NaCl responses in tomato calli and whole plants

The comparative salt responses between calli and whole plants were studied in the cultivated tomato species (L. esculentum Mill.) and its wild salt-tolerant relative L. pennellii (Correll) D'Arcy. Based on the reduction in both the callus relative growth rate and plant growth, L. pennellii was more salt-tolerant than L. esculentum, which indicates a positive correlation between the salt responses at both organizational levels. The changes induced by salinity in water contents and osmotic potential (Psi(s)) were different in calli (initiated from leaves) and in leaves of whole plants. In calli, both the water contents and Psi(s) decreased with salinity in the two tomato species, with the reductions being higher in the salt-treated calli of L. esculentum than in those of L. pennellii In contrast to the callus response, the leaf water contents increased with salinity in both species, especially in the wild species. Moreover, a higher Psi(s) reduction as well as a higher solute contribution to the osmotic adjustment were observed in NaCl-treated leaves of L. pennellii than in those of L. esculentum. In both species, the accumulation patterns of Na+ were quite similar in calli and leaves when the contents were calculated on a dry weight basis, with the Na+ accumulation being greater in the wild species. However, the Na+ accumulation was even slightly higher in salt-treated calli of L. esculentum when the contents were calculated on a tissue water basis. The different physiological responses found at both organizational levels were due to the different water uptake capacities of calli and leaves in saline medium; thus, the higher Psi(s) reduction and the higher Na+ accumulation found in the L. esculentum calli were related to the higher callus dehydration by salinity which did not occur in leaves of whole plants. Notwithstanding, the higher K+ levels as well as the higher K+/Na+ selectivity were shown at both organizational levels, although the greatest differences were found at the whole plant level.