Effects Of Postharvest Melatonin Treatment On The Storage Quality And Phenylpropanoid Metabolism Of Apple Fruit(cv.Golden Delicious)

Postharvest decay and senescence are important factors that cause economic loss of apple.Melatonin has attracted much attention from botanists because of its extensive presence in the plants and its important role in regulating plants development and fruit ripening."Golden delicious" apples were used as the materials to investigate the effects of postharvest melatonin soaking storage quality and phenylpropanoid pathway during room temperature storage.The main findings are as follows:1.Postharvest melatonin treatment significantly inhibited lesion development of apple fruit inoculated with P.expansum.Postharvest melatonin treatment significantly inhibited the respiration rate and ethylene release of apple fruits,and delayed the decrease of flesh firmness and titratable acid.In addition,the contents of ascorbic acid,soluble solids and soluble sugar was significantly increased,and the increase of a and b values in the color difference was inhibited by melatonin.2.Postharvest melatonin treatment remarkably suppressed the activities of sucrose acid invertase,neutral invertase,sucrose synthase-cleavage,sorbitol dehydrogenase,sorbitol oxidase and malate dehydrogenase.Applying melatonin distinctly increased the activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase,glucose phosphate isomerase,sucrose synthase-synthesis and sucrose phosphate synthase in apples.3.Postharvest melatonin treatment significantly increased phenylalanine ammonia-lyase,peroxidase,cinnamic acid-4-hydroxylase,polyphenol oxidase,4-coumarate coenzyme a ligase and laccase activities,and improved the lignin,phenylalanine,tyrosine,tryptophan,coumaric acid,ferulic acid,caffeic acid,sinapic acid,total phenols and flavonoids contents in apples.All these results suggest that postharvest melatonin treatment delayed ripening and senescence,disease resistance of apples by regulating the enzyme activities related to glucose metabolism,respiratory metabolism and phenylpropanoid pathway to accumulate secondary metabolites.