P. aod Lado. P, 1994. Enhanced K*-st!mulated pyropbosphatase activity in NaCl-adapted cells of Acer pseudoplaiatms, Cell suspension cultures of Acer pseudoplatanus L. (Bligny cell line) adapted to growth in the presence of NaCi, are a useful tool for investigating mechanistns for cellular salt tolerance. We eotnpared the activities of vana"date-sensitive {plasma membrane) and nitrate-sensitive (tonoplast) ATPases, and tonoplast K+-stimulated PPase in microsomal fractions (8()0O-108 000 g) from unadapted and NaCi-adapted (80 mtW) cells of A. pseudoplaiatms. Since NaCI reduces the growth rate of the culture, the two cell lines were harvested and compared at both the same cellulai' density and at the same growth phase (middle exponential phase or beginning of the stationary phase). The ATPase activity of the plasma membrane (expressed both on the hasis of protoplast number and in relation to protein contenl) was not affected by the adaptation to salinity. The two enzyme activities of the tonoplast (mainly as expressed on a protein basis) were higher in adapted than in unadapted ceHs. However, a preferential increase in PPase activity took place, although the pH dependeoce, ionic requirements, and apparent Kn, of the PPase activity were the same in the two cell lines. The three enzyme activities showed different sensitivities to detergents such as Triton X-100. Brij 58 and lysophospbatidylcholine (LPC). The stimulation of K*-stimulated PPase activity by detergents was higher in adapted than in unadapted cells. This suggests that the salt-induced enhancement of the PPase activity might partially depend on a modification of the iipid component of the tonoplast.

Cell suspension cultures of Acer pseudoplatanus L. (Bligny cell line) adapted to growth in the presence of NaCl, are a useful tool for investigating mechanisms for cellular salt tolerance. We compared the activities of vanadate‐sensitive (plasma membrane) and nitrate‐sensitive (tonoplast) ATPases, and tonoplast K+‐stimulated PPase in microsomal fractions (8000–108 000 g) from unadapted and NaCl‐adapted (80 mM) cells of A. pseudoplatanus. Since NaCl reduces the growth rate of the culture, the two cell lines were harvested and compared at both the same cellular density and at the same growth phase (middle exponential phase or beginning of the stationary phase). The ATPase activity of the plasma membrane (expressed both on the basis of protoplast number and in relation to protein content) was not affected by the adaptation to salinity. The two enzyme activities of the tonoplast (mainly as expressed on a protein basis) were higher in adapted than in unadapted cells. However, a preferential increase in PPase activity took place, although the pH dependence, ionic requirements, and apparent Km of the PPase activity were the same in the two cell lines. The three enzyme activities showed different sensitivities to detergents such as Triton X‐100, Brij 58 and lysophosphatidylcholine (LPC). The stimulation of K+‐stimulated PPase activity by detergents was higher in adapted than in unadapted cells. This suggests that the salt‐induced enhancement of the PPase activity might partially depend on a modification of the lipid component of the tonoplast.