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Sugar Transport in Immature Internodal Tissue of Sugarcane

I. Mechanism and Kinetics of Accumulation ¹

^a Department of Plant Physiology, Hawaii Agricultural Experiment Station, University of Hawaii, Hilo, Hawaii 96720

Transmembrane sugar transport into immature internodal parenchyma tissue of sugarcane (Saccharum officinarum L.) is a metabolically regulated process as evidenced by its sensitivity to pH, temperature, anaerobiosis, and metabolic inhibitors. All sugars studied—glucose, fructose, galactose, sorbose, glucose 6-phosphate, 3-O-methylglucose, and 2-deoxy-D-glucose—were apparently transported via the same carrier sites since they competed with each other for uptake. External concentrations of these sugars at one-half V_max were in the range of 3.9 to 8.4 nM. Preliminary data indicated that phosphorylation may be closely associated with glucose transport. The dominant intracellular sugar after 4-hours incubation was sucrose when glucose, glucose-6-P, or fructose was the exogenously supplied sugar; but when galactose was supplied, only 28% of intracellular radioactivity was in sucrose. Sorbose, 3-O-methylglucose, and 2-deoxy-D-glucose were not metabolized. Thus, by using these analogs, transport could be studied independently of subsequent metabolism, effectively eliminating a complicating factor in previous studies.