The whole-cell patch-clamp technique was used to study and compare the characteristics of K+-and Na+-transport processes across the plasma membrane in two types of protoplast isolated from NaCl-adapted and -unadapted cells of tobacco (Nicotiana tabacum L. cv. Bright Yellow-2) in suspension culture. In both types of protoplast, with 100 mM KCl in the bathing solution and in the pipette solution, depolarization of the plasma membrane from the holding potential of 0 mV to a positive potential resulted in a relatively large outward current which increased with increasing positive potential, whereas hyperpolarization to negative potentials up to –100 mV resulted in only a small inward current. The outward current activated by depolarization was predominantly carried by K+ ions through K+ channels. Na+ ions also had a finite ability to pass through these K+ channels. The outward K+ and Na+ currents of the NaCl-adapted cells were considerably smaller than those of the NaCl-unadapted cells. These results suggest that adaptation to salinity results in reduced permeability of the plasma membrane to both K+ and Na+ ions.
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Murata et al. (1994) studied this question.