Dynamics of homeostats: the basis of electrical, chemical, hydraulic, pH and calcium signaling in plants.

Homeostats are important to control homeostatic conditions. Here, we have analyzed the theoretical basis of their dynamic properties by bringing the K homeostat out of steady state (i) by an electrical stimulus, (ii) by an external imbalance in the K⁺ or H⁺ gradient or (iii) by a readjustment of transporter activities. The reactions to such changes can be divided into (i) a short-term response (tens of milliseconds), where the membrane voltage changed along with the concentrations of ions that are not very abundant in the cytosol (H⁺ and Ca²⁺), and (ii) a long-term response (minutes and longer) caused by the slow changes in K⁺ concentrations. The mechanistic insights into its dynamics are not limited to the K homeostat but can be generalized, providing a new perspective on electrical, chemical, hydraulic, pH and Ca²⁺ signaling in plants. The results presented here also provide a theoretical background for optogenetic experiments in plants.