NaCl Regulation of Tonoplast ATPase 70-Kilodalton Subunit mRNA in Tobacco Cells

Abstract

osmotica (3, 11, 14). Because cytosolic physiological and biochemical processes apparently are inhibited by high ion concentrations, mechanisms that permit compartmentation of these ions in the vacuole and regulate the concentrations of these ions in the cytosol are of substantial importance for adaptation and growth (11,14,15 for the uphill transport of ions and other solutes into the vacuole. The A/H. across the tonoplast is produced by electrogenic H+ pumps, the H+-ATPase (22), and the H+ translocating pyrophosphatase (17, 25). However, the significance of the pyrophosphatase H+ pump to the generation of the ,AH+ across the tonoplast under physiological conditions is not clear (17,25).H+-ATPases that have been categorized on the basis of similar biochemical properties as V-type enzymes act as H+ pumps in the membranes of a wide variety of acidic compartments in eukaryotes (22). The similarities of the protein sequences of these enzymes have recently been confirmed by analysis of cDNA and genomic clones encoding the major ATPase subunits (12,22). The V-type H+-ATPase is a multimeric enzyme of about 400 to 600 kD that consists of up to nine subunits (22,23). The putative catalytic 70-kD subunit forms a hydrophilic complex with a 60-kD subunit that is the principal component of ATPase activity. The 16-kD proteolipid subunits form a hydrophobic complex that functions in H+ conductance. Additional subunits are postulated to form a stalk connecting these two complexes or to be associated with the proton channel (22).It is reasonable to assume that the V-type H+-ATPase is an enzyme that has to be functional at all times during cell growth. Disruption of the genes encoding the 60-or 70-kD subunits of yeast vacuolar H+-ATPase caused conditional lethality. The mutants grew more slowly than the wild-type cells, failed to grow at neutral pH, and lacked the ability to acidify their vacuoles ( 18,28

Ion Homeostasis in NaCl Stress Environments

“…In barley roots, increased H+ transport activity did not peak until3 d after the onset of NaCl treatment, and this induction was inhibited by protein synthesis inhibitors, indicating that de novo synthesis was required. Accordingly, 70-kD subunit (subunit B) mRNA of the vacuolar H+-ATPase accumulated in response to NaCl treatment (Narasimhan et al, 1991). These data imply that salt-induced H+ transport activity of the tonoplast ATPase is mediated through increased gene expression.…”

Salt regulation of transcript levels for the c subunit of a leaf vacuolar H+‐ATPase in the halophyte Mesembryanthemum crystallinum

“…A higher specific activity of the V-ATPase was observed in saltadapted compared with unadapted suspension-culture cells of Nicotiana tabacurn (Reuveni et aL, 1990), and was found to be associated with a small growth-phasedependent increase in mRNA levels for the A subunit (Narasimhan et aL, 1991). HSrtensteiner et aL (1994) also detected a slight increase in transcript levels for the B subunit of the V-ATPase caused by salt during growth of evacuolated protoplasts of N. tabacum, but this was concluded to reflect an osmotic effect on the rate of vacuole regeneration.…”

Identification of salt-induced genes from Salicornia brachiata, an extreme halophyte through expressed sequence tags analysis

“…It has been reported that salt treatment of plants induces the activities of the plasma membrane and tonoplast proton pumps (Reuveni et al, 1990;Niu et al, 1993;Perez-Prat et al, 1994;Binzel, 1995;Klobus and Janicka-Russak, 2004). Accumulation of both PM-H + ATPase (Niu et al, 1993;Perez-Prat et al, 1994) and V-H + ATPase (Narasimhan et al, 1991) mRNAs under NaCl-stress and the positive correlation with salt tolerance (Braun et al, 1986;Niu et al, 1993;Perez-Prat et al, 1994) are well studied. In the halophyte Atriplex nummularia Lindl., the proton transport capacity of the PM-H + ATPase has been reported by higher Na + concentration (Niu et al, 1993).…”