Effects Of 1-MCP Treatment On The Antioxidant System And Phenolic Metabolism Of Postharvest Gynura Bicolor DC

Gynura bicolor DC（G.bicolor）,rich in polyphenols,amino acids,lipids and minerals,is a vegetable with both nutritional and medical value.Postharvest G.bicolor is prone to the problems of sensory quality and nutritional value decline,so proper storage is very important to prolong its shelf life.Previous studies have shown that 1-MCP treatment could effectively delay the quality deterioration of postharvest G.bicolor and prolong the storage period.These studies mainly focused on physiological and biochemical level about the effects of 1-MCP on postharvest G.bicolor,yet few studies at the transcription and metabolite levels.In the study,G.bicolor was treated by 10μL L^-1 1-methylcyclopropene for 6 h and stored at room temperature for 7 d.Based on full-length transcriptome sequencing,next generation sequencing and widely targeted metabolome,effects of 1-MCP treatment for 6 h on the antioxidant system and phenolic metabolic pathways of G.bicolor were examined,the conclusions are as follows:（1）The full-length transcriptome sequencing of postharvest G.bicolor was carried out to constructed reference transcriptome library.12877 de-redundant full-length transcript sequences with an average length of 2292 bp were obtained,and a total of12276sequences were annotated in data base.Next-generation sequencing results showed that 258,1157,and 344 DEGs respectively was obtained in G.bicolor treaded by 1-MCP on days 1,3,and7.The result of KEGG pathway enrichment showed that 1-MCP treatment significantly regulated phenylpropane biosynthesis.What’s more,the antioxidant system was significantly regulated by 1-MCP treatment.（2）A total of 570 metabolites were detected in G.bicolor using widely targeted metabolome technology.Flavonoids（117）and phenolic acids（78）are the most metabolites.The result of KEGG pathway enrichment showed that the 42 differential metabolites caused by 1-MCP treatment were mainly enriched in flavonoid biosynthesis,phenylpropanoid biosynthesis.Among them,8 differential metabolites including naringenin,naringenin chalcone,kaempferol,dihydrokaempferol,hesperetin,cinnamic acid,ferulic acid and chlorogenic acid,were enriched in phenolic metabolic pathways.（3）1-MCP treatment delayed the decline of the sensory quality of G.bicolor,decreased the respiration intensity and electrolyte leakage,and suppressed the accumulation of O₂^·-and H₂O₂.1-MCP maintained the contents of ascorbic acid and glutathione.Meanwhile,1-MCP stimulated the expression of genes related to antioxidant enzymes（GbSOD,GbAPX1,GbCAT,GbGR,）to varying degrees,and further strengthened the activity of SOD,APX,CAT,and GR in the different storage time.（4）1-MCP treatment increased the content of total phenolics,flavonoids and anthocyanins but decreased that of lignin,leading and the enhancement of antioxidant capacity of G.bicolor.Correlation analysis result showed that 1-MCP increased the contents of cinnamic acid,kaempferol,rutin,and chlorogenic acid by upregulating the expression of gene（GbPAL,GbCHS,GbDFR,GbANS and GbUFGT）related to flavonoid and anthocyanin biosynthesis and improving the activity of PAL and 4CL,leading the accumulation of total phenolics;but reduced the ferulic acid content by downregulating the expression of genes（GbC4H,GbCOMT,GbF5H and GbCCoAOMT）related to lignin biosynthesis.On the other hand,1-MCP inhibited the rise of PPO and POD activity to delay the degradation of phenolics.