Catalases negatively regulate methyl jasmonate signaling in guard cells.

Methyl jasmonate (MeJA)-induced stomatal closure is accompanied by the accumulation of hydrogen peroxide (H₂O₂) in guard cells. In this study, we investigated the roles of catalases (CATs) in MeJA-induced stomatal closure using cat mutants cat2, cat3-1 and cat1 cat3, and the CAT inhibitor, 3-aminotriazole (AT). When assessed with 2',7'-dichlorodihydrofluorescein, the reduction of catalase activity by means of mutations and the inhibitor accumulated higher basal levels of H₂O₂ in guard cells whereas they did not affect stomatal aperture in the absence of MeJA. In contrast, the cat mutations and the treatment with AT potentiated MeJA-induced stomatal closure and MeJA-induced H₂O₂ production. These results indicate that CATs negatively regulate H₂O₂ accumulation in guard cells and suggest that inducible H₂O₂ production rather than constitutive elevation modulates stomatal apertures in Arabidopsis.