The evolution of the Ca++ content in the various compartments can vary from year to year or with the grapevine cultivar (Cabanne and Doneche 2001). It appears that the Ca++ content of the pericarp increases until veraison, then decreases during ripening (Cabanne and Doneche 2003). At veraison, rupture of the xylem vessels occur in the pericarp and this is probably responsible for the halt of Ca++ accumulation in this compartment (Düring et al. 1987). On the other hand, our results show that Ca++ accumulation was not observed in the flesh nor in the seeds, contrary to what was observed for the skin during the post-veraison phase, in both water status treatments (Fig. 4b1,b2,b3). According to Doneche and Chardonnet (1992), there is a dramatic reduction in the concentration of Ca++ in cells of the flesh, whereas it is abundant in the skin area.
In Grenache noir berries, the seeds were the smallest sink for the Ca++. It was accumulated into the seeds of the berry prior to veraison, not during ripening. Moreover, Cabanne and Doneche (2003) and Rogiers et al. (2006b) reported that the seed's Ca++ content increases during ripening in several other grape varieties (Cabernet Sauvignon, Semillon, Merlot, Sauvignon and Syrah). In the pre-veraison phase, xylem tracer studies indicated that xylem flow occurred along not only the bundles supplying the skin and flesh of the berry, but also the central bundles leading to the seeds (Rogiers et al. 2001), again suggesting continuous xylem flow to the seeds. During the post-veraison phase, however, the xylem tracers were limited to the brush region of the central bundles (Düring et al. 1987, Findlay et al. 1987, Creasy et al. 1993, Rogiers et al. 2001).
The metabolism of the grape berry is now known to be a complex process where considerable compartmentalisation occurs between different types of tissues (Famiani et al. 2000). The Ca++ content and its evolution must be considered in the same way (Cabanne and Doneche 2003). Indeed, while Ca++ accumulation ceases at the onset of ripening in the flesh and seeds, it persists in the skin. At the same time, Ca++ is probably translocated to skin cells during ripening by apoplastic and/or symplastic movement or by partial functioning of the xylem after veraison.
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