Study On The Regulation Of Phenolic Compounds Of Grape In Response To Exogenous Melatonin

Plant melatonin(MLT)is a pleiotropic molecule with many diverse effects.It not only acts as an antioxidant,but also involves in multiple cellular and physiological process in plant.Recentily,exogenous MLT application has gained increasing attention as a new post-harvest processing method.In present study,post-harvest grape(Vitis vinifera cv.Kyoho)was soaked by200 ?M and 400 ?M exogenous MLT for 25 min,and then stored at 4 ° C for 25 days.During the storage time,the physical and chemical qualities and antioxidant properties of grapes was measured,and proteomics was applied to analyze the changes in protein levels.What's more,the levels of phenols and endogenous MLT metabolites was determined and RT-q PCR was performed to explore the effect of phenolics in response to exogenous MLT treatment and to elucidate the possible mechanisms involved.The results are as follows:The grape abscission rate was significantly reduced by 35.89% and 36.89%,respectively,and the grape rotten rate was significantly reduced by 58.37% and 59.07%,respectively,in response to exogenous MLT treatment at 200 ?M and 400 ?M(p <0.05);the increase of soluble solids content was promoted and a higher total acid level was maintained;meanwhile,the accumulation of free amino acids was promoted;total phenols was increased by 14.34% and18.51%,total flavonoids was upregulaged by 28.04% and 36.45%,and total anthocyanins content was raised by 38.11% and 30.06%,respectively,in responsed to 200 ?M and 400 ?M MLT treatment;antioxidant capacity was improved by exogenous MLT.TMT proteomics analysis found that MLT up-regulated the expression of 4 key enzymes in aromatic amino acid synthesis and 7 enzymes in phenolic substance synthesis.Furthermore,the expression of polyamine synthesis,energy metabolism,and antioxidant system related proteins was promoted,while the expression of fatty chain extension-related enzymes in fatty acid metabolism was inhibited.In addition,the expression of key genes for MLT synthesis was up-regulated by exogenous melatonin treatment and the levels of MLT and its synthetic intermediates was increased.The result of RT-q PCR aslo showed that the expression of Vv PAL was upregulated by83.82%,and Vv CHI,Vv F3H1,Vv F3H2,Vv F3'H,Vv LAR,Vv ANR,and Vv OMT genes in grape flavones biosynthesis pathway was significantly up-regulated exogenous melatonin treatment(p<0.05).And the contents of phenolics such as caffeic tartaric acid,proanthocyanidin polymers,and peonidin,petunidin,malvidin anthocyanins were increased in response to exogenous MLT treatment.Results from present study demonstrated that the accumulation of aromatic amino acids was promoted by exogenous MLT treatment to provide sufficient precursor materials for phenolic biosynthesis.Furthermore,the expression of key genes for phenolic biosynthesis was up-regulated,and the expression of key enzymes was increased by exogenous MLT treatment,and the accumulation of phenolics during grape storage was significantly promoted(p <0.05).This research provided a deep insight into the effect of MLT on grape phenolics and shed light on the application of exogenous MLT on postharvest preservation.