Toxic Effects And Mechanisms Of Fluxapyroxad To Zebrafish(Danio Rerio) Embryos

Fluxapyroxad is a broad-spectrum and high-efficiency succinate dehydrogenase inhibitor(SDHI)fungicide,which is widely used in the control of various agricultural and forestry crop diseases.As the most used SDHI fungicide at present,fluxapyroxad can enter the aquatic environment easily and poses a threat to aquatic organisms.However,the potential threat and toxicological mechanisms of fluxapyroxad in aquatic organisms remain poorly understood.In this study,zebrafish(Danio rerio)embryos were used as test organisms to explore the toxic effects and mechanisms of fluxapyroxad on zebrafish embryos,so as to provide reference for the safe and rational use of fluxapyroxad.1.In the acute toxicity test,the 96 h-LC₅₀of fluxapyroxad to zebrafish embryos,larvae and adults were 1.388,0.699,and 0.913 mg/L.In addition,fluxapyroxad had negative impacts on the development of zebrafish embryos,including slow heartbeat,hatching inhibition,abnormal spontaneous movement,body length regression,and morphological deformities.2.In the sublethal toxicity test,the 1/2(0.694 mg/L),1/4(0.347 mg/L)and 1/8(0.174 mg/L)of embryos 96 h-LC₅₀were set as exposure concentrations to investigate the the toxic mechanisms of fluxapyroxad.Succinate dehydrogenase activity was significantly increased in all treatment groups,and the expression of sdh was significantly up-regulated in 0.694 mg/L fluxapyroxad;The activities of the electron transport chain complex II and Na⁺K⁺-ATPase were markedly inhibited in0.347 and 0.694 mg/L fluxapyroxad groups compared to that of the control group,the expression of the genes related to mt DNA replication and transcription(mt-nd,polg,polrmt,tk2,tfam and twinkle)and the expression of the genes related to nuclear-encoded subunits of the mitochondrial respiratory complexes(atp5?,cox5ab,sdha,ndufs4 and uqcrc2)were down-regulated in 0.694mg/L fluxapyroxad.Exposure to 0.347 and 0.694 mg/L fluxapyroxad resulted in significant increases in MDA production,and GPx activity was reduced;The expression of four antioxidant genes(cat,sod(Cu/Zn),gpx,and sod(Mn))were decreased significantly at the concentration of0.694 mg/L.Acridine orange staining test showed that fluxapyroxad exposure could induce zebrafish embryos cell apoptosis,and the degree of apoptosis increased with the increase of exposure concentration;The activity of caspase3 and the relative expression of its coding gene were significantly increased in the 0.694 mg/L group.The expression of the genes related to notochord development and bone formation(bmp4 and lox)were inhibited after 0.694 mg/L fluxapyroxad exposure.In conclusion,fluxapyroxad may cause zebrafish embryo abnormal development and even death by inducing oxidative stress,mitochondrial damage and apoptosis.