Mechanism Of Reactive Oxygen Species And MAPK Cascade In Senescence Of Doteur Jules Guyot Pears Regulated By Acibenzolar-S-Methyl

Senescence is the normal physiological metabolism of fruits and vegetables after harvest,and the key factor that causes quality breakdown.Studies have shown that reactive oxygen speciesis(ROS)is one of the pivotal factors that cause senscence of fruits and vegetables,and the mitogen-activated protein kinase(MAPK)cascade is involving in a series of defense reactions as a signal transduction pathway.Doteur Jules Guyot pears were used as the materials to explore the effect of postharvest acibenzolar-S-methyl(ASM)and PD98059(an inhibitor of MAPK cascade)treatments on ROS metabolism,MAPK cascade,transcription factor and pigment metabolism during storage at room temperature.The main findings are as follows:(1)ASM treatment increased H₂O₂,glutathione(GSH)and ascorbate(As A)contents,and also enhanced the activities and gene expressions of glutathione reductase(GR),ascorbate peroxidase(APX),peroxidase(POD),superoxide dismutase(SOD),NADPH oxidase(NOX),monodehydroasorbate reductase(MDHAR)and dehydroascorbate reductase(DHAR),but inhibited catalase(CAT)activity and PcCAT expression in exocarp and flesh of pears.PD98059+ASM treatment inhibited the key enzymes activities and gene expressions in ROS metabolism,but enhanced the activity of CAT and PcCAT expression in exocarp and flesh of pears.(2)ASM treatment also promoted the relative expression of PcMAPKKK1,PcMAPKK2,PcMAPKK3,PcMAPK4 and PcMAPK6 in exocarp and flesh of pears.ASM treatment also inhibited the relative expression of PcMYC2 and PcPIF4 in exocarp and flesh of pears,and suppressed the relative expression of PcHY5,PcPIF1and PcPIF3 in the exocarp,but promoted the relative expression of PcHY5,PcPIF1and PcPIF3 in the flesh.PD98059+ASM treatment suppressed the positive effects of ASM treatment and weakened the expression of selected genes related to the MAPK cascade and some transcription factors.(3)ASM treatment inhibited ethylene release and delayed the decrease of chlorophyll content in exocarp and flesh of pears and inhibited the accumulation of?-carotenoid,lycopene and lutein in exocarp of pears.ASM treatment also suppressed the relative expression of PcNYC1,PcHCAR,PcPPH,PcSGR1/2,PcPAO,PcPSY,PcLYCB,PcCRTZ2 and PcCCS1,but promoted PcLYCE relative expression in exocarp and flesh of pears.However,PD98059+ASSM treatment accelerated ethylene release,chlorophyll decomposition and carotenoid synthesis,and improved expression of genes related to chlorophyll breakdown and carotenoid synthesis in exocarp and flesh of pears.In summary,postharvest ASM treatment promoted ROS metabolism in pears and activated the MAPK cascade,thereby phosphorylated the expression of transcription factors related to the metabolism of chlorophyll and carotenoid,inhibited ethylene production,and delayed ripening and senescence of pears.