Abstract: The conversions of incorporated 14C-glucose in fruit flesh and in seeds were investigated at different stages of fruit development. In addition, the biochemical mechanism of sucrose synthesis in fruits of Bai-Lan melon were also studied. The results were summarized as follows: In fruit flesh and in seeds at young fruit stage, more than half of the incorporated 14C was found in the dilute acid hydrolyzable and non-hydrolyzable fractions, both of which represent the structural elements. While in the fruits approaching maturity (42 days old), a relatively small amount of 14C associated with the structural elements was found. The contributions of 14C of fractions hydrolyzed and non-hydrolyzed by dilute acid to the total radioactivity were reduced to 18% and 32%, respectively, in fruit flesh and in seeds. The results of identification of soluable sugar by using paper chromatography indicated that, the 14C was only associated with fructose after infiltrating the young fruit slices with 14C-glucose, but the 14C was predominately incorporated into sucrose at later stage of fruit development. The above results of 14C labeling experiments suggest that the pattern of metabolism is changed with fruit development. The greater part of metabolites is used in synthesis of structural elements which is necessary for growth and related processes at early stage of fruit developrnent. However, as the fruit reaches full size. the demand for carbon used in structural tissue is reduced. At this time, the direction of the enzymatic reactions changed in favor of sucrose synthesis. The activity of sucrose synthesis in young fruits was rather low when various substrates were supplied. It was possible that the enzymes related to sucrose synthesis were absent in young fruits of Bai-Lan melon. The activity of sucrose synthesis in fruits at later stage of development increased by about 5-fold of that at early stage. The higher activity of sucrose synthesis was observed when UDPG+F-6-P were supplied as substrates. It is shown that the sucrose in Bai- Lan melon fruits may be mainly synthesized by sucrose phosphate synthetase catalyzing the reaction between UDPG and F-6-P to yield sucrose-P. The biochemical mechanism of sucrose synthesis in Bai-Lan melon fruits is briefly discussed.

Key words: Bai-Lan melon, Conversions of 14C-glucose, Sucrose synthesis