Effects Of Acibenzolar-s-methyl On Ca²⁺-mediated Phenylpropanoid Metabolic Pathway In Doteur Jules Guyot Pears During Storage

Acibenzolar-S-methyl(ASM)is a synthetic inducer that induces postharvest disease resistance in pear fruit.Activation of phenylpropane metabolism through signal transduction is one of the mechanisms to induce host resistance.Ca²⁺and reactive oxygen species(ROS)are important signaling molecules in plants,but how they coordinate the disease resistance of pear fruits is still lack of further study.Doteur Jules Guyot pears were used as the materials to investigate the effect of acibenzolar-S-methyl(ASM)and Ca²⁺inhibitor-ethylene glycol tetraacetic acid(EGTA)treatments on the main Ca²⁺receptor protein gene expression in Ca²⁺signal transduction,reactive oxygen species(ROS)metabolism and phenylpropanoid pathway during room temperature storage.The main findings are as follows:(1)ASM treatment enhanced the expression of Ca²⁺receptor protein PcCDPK1,PcCDPK2,PcCDPK3,PcCDPK5,PcCDPK11,PcCDPK13,PcCDPK26,PcCDPK32and Pc Ca M,Pc CML27,Pc CBL1,Pc CBL9,Pc CIPK14,Pc CIPK23 genes in exocarp and flesh of pears.EGTA+ASM treatment suppressed the expression of Ca²⁺receptor protein PcCDPK1,PcCDPK2,PcCDPK3,PcCDPK5,PcCDPK11,PcCDPK13,PcCDPK26,PcCDPK32 and Pc Ca M,Pc CML27,Pc CBL1,Pc CBL9,Pc CIPK14,Pc CIPK23 genes in exocarp and flesh of pears.(2)ASM treatment enhanced the contents of total phenols,flavonoid,lignin in exocarp and flesh of pears and the contents of p-coumaric acid and caffeic acid in exocarp.ASM treatment up-regulated the selected genes expression in lignin synthesis including phenylalanine ammonia lyase(PAL),4-coumarate coenzyme A ligase(4CL),cinnamic acid 4-hydroxylase(C4H),cinnamyl alcohol dehydrogenase(CAD),p-coumaric acid 3-hydroxylase(C3H1),cinnamoyl coenzyme A reductase(CCR),caffeic acid O-methyltransferase(COMT),caffeic acid coenzyme A-O-methyltransferase(CCo AOMT),ferulic acid 5-hydroxylase(F5H)and polyphenol oxidase(PPO)in exocarp and flesh of pears.EGTA+ASM treatments decreased the contents of total phenols,flavonoid,lignin in exocarp and flesh of pears and p-coumaric acid and caffeic acid contents in exocarp.EGTA+ASM treatments down-regulated the expression of Pc PAL,Pc4CL,Pc C4H,Pc CAD,Pc C3H1,Pc CCR,Pc COMT,Pc CCo AOMT,Pc F5H and Pc PPO genes in exocarp and flesh of pears.(3)ASM treatment enhanced hydrogen peroxide(H₂O₂),ascorbic acid(As A)and glutathione(GSH)contents,NADPH oxidase(NOX),superoxide dismutase(SOD),peroxidase(POD),ascorbate peroxidase(APX),glutathione reductase(GR),monodehydroascorbate reductase(MDHAR)and dehydroascorbate reductase(DHAR)activities in exocarp and flesh of pears.Moreover,ASM treatment up-regulated the expression of Pc SOD,Pc POD,Pc APX and Pc DHAR genes in exocarp and flesh of pears.EGTA+ASM treatments decreased the accumulation of H₂O₂,As A and GSH,suppressed NOX,SOD,POD,APX,GR,MDHAR and DHAR activities in exocarp and flesh of peas.Meanwhile,EGTA+ASM treatments inhibited the expression of Pc SOD,Pc POD,Pc APX and Pc DHAR genes in exocarp and flesh of pears.In conclusion,all these results suggest that postharvest ASM treatment activates the related gene expression in Ca²⁺signal transduction to regulate ROS metabolism and phenylpropanoid metabolism,thus acceralated the accumulation of secondary metabolites and strengthened cell wall to enhance disease resitance in pears.