Analysis of cell wall neutral sugar composition, beta-galactosidase activity and a related cDNA clone throughout the development of Vitis vinifera grape berries

Fruit softening during ripening is accompanied by changes in cell wall comp osition due to the action of cell wall modifying enzymes. Moreover, the cel l walls of grape berries form a barrier to the diffusion of aromatic and po lyphenolic compounds which are important for wine quality. Samples of grape berries (Vitis vinifera L., cv Ugni blanc) were harvested in 1996 and 1997 at twelve different developmental stages. The development of berries was c haracterized by physical, chemical and biochemical analysis. Isolated cell walls were analysed for their neutral sugar contents. The main changes duri ng grape berry development were a large decrease in galactose parallel with glucose accumulation, while other neutral sugars (arabinose, rhamnose, xyl ose, fucose and mannose) showed no significant variations. For individual b erries, galactose loss seemed to be softening-related, while galactose remo val per mg of cell wall material was involved in a more general ripening pr ocess. beta-Galactosidase (EC 3.2.1.23) activity was temporally associated with the loss of cell wall-linked galactosyl residues. A 545-base long part ial cDNA (beta-gal10, accession No. AF159124, GenBank) was isolated from fi rst strand cDNA, and shared significant similarities with several beta-gals in data banks. The pattern of transcript expression showed that beta-gal10 was only detectable in the early stages of development, suggesting that be ta-gal10 may encode for a beta-galactosidase active on cell walls during th e early development of grape berries. Relationships between galactose conte nt of the cell wall, beta-galactosidase activity and expression of the corr esponding transcripts, and their possible involvement in grape berry soften ing and ripening are discussed. (C) 2000 Editions scientifiques et medicale s Elsevier SAS.