Study of H+-nutrient co-transport in peach-tree and the approach to their involvement in the expression of vegetative bud growth capability

Sucrose and sorbitol are the predominant forms of photosynthetically reduced carbon transported in Prunus persica. The mechanisms of sucrose and sorbitol transport were investigated in plasma membrane vesicles isolated from peach tree leaves. The maximum uptake was obtained for sucrose (2.5 times higher than sorbitol uptake). Active absorption of sucrose was completely inhibited by a non-permeant thiol reagent, PCMBS, contrary to sorbitol absorption. These results suggested that sucrose and sorbitol were transported at least by two different carriers. The absorption of exogenous sucrose and sorbitol in the bud and the underlying territories of the bud and their distribution in the single node cuttings were evaluated during the vegetative rest period. The utilization of PCMBS, an Inhibitor of sucrose transporter, allowed for the estimation of rhs active absorption of sucrose in different isolated territories. It was assumed that the sink capacities of tissues depend on their potentialities to absorb carbohydrates by H+/symport. The presence of unlabelled sucrose during PCMBS pretreatment decreased the inhibition exerted by PCMBS: it suggested that the inhibitor was bound specifically on the sucrose transporter. The ''active'' absorption related to the transporter could therefore be distinguished from the total absorption, including diffusion. The evolution of exogenous sucrose and sorbitol was evaluated during the vegetative rest period, in isolated territories and in single node cut tings. In natural conditions, three periods were disclosed: 1) from September to October, bud, intrinsically able to grow, was inhibited by the stem; 2) from November to December the bud was in a state of deep dormancy, and it was intrinsically unable to absorb nutrients; and 3) January was characterized by the reacquisition of bud growth potential and bud burst. Concerning sorbitol, a similar evolution was observed but it seemed that sorbitol was principally utilized a few days before budburst.