Comparative NaCl tolerance of lucerne plants regenerated from salt-selected suspension cultures

Batch suspension cultures of Lucerne (Medicago media cv. Rambler), initiated directly from surface-sterilized leaflet explants, were used to produce cell lines tolerant to 200, 250 and 300 mol/m(3) NaCl by successive subculture into media of progressively higher salinity. Plants regenerated from these cell lines were significantly more salt tolerant than the original, unselected Rambler plants, another cultivar of M. media and 4 cultivars of M. sativa. The salt-tolerant plants showed enhanced Na+ and Cl- exclusion when compared with the unselected cultivars. Comparisons of the salt-tolerant, 250 mol/m(3) NaCl-selected with original unselected Rambler plants showed the salt-tolerant plants were able to maintain lower Na+/K+ ratios than the unselected plants. Ca2+ gave some amelioration of NaCl toxicity but the salt-tolerant plants did not differ from the susceptible plants in this respect. A multiple regression equation has been computed accounting for 90% of the observed variation, that relates the growth of the plants to Na+/K+ ratios and Cl- concentrations of roots and shoots and their interactions.