NACL REGULATION OF PLASMA-MEMBRANE H-ATPASE GENE-EXPRESSION IN A GLYCOPHYTE AND A HALOPHYTE()

NaCl regulation of plasma membrane H+-ATPase gene expression in the gl ycophyte tobacco (Nicotiana tabacum L. var Wisconsin 38) and the halop hyte Atriplex nummularia L. was evaluated by comparison of organ-speci fic mRNA abundance using homologous cDNA probes encoding the ATPases o f the respective plants. Accumulation of mRNA was induced by NaCl in f ully expanded leaves and in roots but not in expanding leaves or stems . The NaCl responsiveness of the halophyte to accumulate plasma membra ne H+-ATPase mRNA in roots was substantially greater than that of the glycophyte. Salt-induced transcript accumulation in A. nummularia root s was localized by in situ hybridization predominantly to the elongati on zone, but mRNA levels also increased in the zone of differentiation . Increased message accumulation in A. nummularia roots could be detec ted within 8 h after NaCl (400 mM) treatment, and maximal levels were severalfold greater than in roots of untreated control plants. NaCl-in duced plasma membrane H+-ATPase gene expression in expanded leaves and roots presumably indicates that these organs require increased H+-ele ctrochemical potential gradients for the maintenance of plant ion home ostasis for salt adaptation. The greater capacity of the halophyte to induce plasma membrane H+-ATPase gene expression in response to NaCl m ay be a salt-tolerance determinant.