Absorption of Sugars by Plant Tissues

Abstract

The uptake of C14 labeled D-glucose, D-fructose, D-galactose, D-xylose, D-and L-arabinose and D-ribose by excised carrot discs and corn roots was investigated. Glucose uptake was increased more than 10-fold by increasing the temperature from 3[degree] to 25[degree], and witholding oxygen strongly depressed the uptake of glucose, fructose, galactose and xylose. Carrot discs removed virtually all of the glucose-C14 or fructose-C14 from 0.001 [image] solutions and did not release labeled sugars into the medium on subsequent incubation in water. For carrot discs the maximum absorption rates for the various sugars were between 3 and 10 micromoles/g hr and half-maximum rates were observed at concentrations between 0.5 and 23 x 10-2 [image]. Corresponding values for corn roots were 7-34 micromoles/g hr and 0.7-25 x 10-2 [image]. Glucose interfered competitively with the uptake of the other sugars. Internal sugar levels and conversion of added C14-labeled sugars to CO2 and other products were determined. Accumulation against apparent gradients was demonstrated for several sugars. In carrot, the respiratory CO2 was derived preferentially from entering glucose and fructose, demonstrating compartmentation of these sugars in vivo.