Determinations on the sugars and ascorbic acid content of Bai-Lan melons were made during fruit development and ripening periods. Changes in the intensities of sucrose synthesis and hydrolysis of fruits and leaves of different ages were also measured by the vacuum infiltration method.
Total sugars increased continuously throughout the growing period, but the rate of increment was much accelerated during the ripening period of the fruit. The maximal content of total sugars, which ranged from 6.68% to 8.07% on a basis of fresh weight, was observed at full maturity. The variation of starch content followed a similar course as did the total sugars.
During the early stages of fruit development, there was a steady increase in reducing sugars, whereas the amount of sucrose was insignificant. After the first 30 days of fruit development, when the enlargement of fruit size was almost completed, however, a gradual decline in reducing sugars anti a concomitant rapid increase in sucrose were noted. The maximal concentration of sucrose, which constituted more than 70% of the total sugars of mature fruit, was attained at the time of full maturity. Changes in the concentrations of glucose and fructose were similar to that of reducing sugars, but the percentage of glucose was usually higher than that of fructose.
It was found that the enzymatic hydrolysis of sucrose was predominated over the synthetic process in young, actively growing fruits. However, the direction of the enzymatic reactions changed in favor of the synthetic process during the ripening period of the fruit. On the other hand, the ratio of synthesis/hydrolysis of sucrose in leaves was changed from a high to a low value during the period of ageing. The significance of these findings in sugar accumulation of fruits and in the interdependence of physiological functions between leaves and fruits is discussed.
The concentration of ascorbic acid decreased from the beginning of the fruit growing period, reached a maximum at about 30 days after blossoming, and then increased rapidly until maturity.
The importance of the results in determining the proper stage of maturity for picking of Bai-Lan melons is indicated.