Effect of abscisic acid (ABA) on sugar accumulation in the flesh tissue of peach fruit at the start of the maturation stage

Experiments were conducted on C-14-sorbitol, fructose, and glucose uptake into flesh discs, and sorbitol efflux from the discs, with and without ABA application to examine the effect of abscisic acid (ABA) on sugar accumulation in peach fruit flesh at the start of the maturation stage in relation to membrane transport. Total uptake of C-14-sorbitol, fructose, and glucose into flesh discs was effectively promoted by ABA at a concentration of 10(-5) M. PCMBS (p-chloromercuribenzensulfonic acid)-sensitive uptake, which was considered as carrier-mediated uptake, of sorbitol into the discs was clearly stimulated by ABA at 10(-5) M, compared with glucose and fructose uptake. Sorbitol efflux from the discs across the tonoplast was restricted by ABA at 10(-5) M. ABA application to developing fruit increased sugar accumulation in the fruit. Estimated ABA concentration in this fruit was approximately 10(-5) M. These results indicate that sugar accumulation in peach fruit flesh is stimulated by ABA at a concentration of 10(-5) M both in vitro and in vivo. ABA stimulates uptake of sugars, especially sorbitol, into the flesh by enhancing carrier-mediated transport possibly across both tonoplast and plasma membrane.