Early post-veraison growth in grapes: evidence for a two-step mode of berry enlargement

An account is provided of berry softening plus cell wall loosening in flesh and skin tissues, that relates to changes in berry turgor and sugar accumu lation around veraison in Golden Muscat (Vitis vinifera x V. labrusca). The onset of change in berry deformability was taken as a demarcation between pre-veraison and post-veraison growth phases. Our results confirmed that po st-veraison berry enlargement was preceded by berry softening and sugar acc umulation. Berry 'turgor' (as inferred from the rate of juice exudation fro m punctured fruit) increased abruptly and concurrently with berry softening and sugar accumulation, but dropped steadily with subsequent berry expansi on. Elasticity of skin tissues decreased abruptly during early phases of ex pansion, while berry deformability increased. We suggest that cell wall loo sening in flesh tissues precedes cell wall loosening in skin tissues, and t hat this loosening sequence results in a two step sequence where berry soft ening is later followed by berry expansion.