Effect And Mechanism Of Salicylic Acid On Inhibiting Yellowing Of Fresh-Cut Chinese Water Chestnut

Chinese water chestnut(Eleocharis dulcis)is a characteristic aquatic vegetable in China,and the fresh-cut Chinese water chestnut processed from its corms is a kind of leisure food with increasing demand.However,the surface of fresh-cut Chinese water chestnut is easily yellowed during storage,which seriously affects its commodity value.Yellowing of fresh-cut Chinese water chestnut is significantly different from traditional enzymatic browning,and traditional browning inhibitors such as ascorbic acid and citric acid cannot effectively delay its yellowing.Our previous study found that exogenous Salicylic acid(SA)treatment can significantly delay the yellowing of fresh-cut Chinese water chestnut,but the molecular mechanism is still unclear.In order to further study the delay effect and its inhibition mechanism of SA treatment on yellowing of fresh-cut Chinese water chestnut,the main research contents of our studies are as follows:(1)By studying the delayed effect of different concentrations of SA treatment on yellowing of fresh-cut Chinese water chestnut during storage,it was found that SA treatment with a concentration greater than 10 m M could effectively delay the yellowing of fresh-cut water chestnut.SA treatment significantly inhibited the enzymatic activities of key enzymes PAL,4CL,C4 H and CHS in Chinese water chestnut flavonoid metabolism pathway.At the same time,the expression of these key coding genes was also significantly inhibited.(2)Metabolome technique based on UPLC-MS/MS was used to analyze the flavonoids metabolites species and content in 5 groups of fresh cut Chinese water chestnut samples: 0d,3 d control,3 d SA,6 d control and 6 d SA.The results showed that SA treatment significantly inhibited the accumulation of flavonoids in Chinese water chestnut samples,among which the accumulation of the metabolites such as kaempferol-3-O-(6"-p-coumaryl)glucoside,urushivotin,naringenin and sacherol-3’-o-glucoside were the most significant.(3)In order to explore the molecular mechanism of SA inhibiting flavonoids metabolism in fresh-cut Chinese water chestnut,this study conducted non-reference transcriptome sequencing on 3 groups of of fresh cut Chinese water chestnut samples at 0d,3 d control and 3 d SA were performed.Through analysis of transcriptome sequencing data,it was found that a large number of differentially expressed genes were concentrated in secondary metabolism and flavonoid metabolism pathway after SA treatment,and the expression of key structural genes in flavonoid metabolism pathway was significantly inhibited by SA treatment.SA treatment also had significant effects on the expression of key genes of hormone synthesis pathway.SA treatment significantly inhibited the expression of structural genes related to jasmonic acid synthesis and delayed the expression decline of genes related to ABA synthesis during storage of fresh-cut Chinese water chestnut.(4)In order to verify the correlation between the change of hormone content and yellowing of Chinese water chestnut,hormone content in Chinese water chestnut was determined.SA treatment could significantly inhibit the increase of jasmonic acid content and delay the decrease of ABA content during storage of fresh-cut Chinese water chestnut.Exogenous ABA treatment could delay the yellowing of Chinese water chestnut to some extent,but could not completely inhibit the yellowing.ABA treatment did not significantly promote the synthesis of flavonoids in fresh-cut Chinese water chestnut,and the degree of yellowing was little different from that in the control group.(5)Cw MYC2 and Cw MYC4 were selected from the differentially expressed b HLH transcription factors,and their expressions were significantly inhibited by SA treatment,suggesting that they might be involved in the regulation of flavonoids synthesis in Chinese water chestnut.Cw MYC2 and Cw MYC4 were overexpressed in tobacco leaves,and it was found that Cw MYC2 and Cw MYC4 could increase the expression of genes related to flavonoid metabolism in tobacco leaves,and lead to the synthesis and accumulation of a large number of flavonoids such as sacherol,kaempferol and naringin.In summary,exogenous SA treatment has a significant delaying effect on yellowing of fresh-cut Chinese water chestnut,and unlike typical enzymatic browning,the key to color protection of Chinese water chestnut is to inhibit the flavonoid metabolism during storage,among which SA treatment inhibited the accumulation of jasmonic acid and the expression of MYC transcription factor,which may be the main reason of inhibiting flavonoids metabolism and delaying yellowing of Chinese water chestnuts.