TISSUE-SPECIFIC EXPRESSION OF THE GENE FOR A PUTATIVE PLASMA-MEMBRANEH-ATPASE IN A SEAGRASS()

A cDNA clone corresponding to the gene (ZHA1) for a putative plasma me mbrane H+-ATPase of a seagrass (Zostera marina L.) was isolated and se quenced. Comparison of the amino acid predicted sequence from the nucl eotide sequence of ZHA1 with those encoded by known genes for plasma m embrane H+-ATPases from other plants indicated that ZHA1 is most simil ar to the gene (PMA4) for a plasma membrane H+-ATPase in a tobacco (84 .4%). Northern hybridization indicated that ZHA1 was strongly expresse d in mature leaves, which are exposed to seawater and have the ability of tolerate salinity; ZHA1 was weakly expressed in immature leaves, w hich are protected from seawater by tightly enveloping sheaths and are sensitive to salinity. In mature leaves, in situ hybridization reveal ed that ZHA1 was expressed specifically in epidermal cells, the plasma membranes of which were highly invaginated and morphologically simila r to those of typical transfer cells. Therefore, the differentiation o f the transfer cell-like structures, accompanied by the high-level exp ression of ZHA1, in the epidermal cells of mature leaves in particular may be important for the excretion of salt by these cells.