GROWTH-CYCLE STAGE-DEPENDENT NACL INDUCTION OF PLASMA-MEMBRANE H-ATPASE MESSENGER-RNA ACCUMULATION IN DE-ADAPTED TOBACCO CELLS()

A cDNA clone encoding an isoform of the plasma membrane H+-ATPase was isolated from Nicotiana tabacum. The steady-state plasma membrane H+-A TPase message levels were the same in unadapted tobacco cells and toba cco cells adapted to 428 mol m(-3) NaCl. When cells adapted to 428 mol m(-3) NaCl maintained in the absence of NaCl (deadapted) for an exces s of 100 passages were exposed to 400 mol m(-3) NaCl for 24 h, there w as an increased accumulation of plasma membrane H+-ATPase message. The NaCl responsiveness of the deadapted cells was dependent upon the gro wth cycle stage. Alterations in the levels of plasma membrane H+-ATPas e message during the growth cycle support a role for the H+-ATPase in cell growth. These results document the induction by NaCl of plasma me mbrane H+-ATPase message accumulation in tobacco cells, and suggest th at enhanced expression of the plasma membrane H+-ATPase has a role in the short term response of cells of NaCl, but is not necessarily invol ved in long-term adaptation.