Molecular And Biochemical Mechanisms Associated With Reactive Oxygen Species And Defance Enzymes Of Harvested Muskmelon Fruit Treated With ASM Treatment

Acibenzolar-S-methyl(ASM), a synthetic chemical elicitor of salicylic acid, can induce disease resistance in a variety of fruits and vegetables. Muskmelon(Cucumis melo L. cv. Yujinxiang) fruits were used as the materials and applied molecular biology, biochemistry, cell biology technology to study the effect and relationship of 0.1 g/L ASM dipping treatment on enzyme activity, gene expression of reactive oxygen species(ROS) metabolism and defance enzymes and related metabolites from the molecular and biochemical levels respectively. The results showed as following:1. ASM significantly enhanced the expression and activity of superoxide dismutase, ascorbate peroxidase, glutathione reductase, but inhibited the expression and activity of catalase. The same trend was observed on expression and activity of these enzymes. ASM also enhanced the accumulation of hydrogen peroxide(H2O2) at early stage and the treatment fruits were significantly higher than control after 1day of treatment.2. ASM treatment enhanced the expression and activity of phenylalanine ammonia lyase, cinnamic acid dehydrogenase, peroxidase and caffeoyl-Co A-O-methyltransferase. A positive correlation trend was observed on expression and activity of these enzymes. The significantly accumulation of total phenolics, flavonoids and lignin were observed in ASM-treated fruit. The contents of total phenolics, flavonoids and lignin in treatment were significantly higher than control after 6 daysof treatment.3. Observation of transmission electron microscopy showed that H2O2 was localized abundantly in the cell wall of ASM-treated fruit tissues after 0.5d of treatment, while the control had a less accumulation. POD was localized abundantly in cell wall after 4d of treatment, while the control had a less accumulation.In conclusion, postharvest ASM treatment increased the content of H2O2 at early stage by regulation the gene expression and enzymes activities in reactive oxygen species metabolism. H2O2 was as a signal molecule to activate further to enhance the expression and activity of defance enzymes, to improve the accumulation resistant substances in the melon fruits, to strengthen the cell wall structure, and enhance the resistance of fruits.