Isolation of Multiple cDNAs Encoding the Vacuolar H+-ATPase Subunit B from Developing Cotton (Gossypium hirsutum L.) Ovules

Ion Homeostasis in NaCl Stress Environments

“…Suggested by analogy with yeast (discussed below), the prediction is that high external Na+ would trigger, either by excessive Na' influx or reduced K+ uptake, the activation of system 1 and the inhibition of system 2. Consistent with this hypothesis, tobacco cells adapted to NaCl exhibited enhanced capacity for Kt uptake relative to wild-type cells, presumably due to a higher degree of coupling between H+ efflux and K' influx across the plasma membrane (Watad et al, 1991). Further, no inhibition of K+ uptake by NaCl was observed in salt-adapted cells, indicating that these cells had a higher K+/Na' selectivity at the plasma membrane (Watad et al, 1991).…”

“…Consistent with this hypothesis, tobacco cells adapted to NaCl exhibited enhanced capacity for Kt uptake relative to wild-type cells, presumably due to a higher degree of coupling between H+ efflux and K' influx across the plasma membrane (Watad et al, 1991). Further, no inhibition of K+ uptake by NaCl was observed in salt-adapted cells, indicating that these cells had a higher K+/Na' selectivity at the plasma membrane (Watad et al, 1991). Therefore, increased K+/Na+ selectivity of the K+ uptake system might represent a significant adaptation to high concentrations of NaCl.…”

“…Na+ acts as a competitor of K+ uptake (Watad et al, 1991;Schroeder et al, 1994), suggesting that the uptake mechanisms for both cations are similar. Plant roots utilize two systems for Kt acquisition.…”

“…The H+-translocating activities of the plasma membrane ATPase increased in response to NaCl treatment in tobacco cells and roots of the halophyte A. nummularia (Braun et al, 1986;Watad et al, 1991). This up-regulation may be mediated, at least in part, by increased gene expression (Niu et al, 1993a(Niu et al, , 1993bPerezPrat et al, 1994).…”

“…Na'/H+ antiporter) are induced or activated, requiring higher pump activity, whereas after adaptation and when ion gradients have been established across the membrane, altered membrane permeability (eg. reduced passive transport restricting Na+ influx) may be the primary basis for ion homeostasis (Binzel et al, 1988;Watad et al, 1991 Vacuolar compartmentation of Na+ and C1-is an essentia1 mechanism for salt tolerance, since it results in lower cytosolic ion levels and facilitates osmotic adjustment required for cell expansion and maintenance of turgor. Tobacco cells adapted to and growing in 428 mM NaCl accumulated 780 mM Na+ and 624 mM C1-in the vacuole, whereas cytoplasmic levels of both ions were below 100 mM (Binzel et al, 1988).…”