Effects of ABA on the distribution of sucrose and protons across the plasmalemma of pea mesophyll protoplasts.-Suggesting a sucrose/proton symport.

摘要

A study was made of the effects of 10-9-10-6 mol abscisic acid (ABA)/litre on light-induced CO2-dependent O2 evolution, sucrose synthesis, efflux of sucrose and changes in cytosolic proton concentration in mesophyll protoplasts of peas cv. Fenomen.Photosynthesis did not change with increased apoplastic ABA or sucrose concentrations although sucrose synthesis decreased in the presence of ABA. In the absence of apoplastic sucrose the sucrose efflux increased and was most pronounced at 10-7 mol ABA/litre. The sucrose efflux also increased in the presence of ABA + sucrose and was most pronounced at 10-9 mol ABA/litre and 20 mmol apoplastic sucrose/litre. The cytosolic proton concentration decreased upon addition of ABA with or without sucrose, but increased upon addition of p-chloromercuribenzenesulfonic acid, a sucrose transport inhibitor. The cytosolic proton concentration decreased in the presence of 10-9 mol ABA/litre in combination with various apoplastic sucrose concentrations. In the presenceof 10-7-10-6 mol ABA/litre in combination with apoplastic sucrose levels higher than 1 mmol/litre, the cytosolic concentration of proton increased. These results indicate that there is a relationship between the external environment and the sucrose efflux and cytosolic proton concentration in pea mesophyll protoplasts and that there is a sucrose/proton symport at the plasmalemma of pea mesophyll cells. They also show that sucrose increases the sensitivity to ABA in its action on sucrose efflux and cytosolic proton concentration.