Effects Of Postharvest Melatonin Treatment On Storage Quality And Reactive Oxygen Species Metabolism Of Nanguo Pears

Nanguo pear belongs to Pyrus ussriensis Maxim and is one of the characteristic fruits of Liaoning Province.After harvesting,the fruit needs to be ripened to achieve the best eating quality and show a unique flavor,but the fruit is not resistant to storage and is perishable.Therefore,it is of great significance to develop a technology that can extend the storage period of the fruit and maintain the quality.Nanguo pears were used as the materials to study the effects of postharvest melatonin treatment on fruit quality,enzyme activity and gene expression of cell wall degradation and reactive oxygen species metabolism.The main results are as following:1.Melatonin treatment did not significantly affect the weight loss,flesh hardness,soluble solids content and titratable acid of Nanguo pears.Melatonin treatment significantly inhibited the ethylene release of the fruit,improved the color of the surface,suppressed the degradation of chlorophyll,and maintained the higher storage quality of the fruits.2.Melatonin treatment suppressed the production of water soluble pectin and the decomposition water insoluble pectin in Nanguo pears.The activities of polygalacturonase（PG）,pectinomethylesterase（PME）,β-glucosidase（β-Glu）and cellulose（Cx）were inhibited by melatonin treatment.Moreover,melatonin treatment also down-regulated the expression levels of PCPG1,PCPG2,PCPME,PCβ-glu 13 and PCβ-glu40 genes in the fruits.3.Melatonin treatment inhibited the activity of catalase（CAT）,enhanced NADPH oxidase（NOX）,superoxide dismutase（SOD）,peroxidase（POD）,ascorbate peroxidase（APX）,glutathione reductase（GR）,dehydroascorbate reductase（DHAR）and monodehydroascorbate reductase（MDHAR）activities in Nanguo pears.Hydrogen peroxide（H₂O₂）,ascorbic acid（As A）and reduced glutathioun（GSH）contents in the fruits were also increased by melatonin treatment.In addition,melatonin treatment also down-regulated the gene expression of Pc CAT,and up-regulated the gene expression of Pc SOD,Pc APX,Pc GR and Pc DHAR in Nanguo pears.In conclusion,melatonin treatment can maintain higher fruit quality,delay fruit softening,and improve antioxidant system,thus delaying senescence and prolonging storage period of Naguo pears.