Abstract
This paper aims at analysing the synthesis of flavonoids, their import and export in plant cell compartments, as well as their involvement in the response to stress, with particular reference to grapevine (Vitis vinifera L.). A multidrug and toxic compound extrusion (MATE) as well as ABC transporters have been demonstrated in the tonoplast of grape berry, where they perform a flavonoid transport. The involvement of a glutathione S-transferase (GST) gene has also been inferred. Recently, a putative flavonoid carrier, similar to mammalian bilitranslocase (BTL), has been identified in both grape berry skin and pulp. In skin the pattern of BTL expression increases from véraison to harvest, while in the pulp its expression reaches the maximum at the early ripening stage. Moreover, the presence of BTL in vascular bundles suggests its participation in long distance transport of flavonoids. In addition, the presence of a vesicular trafficking in plants responsible for flavonoid transport is discussed. Finally, the involvement of flavonoids in the response to stress is described.
Highlights
Flavonoids are a group of plant polyphenolic secondary metabolites showing a common three ring chemical structure (C6–C3–C6)
Proanthocyanidins (PAs) synthesis branches off the anthocyanin pathway (LAR, leucoanthocyanidin reductase; ANR, anthocyanidin reductase; STS, stilbene synthase); the black arrows refer to biosynthetic steps missing in grapevine
A direct role of these proteins in vesicular delivery of flavonoids to vacuole and/or cell wall has not yet been demonstrated, a recent study has evidenced an involvement of secretory sensitive factor attachment protein receptors (SNAREs) during extracellular release of callose and antifungal phytochemicals into the apoplast of Arabidopsis cells infected by powdery mildew [80]
Summary
Flavonoids are a group of plant polyphenolic secondary metabolites showing a common three ring chemical structure (C6–C3–C6). The major classes of flavonoids are anthocyanins (red to purple pigments), flavonols (colourless to pale yellow pigments), flavanols (colourless pigments that become brown after oxidation), and proanthocyanidins (PAs) or condensed tannins. These compounds are widely distributed in different amounts, according to the plant species, organ, developmental stage and growth conditions [1]. The monoglycoside forms of anthocyanins are typical end-products of the phenylpropanoid metabolism They may be subjected to further esterification with acetyl or coumaroyl groups, as well as substitution with hydroxyl or methyl groups [4,6], increasing stabilization and colour variation of the pigments. (ii) the translocation and trafficking in grapevine cells, in the frame of the transport mechanisms already described for other plant species; and (iii) their involvement in the response to stress in the grapevine
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