Fluctuations in the protein levels of H+-pumps and water channels of the tonoplast and plasma membrane during grape berry development

Fluctuations of the protein levels of H+-pumps and water channels of tonopl ast and plasma membrane were determined by immunoblot analysis during grape berry development. The growth pattern of a grape berry follows a double si gmoid curve during which many physiological changes are considered to occur , especially after veraison. However, the protein levels of H+-pumps and wa ter channels, except V - ATPase, did not change after veraison. The level o f V - ATPase, one of the tonoplast H+ - pumps, was relatively high at 42 da ys after flowering (DAF) and after veraison. The level of V - PPase, anothe r tonoplast H+-pump, changed more gradually than did that of V-ATPase. Two bands of plasma membrane H+ - pump (P-ATPase) were detected; the level of e ach band changed differently. However, the change in total P-ATPase level w as relatively small during berry development. Changes in the level of water channels of tonoplast and plasma membrane, that is, VM23G and PAQ, respect ively, were similar. That is, their levels, which were lowest at 30 DAF, in creased dramatically at 42 DAF, and thereafter remained nearly constant. In VM23G, the level increased 121 DAF. A previous study in pear fruit suggest ed that a relationship exists between tonoplast water channel and cell expa nsion, but such a relationship did not exist in the grape berry. Both in th e pear fruit and in grape berry, V-ATPase level nearly paralleled that of t he growth rate.