Fig. 4.

Chloride contents and analysis of Cl⁻ fluxes at the plasma membrane and tonoplast. Outputs resolved over a standard diurnal cycle (12 h light:12 h dark, indicated by bars above) (Chen et al., 2012) for the wild-type (left) and the ost2 mutant (right). Shown are (A) total cytosolic and vacuolar [Cl⁻], (B) the net flux of Cl⁻ across the plasma membrane and tonoplast, and (C) the flux of Cl⁻ through the Cl⁻-permeable transporters at the plasma membrane (SLAC and R- (ALMT-) type anion channels and H⁺–Cl⁻ symporter). Again, positive flux is defined as movement of the ionic species (not the charge) out of the cytosol, either across the plasma membrane or the tonoplast. Note the elevation in [Cl⁻] in both the cytosol and vacuole, and the loss in their dynamics in the ost2 mutant. Closure was marked by a large flux of Cl⁻ from the vacuole to the cytosol and export across the plasma membrane, but the pattern was lost in the mutant, reflecting the loss of cyclic changes in voltage and [Ca²⁺]_i that drive solute efflux from the vacuole and across the plasma membrane [see Chen et al. (2012)].