Figure 4.

Na⁺ impairs the K⁺ permeability of the plasma membrane of sos1 root cells but not the wild type. A, K⁺ permeability of the plasma membrane of root cells measured as K⁺-induced shifts in V_m in seedlings pretreated for 10 h with 50 mm NaCl. The K⁺ permeability of sos1 root cells measured by shifting [K⁺] from 10 to 100 μm was severely impaired by the Na⁺ pretreatment, while other genotypes were not. The response to shifts from 100 to 1,000 μm was also less in sos1 plants relative to wild type (P = 0.01). This effect of Na⁺ on K⁺ permeability can explain the growth rate results in Figure 3. The values shown for each genotype are means ± se of at least five independent measurements on separate seedlings. B, Example recordings of V_m showing wild-type and sos1 individual responses to 10-fold shifts in [K⁺] of the bathing medium.