Systems Dynamic Modeling of the Stomatal Guard Cell Predicts Emergent Behaviors in Transport, Signaling, and Volume Control

K⁺ contents and analysis of K⁺ fluxes at the plasma membrane and tonoplast resolved over the diurnal Reference Cycle as described in Figure 1 (12 h light:12 h dark, indicated by bars above). Shown are cytosolic and vacuolar [K⁺] (A), the net K⁺ flux across the plasma membrane and tonoplast (B), the K⁺ flux through the K⁺-permeable transporters at the plasma membrane, comprising the two K⁺ channels and the H⁺-K⁺ symporter (C), and the K⁺ flux through the K⁺-permeable transporters at the tonoplast, comprising the TPK and FV channels (D). K⁺ flux through the TPC channel accounted for less than 1% of either of the other channel fluxes, and has therefore been omitted for purposes of clarity. Note that 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.

Suc and malic acid synthesis, total Mal contents, and analysis of Mal²⁻ fluxes at the plasma membrane and tonoplast resolved over the diurnal Reference Cycle as described in Figure 1 (12 h light:12 h dark, indicated by bars above). Shown are the rates of Suc and Mal synthesis and metabolism (A), total cytosolic and vacuolar [Mal] (B), the net flux of Mal²⁻ across the plasma membrane and tonoplast (C), the Mal²⁻ flux through the Mal²⁻-permeable transporters at the plasma membrane, comprising the SLAC and R- (ALMT-)type anion channels (D), and the Mal²⁻ flux through the Mal²⁻-permeable transporters at the tonoplast, comprising the VMAL and VCL channels (E). Note that 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.

Chloride contents and analysis of Cl⁻ fluxes at the plasma membrane and tonoplast resolved over the diurnal Reference Cycle as described in Figure 1 (12 h light:12 h dark, indicated by bars above). Shown are total cytosolic and vacuolar [Cl⁻] (A), the net flux of Cl⁻ across the plasma membrane and tonoplast (B), the flux of Cl⁻ through the Cl⁻-permeable transporters at the plasma membrane, comprising the SLAC and R- (ALMT-)type anion channels and H⁺-Cl⁻ symporter (C), and the flux of Cl⁻ through the Cl⁻-permeable transporters at the tonoplast, comprising the VCL channel and CLC H⁺-Cl⁻ antiporter (D). Note the difference in scales between C and D. Note that 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.

Cytosolic and vacuolar pH, and analysis of H⁺ fluxes across the plasma membrane and tonoplast resolved over the diurnal Reference Cycle as described in Figure 1 (12 h light:12 h dark, indicated by bars above). Shown are cytosolic and vacuolar pH, pH_c, and pH_v, respectively (A), the net H⁺ flux across the plasma membrane and tonoplast (B), the H⁺ flux through the H⁺-permeable transporters at the plasma membrane, comprising the H⁺-ATPase, and the H⁺-K⁺ and H⁺-Cl⁻ symporters (C), and the H⁺ flux through the H⁺-permeable transporters at the tonoplast, comprising the VH⁺-ATPase, VH⁺-PPase, the CLC H⁺-Cl⁻ antiporter, and the CAX H⁺-Ca²⁺ antiporter (D). Note that 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.

Total cytosolic and vacuolar [Ca²⁺], cytosolic-free [Ca²⁺], and analysis of Ca²⁺ fluxes across the plasma membrane and tonoplast resolved over the diurnal Reference Cycle as described in Figure 1 (12 h light:12 h dark, indicated by bars above). Shown are the total cytosolic and vacuolar [Ca²⁺] (A), [Ca²⁺]_i (B), the net flux of Ca²⁺ across the plasma membrane and tonoplast (C), the Ca²⁺ flux through the Ca²⁺-permeable transporters at the plasma membrane, comprising the hyperpolarization-activated Ca²⁺ channel and the Ca²⁺-ATPase (D), and the flux of Ca²⁺ through the Ca²⁺-permeable transporters at the tonoplast, comprising the Ca²⁺-ATPase, the CAX H⁺-Ca²⁺ antiporter, and the TonVCa Ca²⁺ channel (E). Note the difference in scales between D and E. Note that 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.

[Ca²⁺]_i and analysis of the energetics for Ca²⁺ flux across the plasma membrane and tonoplast resolved over the diurnal Reference Cycle as described in Figure 1 (12 h light:12 h dark, indicated by bars above). Shown in A and F are the current-voltage curves for the dominant Ca²⁺ transporters at the plasma membrane and tonoplast, respectively. Total membrane current is indicated in each case by the dotted line; the free-running membrane voltage is defined by the point at which this line crosses the voltage axis. Also summarized are the plasma membrane and tonoplast voltages (B), the [Ca²⁺]_i (C), and the Ca²⁺ channel and Ca²⁺-ATPase fluxes at the plasma membrane (D) and tonoplast (E). Current-voltage curves are cross-referenced to time points in B to E by letter. Time point b is characterized by plasma membrane hyperpolarization, which favors Ca²⁺ influx through the Ca²⁺ channels at the plasma membrane (A); time point c is characterized by plasma membrane depolarization, which favors Ca²⁺ efflux through the plasma membrane Ca²⁺-ATPase. Note the difference in scales between D and E, which underlines the predominance of Ca²⁺ circulation between the cytosol and the endomembrane store of the vacuole. Note that 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.