Figure 5.

Constitutively active recombinant SOS2 protein stimulates plasma membrane Na⁺/H⁺-exchange activity in vesicles isolated from wild-type, sos2, and sos3 plants but not in those isolated from sos1 plants. Transport assays were performed as described in Materials and Methods. ΔpH was formed in the absence (●) or presence (○) of active recombinant SOS2 protein (GST-T/DSOS2DF). When ΔpH reached steady state, NaCl was added over a range of final concentrations (0–100 mM), and the initial rates of dissipation were measured. (A) Wild-type. (B) sos1. (C) sos2. (D) sos3. The units of Na⁺/H⁺-exchange activity are Δ%F/min per mg of protein.