Coordination of plasma membrane and vacuolar membrane ion channels during stomatal movement

Transduction of extracellular signals in guard cells requires coupling of ion fluxes across the vacuolar and plasma membrane. Changes in cytoplasmic proton and Ca2+ concentrations are important messages during stomatal movement. Here we summarize the different biophysical properties of voltage- and ligand-dependent ion channels in both the vacuolar and plasma membranes of guard cells, focusing on how cytoplasmic Ca2+ and proton concentrations direct ion fluxes towards stomatal opening or closure. Particular attention is given to the patch clamp analysis of plasma membrane cation channels (GCKCin, GCKCout and Ca2+ channels), the anion channel (GCAC1) and the vacuolar SV-type channels. A working model is presented of how the ion channels of both membrane systems could communicate to synchronize potassium salt release during stomatal closure.