RESUMO
Ultraviolet B (UV-B) radiation induces the activation of MITOGEN-ACTIVATED PROTEIN KINASE PHOSPHATASE1 (MKP1) and its targets MPK3 and MPK6, but whether they participate in UV-B guard cell signaling is not clear. Here, evidence shows that UV-B-induced stomatal closure in Arabidopsis (Arabidopsis thaliana) is antagonistically regulated by MKP1 and MPK6 via modulating hydrogen peroxide (H2O2)-induced nitric oxide (NO) production in guard cells. The mkp1 mutant was hypersensitive to UV-B-induced stomatal closure and NO production in guard cells but not to UV-B-induced H2O2 production, suggesting that MKP1 negatively regulates UV-B-induced stomatal closure via inhibiting NO generation in guard cells. Moreover, MPK3 and MPK6 were activated by UV-B in leaves of the wild type and hyperactivated in the mkp1 mutant, but the UV-B-induced activation of MPK3 and MPK6 was largely inhibited in mutants for ATRBOHD and ATRBOHF but not in mutants for NIA1 and NIA2 mpk6 mutants showed defects of UV-B-induced NO production and stomatal closure but were normal in UV-B-induced H2O2 production, while stomata of mpk3 mutants responded to UV-B just like those of the wild type. The defect of UV-B-induced stomatal closure in mpk6 mutants was rescued by exogenous NO but not by exogenous H2O2 Furthermore, double mutant mkp1/mpk6 and the single mutant mpk6 showed the same responses to UV-B in terms of either stomatal movement or H2O2 and NO production. These data indicate that MPK6, but not MPK3, positively regulates UV-B-induced stomatal closure via acting downstream of H2O2 and upstream of NO, while MKP1 functions negatively in UV-B guard cell signaling via down-regulation of MPK6.
Assuntos
Proteínas de Arabidopsis/metabolismo , Óxido Nítrico/metabolismo , Estômatos de Plantas/fisiologia , Arabidopsis/citologia , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Peróxido de Hidrogênio/metabolismo , Quinases de Proteína Quinase Ativadas por Mitógeno/genética , Quinases de Proteína Quinase Ativadas por Mitógeno/metabolismo , Fosfatases da Proteína Quinase Ativada por Mitógeno/genética , Fosfatases da Proteína Quinase Ativada por Mitógeno/metabolismo , Proteínas Quinases Ativadas por Mitógeno/genética , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Mutação , NADPH Oxidases/genética , NADPH Oxidases/metabolismo , Células Vegetais/metabolismo , Células Vegetais/efeitos da radiação , Estômatos de Plantas/efeitos da radiação , Proteínas Tirosina Fosfatases/genética , Proteínas Tirosina Fosfatases/metabolismo , Transdução de Sinais , Raios UltravioletaRESUMO
Cytosolic alkalization has been shown to function as a key player in multiple stimuli-induced stomatal closure, but its role and relationship with hydrogen peroxide (H2O2) in ultraviolet B (UV-B)-induced stomatal closure remains unknown. In this paper, by stomatal bioassay and laser-scanning confocal microscopy, we observed that 0.5 W m(-2) UV-B induced cytosolic alkalization and H2O2 production in guard cells while inducing stomatal closure in Arabidopsis (Arabidopsis thaliana). Butyrate (a weak acid) reduced the cytosolic pH/H2O2 production and prevented stomatal closure by UV-B. Methylamine (a weak base) induced H2O2 production and stomatal closure while enhancing the cytosolic alkalization in guard cells under light alone. The rise in cytosolic pH of wild-type guard cells on exposure to UV-B was evident at 15 min and substantial at 45 min while H2O2 production started to largely increase after 60 min. The failure of UV-B-induced H2O2 production in AtrbohD/F guard cells did not affect the changes of guard cell pH during the first 60 min of UV-B radiation, but largely suppressed cytosolic alkalization after 60 min of UV-B radiation. These results indicate that cytosolic alkalization mediates UV-B-induced stomatal closure via activating H2O2 production and that H2O2 production can feedback-enhance cytosolic alkalization in Arabidopsis guard cells.
