Sucrose Uptake by Sugar Beet Tap Root Tissue

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Abstract
Sucrose uptake by discs of mature sugar beet [Mono Hy-D2] root tissue incubated in [14C]-sucrose exhibited nonsaturating kinetics over the concentration range of 1-500 mM. Uptake was inhibited by dinitrophenol, NaCN, low O2, and penetrating sulfhydryl inhibitors. ATPase inhibitors, NaF, and oligomycin reduced uptake by 20 and 40%, respectively. Uptake as asymmetrically labeled sucrose ([14C]glucose) occurred with approximately 80% retention of asymmetry, indicating a nonhydrolytic pathway. Uptake was against a concentration gradient and required metabolic energy. Glucose and fructose uptake exhibited typical saturation kinetics but rates of uptake were lower than that of sucrose, particularly at high concentration. Glucose strongly inhibited the uptake of sucrose and fructose but sucrose and fructose had little effect on the rate of glucose uptake. A major portion of the sucrose movement between its free space and vacuole probably occurs via a nonsaturating carrier at sites where the plasmalemma and tonoplast are appressed.