Roles of intracellular hydrogen peroxide accumulation in abscisic acid signaling in Arabidopsis guard cells

Reactive oxygen species (ROS), including hydrogen peroxide (H2O2), are among the important second messengers in abscisic acid (ABA) signaling in guard cells. In this study, to investigate specific roles of H2O2 in ABA signaling in guard cells, we examined the effects of mutations in the guard cell-expressed catalase (CAT) genes, CAT1 and CAT3, and of the CAT inhibitor 3-aminotriazole (AT) on stomatal movement. The cat3 and cat1 cat3 mutations significantly reduced CAT activities, leading to higher basal level of H2O2 in guard cells, when assessed by 2′,7′-dichlorodihydrofluorescein, whereas they did not affect stomatal aperture size under non-stressed condition. In addition, AT-treatment at concentrations that abolish CAT activities, showed trivial affect on stomatal aperture size, while basal H2O2 level increased extensively. In contrast, cat mutations and AT-treatment potentiated ABA-induced stomatal closure. Inducible ROS production triggered by ABA was observed in these mutants and wild type as well as in AT-treated guard cells. These results suggest that ABA-inducible cytosolic H2O2 elevation functions in ABA-induced stomatal closure, while constitutive increase of H2O2 do not cause stomatal closure.