Effects Of Exogenous Spermidine On DNA Methylation And Stress Resistance Enzymes Of Postharvest Apricot Fruits

"Saimaiti" apricot is a species with local characteristics in Xinjiang.It has become one of the featured forestry industries in some parts of southern Xinjiang and has been listed as a key promotion for high-quality varieties,but this variety has rapidly aged and softened at normal temperature after picking.Rot and short shelf life limited its commercialization.Therefore,it is significant to increase the added value by exploring the changes of various enzyme activities,mechanism of the activities of “Saimaiti” apricot.Spermidine(SPD)belongs to polyamines that is a low molecular aliphatic nitrogen base with strong biological activity.It is widely found in various plants that regulate cell growth and delay aging.D-Arginine(D-Arg)is a polyamine inhibitor.DNA methylation mainly regulates the expression of related genes in order to regulate the physiological and biochemical metabolism during its growth and development.The results of previous studies of this subject confirm that exogenous SPD can effectively delay ripening and aging of apricot.In order to further explore the mechanism of exogenous SPD on delaying the senescence of apricot,In this study,the Xinjiang "Saimaiti" apricot Green Maturity Phase was used as raw material that was treated with 0.1mmol/L SPD and D-Arg solution,and studied the effect of anti-oxidation enzyme activity,methionine metabolism,and methylation level.The main findings are as follows:(1)Exogenous SPD treatment increased the activities of POD,SOD and PAL enzymes of the green-maturing period “Saimaiti” apricot;Using transcriptional analysis,it was found that SPD treatment can increase the antioxidant enzyme gene expression of CAT,GR and APX and disease resistant enzyme gene expression of PPO,CHI.(2)The SPD treatment group was significantly different from the CK and D-Arg treatment groups at normal or low temperature(P<0.05),and obviously affected the methionine metabolism cycle.SPD treatment of SAM/SAH had the highest value at room temperature;SPD treatment at the low temperature at the 15th day of SAM/SAH was much greater than the other two groups.Exogenous SPD treatment could increase the methylation index and decrease the expression of Homocysteine gene,regulates the expression level of DRM and MET genes to maintain the high level of DNA methylation of “Saimaiti” apricot;D-Arg treatment reduces the gene expression levels of DRM and MET,causing low levels of DNA methylation.(3)Compared with CK,exogenous SPD treatment showed that the differentially expressed genes showed more metabolic pathways,but their improved apricot fruit quality might be related to phytohormonal signal transduction,ascorbic acid and aldarate metabolism,cysteine and methionine metabolism,amino acid biosynthesis,plant pathogen interactions and other pathways,which delay its aging.