Anatomical, histological, and histochemical changes in grape seeds from Vitis vinifera L. cv cabernet franc during fruit development

Cabernet franc berries were sampled at five stages from berry set to harvest from an experimental vineyard in mid Loire Valley. Seeds were collected from representative berries in term of stage of development. The evolution of seed was followed both macro- and microscopically. For microscopy analysis, seeds were cut, put in a fixation solution, and cut into thin sections with a microtome. Five staining solutions were used for each seed sample: toluidine blue O, phloroglucinol, periodic acid-Schiff's reagent and naphtol blue black, vanillin, and p-dimethylaminocinnamaldehyde. Toluidine blue O staining revealed the evolution of tissue structures during grape seed development. We studied the changes in chemical compounds (lignin, polysaccharides, proteins, and tannins) with the other reagents. Seed lignification was achieved at veraison. Proanthocyanidins were localized in epidermis, inner cells of the soft seed coat, and inner cell layer of the inner integument. Finally, the localization of flavan-3-ols was linked with changes in cell walls of the outer integument.