Identification of the membrane transport proteins that allow Na+ entry into plant cells under salinity stress remains an outstanding problem. One candidate is a non-selective channel that can transport cations, the molecular identity of which remains elusive. Could this elusive mechanism be mediated by an aquaporin? Aquaporins impart selective membrane permeability to water which is essential for all life, and a subset of animal aquaporins function as dual ion and water channels but to date this function has not been reported for plant aquaporins. We observed ionic conductance for a subset of plant plasma membrane intrinsic protein (PIP) aquaporins when expressed in heterologous systems. One of these PIPs is highly abundant in root epidermal cell plasma membranes. The non-selective cation channel that allows toxic entry of Na+ into plant roots in saline conditions is inhibited by Ca2+, as is the ionic conductance of this PIP of interest. The observation that Na+ can permeate this PIP could explain a long-standing mystery in plant biology regarding the molecular basis for Na+ fluxes during salt stress.