide,glufosinate can control weeds fast.The glufosinate can be applied to the transgenic crops,so its use is increasing year by year.In 2016,the amount of glufosinate was 12 000 tons in the world,the application amounts in Canada accounting for 40% of the total.As the glufosinate residue in the environment had increased yearly,the potential ecological safety and health risks of glufosinate had also attracted the social attention.As the studies showed that glufosinate can inhibit the synthesis of glutamine synthetase(GS),resulting in the obstruction of glutamine synthesis,nitrogen metabolism disordering and ammoniumion accumulation,and the photosynthesis of plants is prevented,so plantsdied.Previous studies on the environmental safety of glufosinate mainly focused on the effects of Rac-glufosinate on the growth,photosynthesis and secretion of algae toxins in unicellular algae.As a chiral herbicide,Rac-glufosinate consists of two enantiomers,D-glufosinate and L-glufosinate,and L-glufosinate is a high-efficient herbicide.Only a few studies had shown that there are obvious enantioselective differences in the growth and metabolite formation of wheat so far.Butthe enantioselective research on the toxicity of non-target crops and aquatic animals is lacked.This experiment mainly studied the Rac-and L-glufosinate on the growth mechanism and enantioselectivities of non-target plant maize seedlings,target plant echinochloa crusgalli and aquatic model organism zebrafish.The main results were as the following:(1)The effects of different concentrations of Rac-and L-glufosinate on the growth of maize seedlings,the antioxidant enzymes activities and the target enzyme activity in leaves were investigated.The results showed that after exposed to concentrations of 1,5,10,and 20 mg/L for 5 days,their growth morphologies were significantly affected,the plant height and weight of maize seedlings were significantly inhibited and and the leaves also were shrunk significantly.At 10 mg/L,the plant heights of maize seedlings treated by Rac-and L-glufosinate were reduced to33% and 27% of the control group,respectively,and the plant weights were reduced to 37% and 35% of the control group,respectively.The study analyzed the enantioselective of oxidative stress at 1 and 5 mg/L.Antioxidant systems,including superoxide dismutase(SOD),catalase(CAT),peroxidase(POD)and glutathione reductase(GR)activities and malondialdehyde(MDA)content were increased with the increase of the glufosinate concentration,and there were significant differences between the L-and Rac-glufosinate treatment groups.At 1 mg/L,the SOD,CAT,POD GR activities and MDA content in the L-glufosinate treatment groups were 1.36,1.16,1.51,1.65 and 1.65-folds higher than that of the Rac-glufosinate treatment groups.After treated by glufosinate,the GS activity was significantly inhibited.At 1mg/L,the GS activities after exposed to Rac-and L-glufosinate were reduced to 80%and 57% of the control group,respectively.(2)When the target plantechinochloa crusgallis were exposed to Rac-and L-glufosinate,they were seriously inhibited.The most visible signs were that the plant heights were inhibited,the growth rate was slowed down and the leaves became yellow.And the inhibition was gradually strengthened with the increasingconcentration.After treated by Rac-and L-glufosinate at 1 mg/L,the shoot heights were reduced to 79% and 69% of the control group,respectively.They were reduced to 64% and 43% of the control group at 5 mg/L,respectively.This result showed that the L-glufosinate is more pronounced than Rac-glufosinate and there were significant differences between L-and Rac-glufosinate treatment groups.(3)The median lethal concentration(LC50)of Rac-glufosinate to zebrafish embryos at 96 hpf was 21.97 mg/L,but the L-glufosinate has a low mortality rate to zebrafish embryos.The half-maximal effec concentration(EC50)of the malformation was 15.08 mg/L at 48 hpf,and the EC50 of L-glufosinate was higher than that of Rac-glufosinate.The hatching rate of zebrafish embryos treated by Rac-glufosinate at48 hpf was increased at 0.01,0.1,1.0 and 5 mg/L,but these were inhibited at the high concentrations.All zebrafish embryos at 72 hpf were hatched,whereas the hatching rate of zebrafish embryos in the L-glufosinate treatment group was similar to the control group.When the zebrafish embryos were exposed to glufosinateat 15 mg/L,the SOD and CAT activities and MDA content in the Rac-glufosinate treatment group were 1.13,1.21,and 1.53 times of that of the control group,respectively.There was no significant difference between L-glufosinate treatment and the control groups.The expression levels of Mn-SOD,Cu/Zn-SOD and CAT genes after exposed to Rac-glufosinate at 15 mg/L were 1.19,1.23 and 1.20-time higher of the control group,respectively.These genes of the L-glufosinate treatment group were not significantly different from those in the control group,indicating that Rac-glufosinate stimulated genes expression related to antioxidant enzyme in zebrafish.In conclusion,the toxicological effects of Rac-glufosinate were more pronounced than L-glufosinate for zebrafish embryos.