Interactions between salinity and boron toxicity in tomato plants involve apoplastic calcium

The lack of consensus about the mutual relations between salinity and boron (B) toxicity with respect to the physiological response of plants necessitates investigation of the interactions of soluble B with salinity. In this investigation, the effect of B was compared with Ca in order to elucidate whether the two nutrients have similar effects and/or to elucidate a relationship under salinity. Following addition of B or Ca, salinity was applied to tomato plants and the cell wall and plasma membrane permeability, measured as water permeability and electrolyte leakage, in relation to amino acid and ion cell wall composition, were determined. As the relationship between B and salinity was complex, several hypotheses are established. The increase of aquaporin functionality due to the presence of B and Ca compared with NaCl-treated plants could be the most feasible, whereas there is currently no satisfactory explanation for the results for the cell wall amino acid composition. In addition, the elemental composition results revealed that, in addition the known interactions between B and Ca with respect to cell wall stability, Mg and Mn were also increased in NaCl+B and NaCl+Ca treatments, suggesting their possible involvement in the cell wall function necessary for plant growth.