Plant salinity tolerance is a polygenic trait with contributions from genetic, developmental, and physiological interactions, in

addition to interactions between the plant and its environment. In this study, we show that in salt-tolerant genotypes of barley

(Hordeum vulgare), multiple mechanisms are well combined to withstand saline conditions. These mechanisms include: (1)

better control of membrane voltage so retaining a more negative membrane potential; (2) intrinsically higher H1 pump activity;

(3) better ability of root cells to pump Na1 from the cytosol to the external medium; and (4) higher sensitivity to supplemental

Ca21. At the same time, no significant difference was found between contrasting cultivars in their unidirectional 22Na1 influx or in

the density and voltage dependence of depolarization-activated outward-rectifying K1 channels. Overall, our results are consistent

with the idea of the cytosolic K1-to-Na1 ratio being a key determinant of plant salinity tolerance, and suggest multiple

pathways of controlling that important feature in salt-tolerant plants.