Metabolomics Analysis Of Oleocellosis In Navel Orange (Citrus Sinensis Osbeck) Fruit

Oleocellosis is a serious physiological disorder in mature and harvested citrus fruit;this disorder decreases the external quality and consequently the market value of the fruit.Oleocellosis brings huge losses to citrus industry around the world.Currently,the exact causes and physiology mechanisms related to oleocellosis are still not clear.There are few effective measures decreasing the happening of oleocellosis,which seriously restricts the development of.citrus industry.So we need to adopt new ideas for oleocellosis research.Recently,the vigorous development of metabonomics provides new technology for us to research the oleocellosis.’Fenjie 72-1’ navel orange fruits were used for the experiments shortly after harvest.Metabolomic analysis can be used to determine the pathogenesis of oleocellosis.We compared the change of the metabolite in flavedo of fruit at different degree of disease.In addition,in combination with molecular biology and physiology methods,the metabolomic analysis can be used to examine the effect of oleocellosis on fruit completely and objectively,which provides entire information about mechanisms.The main conclusions of this paper were as followed:1.The content of organic acid decreased in the course of oleocellosis,especially,butanedioic acid,malic acid and a-ketoglutaric acid which involved TCA recycle decreased more significantly along with the degree of oleocellosis.The content of glucose and glucopyranose decreased in the damaged area,however,two kinds of disaccharide:turanose and sucrose increasd gradually along with the degree of oleocellosis.The happening of oleocellosis also can affect the content of proline,aspartic acid,glutamine and asparagines in the damaged area,but this change showed volatility with the degree of disease.2.In damaged flavedo,most of the tested secondary metabolites increased significantly along with the degree of oleocellosis.The increasing of the content of phenylalanine and tryptophan in the damaged area is well worthy of attention,because this two amino acid is the key of connecting the primary metabolism and secondary metabolism.Moreover,the content of protocatechuic acid-hexoside and hydroxybenzoic acid-hexoside which relate salicylic acid metabolism also increased gradually along with the degree of oleocellosis.But the content of quercetin-3-o-rhamnoside,rutin,kaempferol-3-o-rutinoside and kaempferol-c-hexoside decreased significantly in the health area of the oleocellosis fruit,and increased to the normal level along with the development of oleocellosis.According to the pathway analysis,we investigated four genes about salicylic acid metabolism,the expression of AGD2,ALD1 and FAD7 in moderate degree of oleocellosis area were higher than normal area,but the expression of this three genes were significantly lower than the normal area.AGD1 had the lower expression only in the mild degree and the severe degree area.3.The total Zn,P,Ca2+ in damaged area were significantly higher than the normal fruit,moreover,the content of P and Ca2+ increased gradually along with the degree of oleocellosis.The content of total N was higher than normal fruit only in moderate degree and severe degree.Total K from the health area of the oleocellosis fruit and the damaged area was lower than the normal fruit.4.The activity of peroxidase(POD)was induced up-regulating in damaged area.On the other hand,H2O2 content in oleocellosis fruit was higher than that of the normal fruit.Inoculation experiments demonstrated that oleocellosis fruit have lower disease incidences and samller lesion diameter than the control 10 d after injecting.