MAP kinase specifically mediates the ABA-induced H2O2 generation in guard cells ofVicia faba L.

Abstract

Mitogen-activated protein (MAP) kinase is involved in ABA-or H2O2-signaling, and H2O2 acts as intermediate in the downstream of ABA signal transduction pathway, which has recently emerged as a secondary messenger of ABA signaling. Using an epidermal strip bioassay and laser scanning confocal microscope, we provided the first evidence that MAP kinase plays an important role in H2O2 signal initial, amplification and specific targeting in response to stimuli in guard cells. ABA-or H2O2-inducedVicia faba stomatal closure was inhibited or reversed by the specific inhibitor PD98059 of MEK1/2; the guard cells were pre-incubated or -microinjected by 10 μmol · L−1 PD98059, ABA could not enhance the fluorescence intensity of H2O2 probe dichlorofluorescein (DCF). Meanwhile, after ABA induced the H2O2 accumulation in guard cells, the exogenous or intracellular PD98059 could reduce the DCF fluorescence intensity. Most interestingly, on the contrary to ABA, the DCF fluorescence intensity of guard cells treated by 100 μmol · L−1 salicylic acid (SA) was not down-regulated by PD98059, yet PD98059 did not regulate the stomatal movement being induced by light, dark or salicylic acid. These results suggest that MEK1/2 could mediate stomatal closure by abolishing the ABA-induced H2O2 generation/accumulation in the specific manner.