Role and interrelationship of MEK1-MPK6 cascade, hydrogen peroxide and nitric oxide in darkness-induced stomatal closure

Abstract Pharmacological data have suggested the involvement of mitogen-activated protein kinase (MPK) cascades in dark-induced stomatal closure, but which specific MPK cascade participates in the darkness guard cell signaling and its relationship with hydrogen peroxide (H 2 O 2 ) and nitric oxide (NO) remain unclear. In this paper, we observed that darkness induced activation of MPK6 in leaves of wild-type Arabidopsis ( Arabidopsis thaliana ) and mutants for nitrate reductase 1 ( NIA1 ), but this effect was inhibited in mutants for MPK Kinase 1 (MEK1) and ATRBOHD/F . Mutants for MEK1 , MPK6 and NIA1 showed defect of dark-induced NO production in guard cells and stomatal closure, but were normal in the dark-induced H 2 O 2 generation, while stomata of mutant AtrbohD/F showed defect of dark-induced H 2 O 2 and NO production and subsequent closure. Moreover, exogenous NO rescued the defect of dark-induced stomatal closure in mutants of AtrbohD/F , mek1 and mpk6 , while exogenous H 2 O 2 could not rescue the defect of dark-induced stomatal closure in mutants of mek1 , mpk6 and nia1 . These genetic and biochemical evidences not only show that MEK1-MPK6 cascade, AtRBOHD/F-dependent H 2 O 2 and NIA1-dependent NO are all involved in dark-induced stomatal closure in Arabidopsis, also indicate that MEK1-MPK6 cascade functions via working downstream of H 2 O 2 and upstream of NO.