Rapid stomatal closure triggered by a short ozone pulse is followed by reopening to overshooting values.

Stomatal pores, surrounded by the pairs of guard cells, regulate plant gas exchange. Correct stomatal regulation is crucial for plant survival under various stress conditions. We have recently utilized the air pollutant ozone (O3) to study stomatal signaling and showed that application of O3 induces rapid decrease in stomatal conductance. Here we have addressed the recovery of stomatal conductance and show that after exposures of plants to high O3 pulses stomatal conductance recovered faster, reaching higher, “overshooting” values than were the pre-exposure values. We propose the hypothetical mechanism for this phenomenon and discuss it in the frames of current stomatal signaling models.