Fig 5. The system’s response to simulated constitutive activity or external supply of nodes in the absence of abscisic acid (ABA) depends on the initial activity of the protein phosphatases 2C (PP2Cs).

A. The PP2Cs are assumed to be ON in the initial state. The wild-type system in the absence of ABA (open circles) shows lack of closure in all simulations. Constitutively high concentration of cytosolic Ca²⁺ (Ca²⁺_c) or constitutive activity (CA) of Ca²⁺ ATPase similarly leads to lack of closure, but supply of reactive oxygen species (ROS) leads to a response similar to the response to ABA (Fig 3, closed circles). B. The PP2Cs are assumed to be OFF in the initial state. Now there is a nonzero probability of closure in the absence of ABA. Supply of ROS or sustained high Ca²⁺_c leads to a response similar to the response to ABA (Fig 3, closed circles), consistent with experimental observations. CA of the Ca²⁺ ATPase leads to the absence of closure in all simulations. The numerical data can be found in S1 Data.