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 (Lycopersicon esculentum Mill.) and its wild salt-tolerant relative L. penneliii (Correll) 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 higher in the salt medium than in the control. In the cultivated species, two phases 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 saline media (100 mmol/L NaCl), although the growth reduction was higher in stressful medium; this step seems to correspond to an adaptive period. In the second step, which would correspond to the phase following the adaptive period, callus RGR and cell volume increased as subculture advanced. In both species, the different growth changes along the subcultures had an influence on the degree of salt tolerance. Furthermore, the salt responses varied according to the precedence of calli (from control or saline media). In any case, the salt tolerance of the wild species was much higher than that of the cultivated species. The possibilities of using tissue cultures as tools to obtain salt-tolerant lines, as well as to evaluate the salt tolerance, are discussed.