Absorption of Sugars by Plant Tissues

Abstract

There is already evidence that processes other than simple diffusion contribute to the uptake of sugars by some plant cells. For example, the preferential absorption of particular sugars by Scenedesmus (21,22), Peltigera (12), and tomato roots (8), and the effects of metabolic inhibitors on uptake (5,11,15) are well established. Moreover, accumulation against apparent concentration gradients has been shown for sugar cane tissue (4) and the ability of carrot tissues, rich in sugar, to take up all of the glucose from dilute glucose solutions is of interest (9).Nevertheless, on the basis of the present information, it is not possible to draw general conclusions about transport against gradients (15) or to make deductions about the mechanism of transport. In this paper experiments with carrot slices and corn root tips are described in which the abilities of these tissues to absorb different monosaccharides, the effects of other sugars and inhibitors on the absorption process, and the responses to anaerobiosis and temperature were measured. Internal concentrations of entering sugars have been determined to test if active transport against a gradient occurs and some deductions are made about compartmentation of sugars in these 2 tissues. Materials and MethodsPlant Tissue. Carrots were purchased as required from the local market and stored briefly in the refrigerator until used. Cylinders were cut from the secondary phloem tissue with a cork borer (diameter 6 mm) and sliced into discs approximately 1 mm thick. Discs described as fresh were sliced into ice cold water, rinsed twice with deionized water, and dried lightly on paper toweling. Weighed samples were then taken for uptake experiments. Washed discs were prepared by cutting tissue into a large volume of water which was then aerated at room temperature by a stream of air for 24 hours. These were then dried and sampled in the same way as the fresh discs.Corn

The Regulation of Sugar Uptake and Accumulation in Bean Pod Tissue

“…In botlh carrot root anid corn root tissue L-arabinose and D-ribose are accumiulated as such (8). In bean endocarp L-arabinose and D-ribose (table V) do not inhibit fructose uptake over a vide range of concentratioins.…”

Multiphasic Absorption of Glucose and 3-O-Methyl Glucose by Aged Potato Slices

“…Grant and Beevers describe an absorption process which is putatively a smooth hyperbolic function of concentration with an apparent Km of approximately 10 mm. Laties, on the other hand, finds uptake to be virtually zero-order at concentrations approaching 10 yM. Both studies report uptake against a gross concentration 'The work herein generously was supported by a grant from the United States Atomic Energy Commission.…”

“…Significant questions which persist regarding the process of glucose absorption in higher plant tissues are best revealed by a comparison of the observations of Grant and Beevers (10) on glucose absorption by carrot slices and of Laties (15) on glucose uptake by potato discs. Grant and Beevers describe an absorption process which is putatively a smooth hyperbolic function of concentration with an apparent Km of approximately 10 mm.…”

“…Sugar transport has been taken to be carrier-mediated on the basis of studies in yeast (13), red blood cells (17), intestinal epithelial cells (2), muscle fibers (9), algal coenocytes (23), and higher plant cells (10). The deduction has been based both on the specificity of the process and on the generally observed hyperbolic absorption isotherm.…”

Uptake of Amino Acids and Other Organic Compounds by Lemna paucicostata Hegelm. 6746

“…Reciprocal inhibition studies strongly support the conclusion that o-glucose, D-galactose, and D-mannose are taken up by the same system. Previously, Grant and Beevers (10) reported that uptake of galactose by carrot slices and corn root tips was inhibited by glucose, but that uptake of glucose was not inhibited by galactose. For immature internodal tissue of sugarcane, Bowen (2) found mutual inhibition between galactose and glucose, and the K, for galactose agreed closely with its Km.…”