Long-term culture modifies the salt responses of callus lines of salt-tolerant and salt-sensitive tomato species

The changes in the salt responses induced by long term callus culture were studied in leaf callus tissues of the cultivated tomato species (Lycopersic on esculentum Mill.) and its wild salt-tolerant relative L. penneliii (Corr ell) D'Arcy. The salt-tolerant wild species was able to adapt very quickly to the salt medium: after only three subcultures in salt medium (175 mmol/L NaCl) the callus relative growth rate (RGR) and the cell volume were highe r in the salt medium than in the control. In the cultivated species, two ph ases or steps were distinguished. In the first, callus RGR and cell volume tended to decrease with the subculture, both in the control and in the sali ne media (100 mmol/L NaCl), although the growth reduction was higher in str essful medium; this step seems to correspond to an adaptive period. In the second step, which would correspond to the phase following the adaptive per iod, callus RGR and cell volume increased as subculture advanced. In both s pecies, the different growth changes along the subcultures had an influence on the degree of salt tolerance. Furthermore, the salt responses varied ac cording to the precedence of calli (from control or saline media). In any c ase, the salt tolerance of the wild species was much higher than that of th e cultivated species. The possibilities of using tissue cultures as tools t o obtain salt-tolerant lines, as well as to evaluate the salt tolerance, ar e discussed.