FIGURE 11-29 Concentration of ions and sucrose by the plant vacuole. The vacuolar membrane contains two types of proton pumps (orange): a V-class H⁺ ATPase (left) and a pyrophosphate-hydrolyzing proton pump (right) that differs from all other ion pumps and is probably unique to plants. These pumps generate a low luminal pH as well as an inside-positive electric potential across the vacuolar membrane by their inward pumping of H⁺ ions. The inside-positive potential powers the movement of Cl⁻ and NO₃⁻ from the cytosol through separate channel proteins (purple). Proton antiporters (green), powered by the H⁺ gradient, accumulate Na⁺, Ca²⁺, and sucrose inside the vacuole. See B. J. Barkla and O. Pantoja, 1996, Annu. Rev. Plant Phys. 47:159–184 and P. A. Rea et al., 1992, Trends Biochem. Sci. 17:348.