The Evaluation And Analysis Of Citrulline Content In Watermelon Germplasm Resources And Study Of Key Genes In Citrulline Biosynthesis

Citrulline has important health care function on human body,watermelon is considered to be a natural source for citrulline because of the large amount of citrulline in the flesh and rind.However,little is known about citrulline synthesis pathway.In this study,the citrulline contents of 195 watermelon germplasm resources was determined and analyzed,two varieties with large difference in citrulline content and less affected by environment will be selected for further research.Parallel changes in citrulline contents and the expression of its metabolic genes were analyzed during the fruit ripening of two watermelon varieties and both of them were grafted onto pumpkin with the aim to study the differences of citrulline content and gene expression in citrulline biosynthesis between two varieties.By this,we can also examine the effects of grafting on citrulline content and the changes of gene expression of citrulline biosynthesis during fruit development between different watermelon varieties.In this study,high performance liquid chromatography(HPLC)and spectrophotometric method(UV)were compared to find a more accurate and convenient meththod to determined the content of watermelon.The results showed that to the same watermelon samples,the data of two methods had a good consistency.Through the analysis and evaluation about the citrulline content in watermelon germplasm resources,found that the citrulline content of 195 watermelon germplasm resources ranged from 0.49 g/kg?FW to 2.55 g/kg?FW.The citrulline concents of brightly flesh color watermelon(yellow,pink,red)were significantly higher than white flesh ones;the citrulline contents of the landrace watermelon cultivars,bred watermelon cultivars and cultivars from foreign countries were significantly higher than wild watermelon,egusi watermelon and edible seed watermelon.Comparison of the citrulline content of watermelon in different ecological condition,the results showed that the citrulline content of watermelon in Henan Proveince was higher than that in Hainan Province,the citrulline content of watermelon was effected by environment.And ‘9904’ and ‘SBD black’ were selected for further study.On the other hand,comparison the difference of citrulline content in watermelon fruits during fruit development between diffetent varieties,found that the citrulline content in the watermelon flesh gradually increased with fruit development and reached the highest level near ripening then gradually decreased as ripening proceeds.The citrulline content in ‘9904’ was higher than that in ‘SBD black’,and the difference was larget.Grafting onto pumpkin can increase citrulline contents in watermelon fruit and the effects of grafting on citrulline content was varied with the different varieties.The gene expression related to citrulline biosynthesis in ‘9904’ and ‘SBD black’ during fruit development,suggested that ASS2 expression level plays an important role in the citrulline synthesis pathway and ASL1 and ASL2 expression level work together to regulate the citrulline content.The differences of the citrulline content between ‘9904’ and ‘SBD black’ attributed to the high expression of the upstream genes NAGS,NAGK,GAT and OTC,the low expression of the downstream genes ASS2,ASL1,ASL2 and Arginase in ‘9904’.The expression level of NAGS,NAGK,ASS2,ASL1 and Arginase play an important role in the citrulline biosynthesis.The pumpkin rootstock of grafting can regulate the expression of genes involved in the citrulline biosynthesis ultimately regulating citrulline content.