Modeling the Calcium Signaling in Stomatal Guard Cells under the Action of Abscisic Acid

A theoretical model of calcium signaling is presented that simulates oscillations of cytoplasmic calcium concentration (Ca²⁺]_cyt) in stomatal guard cells under the action of abscisic acid. The model is based on the kinetics of inositol 1,4,5-trisphosphate-sensitive calcium channels of endoplasmic reticulum and cyclic ADP-ribose-sensitive calcium channels of the tonoplast. The operation of two energy-dependent pumps—the Ca²⁺-ATPase of the endoplasmic reticulum and the Ca²⁺/H⁺ antiporter of the tonoplast—is also included in the model. It is shown that the removal of excessive Ca²⁺ from the cytoplasm by the tonoplast Ca²⁺/H⁺ antiporter is the main factor accounting for generation of Ca²⁺]_cyt oscillations at a wide range of ABA concentrations (0.01–1 M). The long period of Ca²⁺]_cyt oscillations in plant cells is explained by a slow release from inhibition of inositol 1,4,5-trisphosphate-gated calcium channels.