A Study On RFOs Catabolize Location And Relationship With Acidic、Alkaline α-galactosidases In Fruit Of Cucumber (Cucumis Sativus L.)

Unlike most higher plants, cucumber (Cucumis sativus L.) transports raffinose family oligosaccharides (RFOs) (primarily stachyose and raffinose) as the main form of photosynthate. After long distance transportation, stachyose reaches the fruit. However the catabolizing location of stachyose is unclear in fruit. One view is that stachyose catabolized into sucrose in pedicel and then transported to the fruit; the other is that stachyose flows through the pedicel, fastly catabolized in fruit. Alpha-galactosidase plays an important role in stachyose catabolism. There is no unified view that which kind or which one plays a main function when stachyose catabolized by six alpha-galactosidase (three alkaline forms and three acidic forms). In this study, contents of soluble sugars in phloem sap were determined in cucumber fruit pedicel, fruits and melon fruit pedicel. At the same time, contents of soluble sugar, expression levels and activities of six alpha-galactosidase were investigated in cucumber pecdicel, fruit-front end and first fruit pedicel after the second fruit removed. We used a special chemical inducing expression vector pX6/pX7 to construct RNAi of two alkaline alpha-galactosidase for the later cucumber transgene reseach. The results were as follows:1、Stachyose and raffinose are catabolized in Cucumber pedicel and fruit, catabolized persistently. From cucumber pedicel to fruit, the contents of stchyose and raffinose in phloem sap were gradually decreased and drop to the lowest at the end of fruit. While sucrose, fructose and glucose were gradually increased. In conclution, contents of soluble sugar from pedicel to fruit were changing all the way, but slowly.2、Alkaline alpha-galactosidase plays a main role in cucumber fruit stachyose unloading. Six alpha-galactosidase gene expression levels, activities and contents of soluble sugar were studied in fruit pedicel and fruit front-end subsection. The results showed that contents of stachyose and raffinose were in contrast with the alkaline alpha-galactosidase expression levels and activities,but had no any obvious relation with acidic alpha-galactosidase. After removing the second fruit, contents of soluble sugar in first fruit pedicel tissue and sap, expression levels and activities of six alpha-galactosidase were studied. It showed that alkaline alpha-galactosidase gene expression levels and activities increased consistently. However, acidic alpha-galactosidase did not has the corresponding trend.3、Melon fruit pedicel exists stachyose catabolism. Contents of raffinose and stachyose in melon pedicel sap were gradually decreased from stem to fruit. While sucrose, glucose and fructose were gradually increased.^Successfully builded RNAi vectors of alkaline alpha-galactosidase Ⅰ and Ⅱ. RNAi vectors of two alkaline alpha-galactosidase were constructed using a special chemical inducing expression vector pX6/pX7. Determined by electrophoresis detection and sequencing. It could be used in the later cucumber transgene research.