Enhanced K⁺‐stimulated pyrophosphatase activity in NaCl‐adapted cells of Acer pseudoplatanus

Abstract

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.

High V‐PPase activity is beneficial under high salt loads, but detrimental without salinity

“…With respect to the V-ATPase, the hydrolytic activity is often enhanced in response to saline treatments (Nakamura et al, 1992;Wang et al, 2001;Kabała & Kłobus, 2008;Queir os et al, 2009). However, as Wang et al (2001) andQueir os et al (2009) outlined, no common pattern in the regulation of the V-PPase activity under salinity has been obtained; examples for V-PPase from different plant species have been reported as inhibited, insensitive and activated by salt treatments (Nakamura et al, 1992;Colombo & Cerana, 1993;Zingarelli et al, 1994;Wang et al, 2001;Kabała & Kłobus, 2008;Krebs et al, 2010). What could be the reason for these apparent differences?…”