Influencia del riego en las células tánicas del hollejo de "Vitis vinifera" L. cv Tempranillo

The localisation and shape of phenolic compounds in grape skin are influenced by reactions during grape maturation. The study of changes that occur in grape cells is essential to understand the pigment diffusion process in winemaking. The target of this study was to determine the influence of irrigation on the evolution of tannic cells in grape skins 'Tempranillo' during ripening. The study was carried out in an experimental vineyard located in the Research Centre La Orden-Valdesequera during campaign 2011. Treatments consisted of: non-irrigated vines (C) and a full irrigation treatment to cover 100% of crop water needs throughout the campaign (R). Cross-sections of berries collected at several stages of grape ripening were fixed in a solution of formalin, acetic acid and ferrous sulfate which provides a dark coloring to tannins. Samples were included on paraffin and sections of 12 μm were obtained. Then, sections were stained with phloroglucinol-HCl. In the grape skins, it has been distinguished two main kinds of cells: cells without phenolic compounds (without colour) and cells containing phenolic compounds (tannic cells). According to the polymerization degree of these tannic compounds cells have been classified into: (a) with uniform coloring; (b) cells with fine granules evenly distributed; (c) with small spherical inclusions united to the tonoplast or free in the vacuole, and (d) with large inclusions. We studied the effect of maturation and irrigation in the percentage of the different cells of the skin. During maturation it has been observed a decrease in the number of cells of the type b and an increase in the type d, in both treatments. Regarding the treatments, it was noted that at vintage (115 dpf), the irrigation produced a percentage significantly smaller of both cell types without coloration and with large inclusions, and a higher percentage of cells with uniform coloration. This indicates that irrigation influences the amount and distribution of the cells of the skin.