Comparative alterations in root cell wall constituents and cation-exchange capacity of two tomato cultivars under salinity induced by NaCl and CaCl<sub>2 </sub>

Background: Tomato plants exposed to salinity stress may experience dynamic changes in root growth and cell wall (CW) composition and structure. Aims: Here, we determined the CW composition and cation-exchange capacity (CEC) of two tomato cultivars (Daniela, salt-tolerant and Naomi, salt-sensitive) as well as their growth and root characteristics. Methods: Seedlings of the tomato cultivars were exposed to six NaCl plus CaCl2 concentrations hydroponically, root growth and CW chemical composition were measured. Results: The root growth of Naomi was adversely (P ≤ 0.05) reduced at the elongation zone, but there was little change in the chemical composition of the CW under salinity. A marked reduction occurred in the CW-constituting polysaccharides of Naomi relative to Daniela, whether at the 8.00 dS m-1 NaCl treatment or its combination with CaCl2. For both root zones, CW viscosity was better enhanced under NaCl and CaCl2 combinations, but the contents of uronic acid across the CW constituents increased under sole treatment with CaCl2 at the mature root zone of Naomi. The root CW CEC increased (P ≤ 0.05) with increases in the ionic concentration of the external solution. Salt concentrations at 8.0 dS m-1 NaCl or 8.0 dS m-1 NaCl + CaCl2 increased (P ≤ 0.05) the CEC of the CW, especially for Daniela. Conclusions: The overall results showed that CaCl2 could enhance some tolerance in CW polysaccharides of tomato under salinity stress. The salt-tolerant Daniela with higher CW and ionic contents had superior stability in cell structure under salt stress.