Sugar Transport and Sulfite Action in Etioprotoplasts, Semi‐Etioprotoplasts and Green Protoplasts of Avena sativa L.

Abstract

AbstractThe mechanism of glucose and sucrose transport and the influence of various concentrations of sulfite on its activity was studied in mesophyll protoplasts (etioprotoplasts, semi‐etioprotoplasts and green protoplasts) isolated from oat (Avena sativa L.) seedlings.Kinetic analysis of [14C] glucose loading (in darkness) revealed in each kind of protoplasts the presence of two transport components. At low exogenous glucose concentrations a saturable system was the main mode of transport. At concentrations higher than 20 mM the loading of glucose in all types of protoplasts was dominated by a non‐saturable, linear diffusion‐like component. The rate of glucose uptake was greatest in etioprotoplasts and lowest in green protoplasts.In contrast to the above we have not found saturable components of sucrose transport in any kind of protoplasts. The rate of its uptake was greatest in semi‐etioprotoplasts.Sulfite, at a concentration of < 1.0 mM stimulated and at ≥ 1.0 mM inhibited the uptake of glucose to etioprotoplasts and semi‐etioprotoplasts and inhibited that to green protoplasts at any concentration. The transport of sucrose underwent a significant inhibition in the various types of protoplasts only under the influence of 10.0 mM of sulfite ions.Inhibition of glucose uptake by sulfite was of the non‐competitive type.Sulfite also affected the level of adenylic nucleotides and lowered the energy charge and ATP/ADP ratio.Intensity of sulfite uptake was significantly higher in green protoplasts than in etioprotoplasts.