Figure 9.

Influence of the membrane potential on plasma membrane Na⁺/H⁺ exchange in salt-treated Arabidopsis. Plasma membrane vesicles were isolated from the leaves of wild-type plants treated with 250 mm NaCl for 3 d. ΔpH was established as described in the legend to Figure 2 in the absence (A) or presence (B) of the K⁺-ionophore, valinomycin (1 μm). When ΔpH reached steady state, 100 mm NaCl was added to initiate Na⁺/H⁺ exchange activity (dissipation of ΔpH). C, Na⁺/H⁺ exchange was measured over a range of final Na⁺ concentrations (0–100 mm) in the absence (▪) and presence (•) of valinomycin (1 μm) and initial rates of dissipation of ΔpH as a function of Na⁺ concentration are shown. Units of Na⁺/H⁺ exchange are Δ%F mg^-1 protein min^-1. For A and B, one representative experiment of three replicates is shown. Data in C represent means ± se of at least three replicate experiments. Each replicate experiment was performed using independent membrane preparations.