Differential Rates of Uptake of Glucose, Fructose and Sucrose by Pea Stem Protoplasts

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Abstract
Protoplasts from growing regions of etiolated pea stems take up glucose more rapidly than fructose when supplied for brief periods at low concentrations. The uptake of the two hexoses is differentially inhibited by galactoac and by reagents that curtail ATP synthesis, and uptake of one hexose is not prevented by the other, even at a 100-fold excess. Sucrose uptake is much slower than that of either hexose and is correlated with the appearance of invertase activity in the medium. Label from [14C-glc]-sucrose is taken up more rapidly than from [14C-fru]-sucrose. It is concluded that these cells take up supplied sucrose only after hydrolysis to hexoses, which are then absorbed by different carrier-mediated processes.