SUCROSE METABOLISM IN MANGO FRUIT DURING RIPENING

The amounts of sucrose, starch, fructose and glucose were determined in ripening mango fruits (cv. Haden) grown in Venezuela. Samples were taken at two-day intervals, over a ripening period of 16 days commencing 90 days after flowering. The level of sucrose increased rapidly after day 6 and then remained high. The amount of starch decreased slightly during the ripening period but was insufficient to account for the observed increase in the level of sucrose. Reducing sugars, comprising mainly of fructose, increased slightly during ripening. Sucrose phosphate synthase activity increased about 10-fold during the phase of rapid sucrose accumulation. This activity was more than sufficient to account for the maximum observed rate of sucrose synthesis. The proportion of sucrose phosphate synthase activity that was sensitive to inhibition by inorganic phosphate changed during ripening. Maximum catalytic activity of sucrose synthase remained constant throughout the ripening period and was sufficient to contribute significantly to sucrose metabolism. The activities of neutral and acid invertases were very low in comparison with those of the other enzymes of sucrose synthesis. However, acid invertase activity did increase and later decrease during ripening.