ABA Receptor Isoforms Differently Regulate Stomatal Movements and Generation of Reactive Oxygen Species in ABA Signaling in Arabidopsis Guard Cells.

Abscisic acid (ABA) signaling in stomatal guard cells is crucial for plants to cope with abiotic stress condition. Pyrabactin is a synthetic agonist of ABA that has a selective affinity to limited isoforms of ABA receptors. Here we investigated the differential utilization of downstream signaling events in guard cell ABA signaling under specific receptor isoforms taking advantage of pyrabactin affinity. Pyrabactin induced stomatal closure as well as ABA, while it did not inhibit stomatal opening. Plasma membrane inwardly rectifying K+ channel was not regulated by pyrabactin, while H+-ATPase activation was negatively regulated by pyrabactin. Pharmacological and molecular genetic evidence supported that reactive oxygen species production occurred differentially between the closure-inducing and opening-inhibiting signals in guard cells. These findings offered a previously unidentified mechanism for ABA signaling events promoting closure induction and opening inhibition of stomata, which were distinct from each other and governed by different ABA receptor isoforms discriminable by their affinity for pyrabactin.