Changes in soluble sugar and activity of α-galactosidases and acid invertase during muskmelon (Cucumis melo L.) fruit development

Summary Soluble sugar, a-galactosidase (EC 3.2.1.22) and soluble acid invertase (EC 3.2.1.26) were determined in fruit tissues and peduncles of melon (Cucumis melo L. cv. Ranjadew) in the course of fruit development. Fruit development was followed from anthesis to fruit abscission (53-55 days after anthesis). At fruit maturity, the exo-mesocarp had the highest sugar content followed by endocarp and placenta, seeds and peduncles. Stachyose and raffinose were present in all fruit tissues and peduncles at all stages of development. Stachyose was the main sugar of the peduncles. In all other fruit tissues, sucrose and the hexoses prevailed. The sugar composition of phloem exudate collected from peduncles cut near stem or fruit was identical, indicating that translocate is conducted along the phloem of fruit peduncles unchanged. Acid invertase activity followed optimum curves, alkaline α-galactosidase activity declined and acid α-galactosidase slightly increased during fruit development, a-galactosidase and invertase activities are closely correlated with the distribution of raffinose oligosaccharides, sucrose and hexoses. Our data confirm a recent conclusion that raffinose oligosaccharides are translocated within the phloem into Cucurbit fruits and seeds and that oligosaccharides are effectively decomposed here by a-galactosidases.