Changes in cell-wall polysaccharides from the mesocarp of grape berries during veraison

Softening of grape berries (Vitis vinifera L, x V, labrusca L, cv, Kyoho) w as evaluated by studying changes in composition and degradation of cell-wal l polysaccharides, The grape berry softens at the beginning of the second g rowth cycle many weeks before harvest. The softening stage is called 'verai son' by viticulturists. On day 50 after full bloom, green hard berries (bef ore veraison [BV]), softening berries (veraison [V]) and partly peel colore d berries (C) were selected from the same clusters. In addition, mature ber ries (M) were collected on day 78 after full bloom. Mesocarp tissues at eac h stage were fractionated into hot water-soluble (WS), hot EDTA-soluble (pe ctin), alkali-soluble (hemicellulose) and residual (cellulose) fractions. N eutral and acidic sugar contents of WS and pectin fractions decreased only after the V stage, while the neutral sugar content of the hemicellulose fra ction decreased from the BV to V stages, Cellulose content constantly decre ased as the berry ripened, but the large decrease was found from the BV to V stages. Molecular masses of pectic and hemicellulosic polysaccharides dec reased from the BV to V stages. Hemicellulosic xyloglucan was markedly depo lymerized from the BV to V stages. The neutral and acidic sugar composition of each fraction changed little during the berry ripening. These data indi cated that softening of berry during veraison involved the depolymerization of pectin and xyloglucan molecules and decrease in the amounts of hemicell ulose and cellulose.