Fig. 3.

Ca²⁺-sensitivity priming. In the Ca²⁺-sensitivity priming model, the response of a cell to a given stimulus depends on the conditions the cell has previously experienced. A generic model is presented, where the magnitude of Ca²⁺ increases and ABA-dependent priming combine to determine the eventual response (Siegel et al., 2009; Chen et al., 2010). Without a specific stimulus only spontaneous [Ca²⁺]_cyt transients occur. In the presence of a stimulus (X) the amplitude of transients increases, but in the un-primed state this is insufficient to trigger the downstream response (e.g. ion-channel activation). A previously encountered condition (e.g. ABA) may modulate a Ca²⁺-response pathway, making it more Ca²⁺ responsive or ‘primed’. When stimulus X is perceived under the primed conditions the sensor is more Ca²⁺ responsive and therefore downstream responses are triggered. Note, however, that [Ca²⁺]_cyt sensitivity enhancement could theoretically occur at any point in the network downstream of or parallel to [Ca²⁺]_cyt. See text for details.