Elevated CO2 (800 ppm) activates S-type anion currents in WT, ABA biosynthesis mutant, and ABA receptor mutant guard cell protoplasts. (A) Whole-cell recordings of S-type anion currents at the indicated CO2 concentrations in the bath solution in WT, nced3/nced5 double mutant (nced3/5), and pyr1/pyl1/pyl2/pyl4/pyl5/pyl8 (rcar3/8/10/11/12/14) hextuple mutant (pyr1/pyl1/2/4/5/8) guard cells. (B) Average current–voltage curves of guard cell S-type anion channel currents recorded in WT, nced3/5, and pyr1/pyl1/2/4/5/8. Data represent mean ± SEM.