Abstract
An NaCl-resistant line has been developed from suspension-cultured tobacco cells (Nicotiana tabacum/gossii) by stepwise increases in the NaCl concentration in the medium. Resistance showed stability through at least 24 generations in the absence of added NaCl.
Above an external NaCl concentration of 35 millimolar, proline concentration in the selected cells rose steeply with external NaCl, particularly so above 100 millimolar NaCl. Proline accumulation in the wild type was far slighter. Selected cells which had been grown for 24 generations in the absence of added NaCl accumulated proline strongly on re-exposure to NaCl medium, indicating stability of this character. Proline accumulation was fully reversible with a half-time of about 6 hours. When selected cells were transferred sequentially to lower and lower NaCl concentrations, their proline content fell to the level corresponding to the new NaCl concentration. The NaCl-selected cells responded to water stress (i.e. added mannitol) by accumulating markedly more proline than did the wild type.
The addition of Ca2+ to the growing and rinsing media minimized Na+ and K+ binding in the Donnan free space of cell walls and thus allowed assessment of intracellular Na+ and K+. In both cell types, internal Na+ content rose steadily as a function of external NaCl concentration. In the course of 7 days in NaCl media, the wild type cells lost a considerable part of their K+ content, the extent of the loss increasing with rise in external NaCl concentration. The selected cells, by contrast, lost no K+ at external NaCl concentrations below 50 millimolar external NaCl, and at higher concentrations lost less than the wild type.
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