The plastids of the grape pericarp and their significance in isoprenoid synthesis

Plastids were found to be present in the pericarp of berries of Vitis vinifera cv. Traminer throughout their development, but their morphology changed. They progressed from a small amyloplast stage at anthesis to take on a larger pleomorphic form thereafter. The latter form was largely devoid of starch granules until the last stages of ripening but contained large lipid like globules. At each developmental stage, the ultrastructural morphology of the plastids contained in pericarp cells was similar. Concurrent and parallel changes within the pericarp in the amounts of lipid like globules and monoterpenes may indicate that presence of the former is biosynthetically associated with the latter. Isoprenoid secondary metabolites such as monoterpenes and damascenone are important contributors to grape and wine flavour and aroma. From this and other studies one may conclude that the plastids within the grape pericarp play a central role in the development of these constituents, and thus in that of grape flavour. An understanding of their biosynthetic regulation will require further knowledge of the biochemistry of grape isoprenoid synthesis, the molecular biology of the plastids and the interaction of the genomes of the nuclei and plastids.