Stachyose Catabolize Location And Relationship With Six Forms Of α-galactosidases In Cucumber Fruit

Transportation and discharge of photosynathate in fruit is the material basis for the production and quality of fruit vegetables.Cucumber(Cucumis sativus L.)is an important crops of Cucurbitaceae and uses stachyose in raffinose family oligosaccharides(RFOs)as the main form of photosynthate.However stachyose through the phloem long distance after transport in the cucumber which part of the decomposition is not yet clear.α-galactosidase(EC 3.2.1.22)is a key enzyme for the catalytic of stachyose.In the cucumber genome,there are three acidic a-galactosidases and three alkaline a-galactosidases respectively,but which one plays a major role in the decomposition of stachyose is not clear at present.These status has seriously restricted the development of high quality cultivation and breeding theory of Cucurbitaceae.In this study,the structure of vascular bundles in cucumber peduncle and fruit was observed by optical microscope.The contents of five soluble sugars from phloem sap and tisseus in different ecotypes of cucumber stem,peduncle and fruit were studied.At the same time the relative expression of six a-galactosidase genes in different parts of cucumber were studied by qPCR and in stiu hybridization technology,and the result was verified by study of melon.In order to explore the exact discharding sites and enzymes of stachyose in cucumber,and to provide a theoretical basis for the development of new strategies for high yield and quality cultivation and breeding of cucumber.The results showed that:1.There were bicollateral vascular bundle structures in the cucumber peduncle and fruit.And there three vascular systerms in th fruit,a layer of vascular bundles neer the pericarp,10 main vascular bundles and a layer of vascular bundles around the placenta,known as periphery vascular bundle,carpel vascular bundle and placenta vascular bundle respectively in this study,Moreover,it also exited irregular distribution with bits of small vascular bundles in the cucumber pulp tissues.2.The content of stachyose and raffinose in vascular bundles of north china type "Jinchun 5",Europe-type "8316" and oriental pickling melon(Cucumis,melo L.var.conomon Thunberg.)were higher than those in the non-vascular bundles.Indicating that the vascular bundles was the main place where stachyose was catabolized.Stachyose was present in the three layer vascular bundles,but the content of stchyose in carpel is significantly higher than that in the other two vascular bundles.These results indicated that the decomposition of stachyose is mainly carried out in the carpel vascular bundle.3.The contents of stachyose and raffinose in phloem sap and the tissues of three vareites from peduncle to the end of fruit were gradually decreased.The result indicated that stachyose was catabolized gradually from the cucumber peduncle to the end of fruit.4.All kinds of a-galactosidase genes were expressed in peduncle and fruit of cucumber.The relative expression of alkaline a-galactosidase II in the carpel vascular bundle was higher than the other two,and in the three vascular system was higher than in the corresponding non-vascular parts.The results showed that the content of stychyose in fruit was only significantly correlated with the relative expression of alkali a-galactosidases II.but not with the expreesion of the other.5.In situ localization of three alkaline a-galactosidase mRANs in cucumber peduncle and fruit showed that the expression of the alkaline a-galactosidase Ⅱ was higher than the other two.With the result of 4.it showed that alkaline a-galactosidase Ⅱ maybe the main enzyme for the decomposition of stchyose in cucumber fruit.