Christel Marquat

Dormancy in vegetative buds of peach : relation between carbohydrate absorption potentials and carbohydrate concentration in the bud during dormancy and its release

The absorption of sucrose and sorbitol by the bud and the stem of Prunus persica was evaluated during the rest period. The utilization of p-chloromercuribenzenesulfonic acid (PCMBS), an inhibitor of sucrose transporter, allowed estimation of the active absorption of sucrose in different isolated organs (bud, buds underlying tissues and stem). It was assumed that the sink capacities of tissues depended on their potential to absorb carbohydrates by active transport. Endogenous carbohydrate levels in the tissues were also measured. In the bud, the qualitative and quantitative distribution of carbohydrates could be related to the absorption potential of the bud. During dormancy, the bud exhibited a low absorption potential and increased its sucrose concentration by starch hydrolysis. Soluble sugars accumulated during winter. During dormancy release, the bud was able to absorb carbohydrates allowing carbon storage. The data presented led to the proposal of a scheme of events occurring during bud dormancy and its release.

Saccharose and sorbitol transporters from plasmalemma membrane vesicles of peach tree leaves

The mechanisms of saccharose and sorbitol transport in Prunus persica leaves were investigated in plasma membrane vesicles purified by aqueous 2-phase partitioning and equilibrated in pH 7.5 buffer containing K+. The imposition of an artificial proton motive force energized an active uptake of both saccharose and sorbitol. The maximum uptake rate of saccharose was 2.5 times higher than that of sorbitol. Saccharose and sorbitol uptake exhibited saturation kinetics suggesting they were carrier-mediated. Apparent Km for the saccharose and the sorbitol uptake were 0.36 and 0.67 mM, respectively. Active absorption of saccharose was completely inhibited by a non-permeant thiol reagent, PCMBS, contrary to sorbitol absorption. These results suggested that saccharose and sorbitol were transported at least by two different carriers.

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

Summary 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 the 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 cuttings. In natural conditions, three periods were disclosed: 1) from September to October, the 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.