Changes in Soluble and Transported Sugars Content and Activity of Their Hydrolytic Enzymes in Muskmelon (Cucumis melo L.) Fruit During Development and Senescence

A temporal relationship between changes in soluble sugar content and the activity of their hydrolytic enzymes of netted melon fruit during development and senescence was investigated. Analysis for the sugars content of the commercial cultivars ‘Sunpower’ and ‘MVP’ revealed the major soluble sugars in pulp tissue of melon fruit were sucrose, glucose, fructose. In addition, raffinose and stachyose were also found during the ontogeny of the fruit. During a rapid fruit growth, up to 30 days after pollination (DAP), the amount of sucrose, raffinose, and stachyose remained substantially low, ranging from 0.0 to 0.1 miligram per gram fresh weight. However, the level of fructose and glucose maintained relatively high in the tissue, ranging 10 to 25 miligram per gram fresh weight. In accordance with this result, the activity of both acidic and neutral invertase showed a fairly high upto 20 DAP, and followed by a sharp decrease in the activities during maturation and senescence of the fruit. A similar pattern of the change in the activity of both acidic and neutral ɑ-galactosidase also observed during the fruit development and senescence. Concomitantly to this, there was a rapid increase in the pool size of sucrose, raffinose, stachyose, substantiating an increase in soluble sugar contents in the aging fruit. From the present study, it was suggested that in netted melon fruit both invertase and ɑ-galactosidase play an important role in regulating the accumulation of the soluble sugars, which, in turn leads to an increase sweetness of the fruit.