Abstract
Sucrose uptake by discs of mature sugar beet root tissue incubated in [(14)C]-sucrose exhibited nonsaturating kinetics over the concentration range of 1 to 500 millimolar. Uptake was inhibited by dinitrophenol, sodium cyanide, low O(2), and penetrating sulfhydryl inhibitors. ATPase inhibitors, sodium fluoride, and oligomycin reduced uptake by 20 and 40%, respectively. Uptake as asymmetrically labeled sucrose ([(14)C]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. It is proposed that a major protion of the sucrose movement between its free space and vacuole occurs via a nonsaturating carrier at sites where the plasmalemma and tonoplast are appressed.