Evolution of the localisation and composition of phenolics in grape skin between veraison and maturity in relation to water availability and some climatic conditions.

Background: Several studies have investigated the composition of phenolics in grape skin during grape maturation under various conditions of light exposure, water stress, nitrogen supply and mineral nutrition, but their localisation during berry development is not well known. In this study the composition and localisation of proanthocyanidins were monitored for three years on four plots known to induce a distinctive behaviour of the vine (Cabernet Franc). The composition of phenolics was determined by spectrophotometry; also, in one year, proanthocyanidins were determined by high-performance liquid chromatography. Further information was obtained histochemically by means of toluidine blue O staining and image analysis.

Results: The results indicated that clear differences in phenolic quantification existed between the biochemical and histochemical approaches; the proportion of cells without phenolics was not linked with the quantity determined by the analytical methods used. The histochemical method showed the evolution of the localisation and typology of cells with and without phenolics during ripening. The number of cells without any phenolic compounds appeared to be very dependent on the mesoclimatic conditions and only slightly dependent on the site water status.

Conclusion: Clear differences in phenolic quantification existed between the biochemical and histochemical approaches; the proportion of cells with phenolics was not linked with the quantity determined by biochemistry. The histochemical method showed an evolution of the localisation and typology of cells with and without phenolics in which mesoclimatic conditions were the most influential factor. Finally, the study showed some advantages of the histochemical approach: it gives information about the anatomy of the tissue as well as the nature and distribution of some of the large macromolecules and allows reconstruction of the three-dimensional plant structure.