Fluctuations in the Protein Levels of H⁺-pumps and Water Channels of the Tonoplast and Plasma Membrane during Grape Berry Development

Abstract

Fluctuations of the protein levels of H⁺-pumps and water channels of tonoplast and plasma membrane were determined by immunoblot analysis during grape berry development. The growth pattern of a grape berry follows a double sigmoid curve during which many physiological changes are considered to occur, especially after veraison. However, the protein levels of H⁺-pumps and water channels, except V-ATPase, did not change after veraison. The level of V-ATPase, one of the tonoplast H⁺-pumps, was relatively high at 42 days after flowering (DAF) and after veraison. The level of V-PPase, another 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 each band changed differently. However, the change in total P-ATPase level was relatively small during berry development. Changes in the level of water channels of tonoplast and plasma membrane, that is, VM23G and PAQ, respectively, were similar. That is, their levels, which were lowest at 30 DAF, increased dramatically at 42 DAF, and thereafter remained nearly constant. In VM23G, the level increased 121 DAF. A previous study in pear fruit suggested that a relationship exists between tonoplast water channel and cell expansion, but such a relationship did not exist in the grape berry. Both in the pear fruit and in grape berry, V-ATPase level nearly paralleled that of the growth rate.