Abscisic Acid signaling simulations: a) Effect of mutations on closure in asynchronous Boolean simulation of ABA induced closure. Blue line indicates the closure response (percentage of simulations with Closure = 1) in wild type (WT). Three other knockout mutants: S1P (green line), PA (red line) and pHc (light-blue line) were shown experimentally to be less sensitive to ABA in term of ABA-induced stomatal closure. b) Variability of closure in WT, pHc knockout and PA knockouts in a piece-wise linear simulation. The mean of the continuous variable corresponding to the node Closure in 300 simulations is plotted as a solid line and dashed lines indicate the mean plus or minus standard deviation. In the WT simulation the variation of closure (blue lines) is small during the first 20 time steps, increases from 20 to 50 time steps and gradually decreases to 0 after 50 time steps. In PA (red lines) and pHc (light blue lines) knockout mutants, although the mean closure responses are similar to that of WT, the variances are not decreasing after 50 time steps.