Energy Coupled Transport of Sorbitol and Other Sugars into the Protoplast Isolated from Apple Fruit Flesh

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The uptake kinetics of sorbitol, sucrose, glucose and fructose across the plasma membrane using protoplasts isolated from apple fruit flesh (Malus pumila Mill. var. domestica Schneid.) was investigated. When sorbitol was taken up into the cell, PCMBS-sensitive saturable transport was distinguishable from the diffusive transport. At a low sorbitol concentration, the saturable transport system accounted for more than 50% of the total uptake, whereas at a high concentration the diffusive transport system was more dominant. The saturable transport was suggested to be a carrier-mediated transport system coupled with ATP because the system was inhibited by CCCP or orthovanadate. The K_m value for sorbitol was computed to be 3.6 mM. A carrier-mediated transport system coupled with ATP was also observed for glucose and fructose with a corresponding K_m values of 5.0 and 2.5 mM. However, no saturable transport for sucrose was observed over a range of 0.1 to 10 mM sucrose concentration. The relationship among these sugar transport systems across the plasma membrane, apoplastic unloading, and sugar accumulation in vacuoles are discussed.
日本植物生理学会の論文