ON THE UPTAKE OF SUCROSE AND WATER BY FLOATING LEAF DISKS UNDER AEROBIC AND ANAEROBIC CONDITIONS

Abstract

It has long been known from feeding experiments that pieces of leaf may absorb sugar from solutions on which they are floated. Past work on this subject has been reviewed briefly in a previous paper (Weatherley, I954) in which measurements of sugar uptake by a number of species were reported, together with preliminary investigations on the nature of the uptake. It was suggested that sugar uptake by floating leaf disks is probably an active transfer rather than a passive absorption. If the transference of sugar from the external solution into the cells is an active, energy-requiring process, it would be expected that uptake would be reduced or stopped under anaerobic conditions. This present paper is devoted to a comparison of sugar uptake in aerobic with that in anaerobic conditions, and such a dependence of sucrose uptake on aerobic conditions is demonstrated. Attention is also paid to the changes in water-content of the leaf disks accompanying the uptake of sugar, and estimates made of the permeability constants of the tissues to water and sucrose. The data obtained are consistent with the hypothesis of a passive absorption of water following an active uptake of sugar. The experimental work was carried out at the Universities of Manchester and Nottingham. TECHNIQUE The uptake of sugar was measured as the increase in dry weight of samples of 30 to 40 leaf disks after floating on sugar solution. The details of this method, together with the procedure for collecting the samples, estimating the errors of sampling and treatment of the samples have been given in a previous paper (Weatherley, I954). As in that work attention was restricted largely to leaf disks of Atropa belladonna and to the uptake of sucrose, but in addition the water-content of the disks was measured simply by subtracting the dry weight of a sample from its fresh weight. To attain anaerobic conditions Petri dishes, containing the floating disks, were placed inside desiccators, each of which could accommodate two dishes. These desiccators contained about 200 ml. of alkaline pyrogallol and were fitted with inlet and outlet tubes so that after the Petri dishes had been placed inside, nitrogen could be blown through them to displace the air. The nitrogen, of chemically pure grade, was passed through a wash bottle also containing alkaline pyrogallol before entering the desiccators. After the air had been 'washed' out of the desiccators, they were clipped off and allowed to stand for