Formation et distribution de glace dans les bourgeons de Vitis vinifera avant et au cours de leur débourrement

Evolution of the exothermic profile of latent buds of Vitis vinifera L. cv. Pinot noir was followed using differential scanning microcalorimetry. Analyses performed on buds at the winterized state (stage 1), on wolly buds (stage 3), and on green pointing buds (stage 5) showed that modes and speed of extracellular and intracellular liquid crystallisation vary according to the phenological stage and are closely linked to the meristematic tissues. Among these, the vascular system plays a major role in the crystallisation process. Indeed, within the winterized buds, where it is at the procambial stage, i.e. nonfunctional, it forms a barrier to the propagation of ice toward the apical part of the bud where water remains in a prolongated surfusion state. On the opposite, during the period preceeding bud opening, from stage 3 to stage 5, where its differentiation leads to a continuous and functional vascular system connecting the bud base to its apical part, it forms a preferred path allowing rapid ice propagation, leading to a violent ice setting in all the tissues. Key words: latent bud, exotherm, calorimetry, vascular system, wine. [Journal translation]