The SOS signaling pathway has emerged as a key mechanism in preserving the homeostasis of Na⁺ and K⁺ under saline conditions. We have recently identified and functionally characterized, by complementation studies in yeast, the gene encoding the durum wheat plasma membrane Na⁺/H⁺ antiporter (TdSOS1). To extend these functional studies to the whole plant level, we complemented Arabidopsis sos1-1 mutant with wild-type TdSOS1 or with the hyperactive form TdSOS1∆972 and compared them to the Arabidopsis AtSOS1 protein. The Arabidopsis sos1-1 mutant is hypersensitive to both Na⁺ and Li⁺ ions. Compared with sos1-1 mutant transformed with the empty binary vector, seeds from TdSOS1 or TdSOS1∆972 transgenic plants had better germination under salt stress and more robust seedling growth in agar plates as well as in nutritive solution containing Na⁺ or Li⁺ salts. The root elongation of TdSOS1∆972 transgenic lines was higher than that of Arabidopsis sos1-1 mutant transformed with TdSOS1 or with the endogenous AtSOS1 gene. Under salt stress, TdSOS1∆972 transgenic lines showed greater water retention capacity and retained low Na⁺ and high K⁺ in their shoots and roots. Our data showed that the hyperactive form TdSOS1∆972 conferred a significant ionic stress tolerance to Arabidopsis plants and suggest that selection of hyperactive alleles of the SOS1 transport protein may pave the way for obtaining salt-tolerant crops.