The Mechanism Of Difference In The Accumulation Of Antioxidant Substances In Fruits Of Hippophae Rhamnoides L.

Sea buckthorn(Hippophae rhamnoides L.)is a perennial deciduous shrub,small tree or tree,which is widely distributed in China.Sea buckthorn fruits are rich in bioactive substances and have good antioxidant capacity.Antioxidant capacity is an important index to evaluate fruit quality.At present,researches on antioxidant capacity of sea buckthorn fruits are mostly focused on the determination of antioxidant capacity of different varieties of sea buckthorn fruits.However,the reason for the difference in antioxidant capacity of sea buckthorn between different varieties in different growth periods is still unclear.In this study,two varieties of sea buckthorn(H.rhamnoides subsp.sinensis ‘Fengning'and H.rhamnoides subsp.mongolia ‘Xiangyang')fruits with large difference in antioxidant capacity were selected as materials to study its antioxidant capacity.Firstly,the relationship between the antioxidant capacity of sea buckthorn fruits and the main antioxidant properties was studied.Antioxidant capacity,total phenol content,flavonoid content,proanthocyanidins content and tannin content of sea buckthorn fruit were determined,and the correlation between antioxidant capacity and other physiological indexes was analyzed.At the same time,UPLC-MS and RNAseq technologies were used to measure and analyze the total metabolites and transcripts of sea buckthorn fruits at three different growth stages between two varieties,and combined with physiological data to search for the metabolites,metabolic pathways and key genes in the metabolic pathways that affect the significant difference in antioxidant capacity of fruits of the two varieties.The structure and function of the gene family of sea-buckthorn glycosyltransferase were analyzed,and the flavonoid glycosyltransferase in sea-buckthorn was found,and the protein prokaryotic expression of the corresponding gene was carried out.The results of physiological data of sea buckthorn fruit shows that antioxidant capacity,total phenol content,flavonoid content,procyanidins content and tannin content of Fengning fruit were significantly higher than that of Xiangyang fruit.And the content of phenolic substances including flavonoids and procyanidins in sea buckthorn fruits was positively correlated with the antioxidant capacity of sea buckthorn fruits.The results of analysing metabolism of sea buckthorn fruits shows that 23 metabolites in Fengning fruits were significantly higher than those in Xiangyang fruits during three developmental stages.In addition,13 of the 23 different metabolites belong to phenolic substances,11 of the 13 phenolic substances belong to flavonoids,and seven of the 11 flavonoid metabolites are in the form of glycosylation.WGCNA analysis was performed based on the differential expression genes of transcriptome and physiological data in sea buckthorn fruit,and four significantly correlated co-expression modules were selected.And then,GO and KEGG pathway analysis were performed in the four selected co-expression modules,results show that the gene expression related to flavonoid metabolism in Fengning fruits was significantly higher than that in Xiangyang fruits.The results suggested that the differential expression of flavonoid metabolization-related genes influenced the difference of flavonoid content in sea buckthorn fruits.The structure and function of glycosyltransferase gene in sea buckthorn fruit were analyzed,and results show that 13 glycosyltransferase genes may be involved in the synthesis of flavonoid glycosylation derivatives,and we successfully expressed protein of them in prokaryotes.In this study,it was found that the antioxidant capacity of Fengning fruits was significantly higher than that of Xiangyang,and the phenolic substances,especially flavonoids,in the fruits of sea buckthorn were the important reasons for the differences in antioxidant capacity between the two varieties.On the one hand,the difference in flavonoid content between fruits of two sea buckthorn varieties was caused by the different expression of catalytic enzyme genes related to flavonoid metabolic.On the other hand,flavonoid glycosyltransferase gene catalyzed the generation of corresponding flavonoid glycoside derivatives,thus enriching the flavonoid species in sea buckthorn fruits and affecting the accumulation of flavonoid content.In this study,the effects of phenolic substances,especially flavonoids,on the antioxidant capacity of sea buckthorn fruits were elaborated and the molecular mechanism was explored,which has important guiding significance for the molecular breeding of sea buckthorn and the selection of excellent varieties.