Growth, ion content and proline accumulation in NaCl-selected and non-selected cell lines of lucerne cultured on sodium and potassium salts

Batch suspension cultures of Lucerne (Medicago media cv Rambler), established directly from surface-sterilized leaflet explants, were subcultured into media of progressively higher salinity to produce a cell line tolerant to 400 mol/m(3) NaCl. After these cells were grown for eight passages (28 days each) on NaCl-free medium, the cells were still more salt-tolerant than non-selected cells when recultured to salt supplemented media. The exposure of the NaCl-tolerant cell line to equimolar concentrations of salts other than NaCl resulted in enhanced tolerance to Na2SO4 or K2SO4 but limited tolerance to KCl. The salt-tolerant cell line showed enhanced Na+ exclusion and was able to maintain higher K+ and much lower Na+/K+ ratios than the non-selected cell line in response to NaCl or Na2SO4 stress. The proline concentration was much higher in the salt-selected compared with the non-selected cell line under NaCl or Na2SO4 stress. Proline accumulation did not result from K2SO4 or KCl stress in either selected or non-selected cell lines, suggesting this is a response to Na+ rather than Cl- or K+. The results suggest that growth inhibition in selected and non-selected cells under KCl stress could result from the toxic effects of Cl-. (C) 1997 Elsevier Science Ireland ltd.