Southern Blot And Expression Analysis Of 4 α-galactosidases In Cucumber (Cucumis Sativus L.)

Stachyose is the major carbohydrate translocated by cucumber(Cucumis sativus L.)in the phloem, while sucrose, glucose and fructose are major carbohydrates in fruit. The initial step in stachyose catabolism is thought to be hydrolysis byα-galactosidase. To study the detailed mechanism of stachyose unloading in cucumber, we have cloned the full length cDNA sequences of two putative aicdα-galactosidases two putative alkaliα-galactosidases. In this study, Southern blot was used to identify the copy number of 4α-galactosidase genes in the cucumber genome, and the correlation of fruit growth and the mRNA expression of 4α-galactosidase genes in fruits and peduncles was investigated to study whichα-galactosidase is mainly responsed for stachyose catabolism in cucumber. The results showed that:1 For two acidα-galactosidase genes and alkaliα-galactosidaseⅠ, each restriction enzyme digestion yielded only one hybridising band, indicating that only one copy of each gene is present in the genome of cucumber. While for alkaliα-galactosidaseⅡ, each restriction enzyme digestion yielded two or three hybridising bands, indicating that this gene belongs to a small gene family in cucumber.2 The correlation between gene expression and the fruit growth of cucumber was investigated and the results showed that alkaliα-galactosidaseⅡmay play a key role in stachyose catabolism in cucumber fruit.