Figure 1.

Schematic drawing of a simplified plant cell model representing Na⁺ transport proteins discussed in this review. Regions surrounded by dotted lines indicate hypotheses and subjects that remain to be shown. Plasma membrane Na⁺/H⁺ antiporter SOS1 and Na⁺ transporter AtHKT1 have been hypothesized to transport in either direction depending on conditions (Shi et al., 2002; Berthomieu et al., 2003). Vacuolar Na⁺/H⁺ antiporter AtNHX1 is hypothesized to transport K⁺ (Zhang and Blumwald, 2001; Venema et al., 2002) and Li⁺ (Qiu et al., 2004) in addition to Na⁺.