Mechanism of sugar accumulation into vacuoles to improve the fruit quality

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The purpose of this project is to make clear the mechanism of sugar accumulation in fruit tissue or cells.1. Cellular compartmentation of sugars : We investigated the localization of sugars and the change of their contents in fruit. More than 70% of sugars distributed in the vacuole and others in the apoplast in strawberry and melon fruits. With fruit maturation, the palsma membrane became leaky to sugar penetration, resultantly the sugar content in the apoplast increased.2. The mechanism of sugar transport across the membrane and its stimulation by plant hormones : There present 2 types of carrier-mediated and simple diffusional transports to the uptake of sugars into cells. In strawberry and melon fruits, we detected the carrier-mediated transport of sucrose, glucose and fructose in young fruit, but the carrier-mediated transport of sucrose disappeared during fruit maturation. IAA stimulated the sugar uptake via the carrier-mediated transport. On the contrary, ABA stimulated the sugar uptake via the simple diffusional transport. This may be caused by the stimulation of sugar uptake into the vacuole.3. The role of vacuolar H^+-ATPase and H^+-PPase : V-H^+-ATPase and V-H^+-PPase were prepared from the tonoplast vesicles of pear fruits, and their roles were compared each other through the developmental stage. H^+-PPase activity was higher in young fruit and H^+-ATPase activity became higher with fruit maturation.4. Sugar transport mechanism into the tonoplast vesicle : We make clear the participation of carrier protein of facilitated diffusion of glucose and fructose in the tonoplast vesicles.