Immunohistochemical localization of a putative flavonoid transporter in grape berries

Flavonoids are a class of secondary metabolites present in large amounts in grapevine (Vitis vinifera L.), which are involved in several aspects of its physiology (e.g. protection against biotic and abiotic stress). Even if the biosynthetic pathways of flavonoid sub-classes have been largely characterised, the mechanisms of their transport and accumulation to the final target sites are still not completely understood. Unanticipated insights have been obtained by probing plant tissues with pure antibodies targeting bilitranslocase (BTL, TCDB # 2.A.65.1.1), a mammalian transporter involved in the absorption and tissue distribution of dietary flavonoids. The occurrence of a BTL homologue has also been found in grape berries, in both tegumental layers of skin and pulp vascular bundles. In the skin, the expression of this protein starts from veraison (starting of the change in colour and softening of berries) and increases up to a maximum at the harvest stage, matching the same temporal pattern of flavonoid accumulation.