NOVEL FLAVONOID CARRIER IN WHITE GRAPE BERRIES: LOCALISATION AND FUNCTION

Up to date, it has been suggested that in grapevine (Vitis vinifera L.) berry the flavonoid transfer into the vacuole or to the cell wall requires primary (e.g. ABC-protein) or secondary (e.g. MATE-protein) active transporters. Recently, a putative flavonoid carrier, homologue to mammalian bilitranslocase (BTL) and able to perform a secondary active transport, was found in carnation petals and red grape berries. In this work, a BTL homologue has been shown in white berries from cv Tocai/Friulano. Similarly to that found in the red grape, the transporter exhibited a molecular mass of ca. 31 kDa and was expressed in the last maturation stages in both skin and pulp tissues. Immunohistochemical analysis showed that it was localised in the first layers of the epidermal tissue, in the vascular bundle cells of the mesocarp, in the placental tissue and in peripheral integuments of the seed. The transport activity of the carrier exhibited higher values for both KM and Vmax, in comparison to the red cultivar, and was inhibited in an uncompetitive manner by quercetin and eriodictyol. These results confirm that BTL homologue acts as a carrier involved in the transport of colourless flavonoids.