Fig. 5.

PM H⁺-ATPase activity is reduced in the ssi2 mutant. (A) PM H⁺-ATPase activity was measured in the vesicles of NӦ, ssi2, ProSSI2::SSI2-1, and ProSSI2::SSI2-2 seedlings. Plasma membrane vesicles were isolated from 5-week-old Arabidopsis (ecotype Col-0) seedlings treated with 250 mM NaCl for 3 d. (B) Comparison of PM H⁺-ATPase activity in (A). (C) The net H⁺ effluxes in root tips of NӦ, ssi2, ProSSI2::SSI2-1, and ProSSI2::SSI2-2 seedlings. The non-invasive microsensing system technique was used to monitor ion flux. After the roots were incubated under alkaline conditions (0.5 mM KCl, 0.1 mM CaCl₂, 0.3 mM MES, and 75 mM NaCl, pH 8.1) for 20 min, the transient net H⁺ fluxes were recorded in the same buffer. (D) Calculated net H⁺ effluxes from (C). The data in (B–D) represent means±SD of five replicates. The three biological replicates displayed similar results. Student’s t-test was used to analyse the statistical significance; significant differences (P≤0.05) in (B, D) are indicated by different lower-case letters.