Analysis Of Different Phenotype And Physiological Data Between Sunburning Peel Of Satsuma Mandarin And Ponkan Tangerine

Sunburn seriously affected fruit appearance and quality.However,the mechanism of sunburn in citrus is still unclear.In this study,we compared the physiological indexes related to the difference of sunburn between Satsuma mandarin and ponkan.In order to preliminarily explore the mechanism of difference caused by sunburn of two citrus.Comprehensive comparative analysis was conducted from the perspectives of peel injury degree,cell morphology observation,antioxidant content and gene expression level.The following conclusions were obtained:1.Ponkan peel showed enhanced sunburn tolerance compared to Satsuma mandarinThe type of sunburn suffered by the subjects was browning sunburn,and both of them showed that the fruit changed color earlier after sunburn.The degree of color change of Ponkan peel was lighter than that of Satsuma mandarin peel,and brown spots appeared in the severely burned fruits.The microstructure showed that the arrangement density of satsuma mandarin pericarp cells was seriously affected,accompanied by pericarp collapse and lignin accumulation.The pericarp of Ponkan did not cause cell death,only a few cells in the epidermis showed the trend of lignification,and the cell arrangement density was not affected.2.Ponkan showed stronger scavenging ability of reactive oxygen speciesThe difference in the accumulation of reactive oxygen species is the reason for the difference in sunburn injury between Satsuma mandarin and Ponkan peel.The content of antioxidants in the pericarp of Ponkan was significantly higher than that of Satsuma mandarin,and there was little relationship between the scavenging ability of reactive oxygen species and enzyme activity,only peroxidase was significantly up-regulated after sunburn.It was found that the content of flavonoids was one of the important reasons affecting the antioxidant capacity of both.The contents of flavonoids in Ponkan were significantly higher than that in Satsuma after sunburn.3.The metabolic pathway of polymethoxy flavonoids and its regulatory genes in Ponkan pericarp are more responsive to sunburnThe metabolites of polymethoxy flavonoid pathway represented by chuanpidin were significantly enriched in Ponkan after sunburn,the content and enrichment increase were significantly higher than those in Satsuma mandarin.The metabolites of flavonoid pathway upstream of polymethoxy flavonoids were also up-regulated by sunburn.It was found that Cr CHS2,an important rate-limiting enzyme gene in flavonoid metabolism of satsuma mandarin,was significantly up-regulated after sunburn.Cr OMT2 was the key gene in the polymethoxyflavone pathway,more significantly induced in the pericarp of Ponkan,from which it was inferred that Cr OMT2 responded specifically to sunburn.The above results showed that citrus sunburn mainly caused the decrease of fruit appearance quality and the damage of epidermal cells.The main reason for the difference of sunburn between Satsuma Satsuma and Ponkan is that there are more antioxidants in Ponkan,and the genes in flavonoid pathway were significantly up-regulated compared to Satsuma after sunburn,which can more effectively reduce the accumulation of reactive oxygen species and thus reduce the damage caused by sunburn.