Figure 4.

ABA and flg22 treatments cannot block light-induced stomatal opening in plants deregulated for HSC70-1 and HSP90 functions. A, Stomatal apertures were measured on epidermal peels incubated 2 h under light and then 2 additional h with or without 100 μm ABA. Average stomatal apertures in presence of ABA were expressed as a percentage of aperture without ABA. B, Average stomatal apertures expressed as percentage of aperture under light without ABA nor radicicol treatment was measured on Col-0 epidermal peels incubated for 2 h in light or darkness with 0 to 100 nm radicicol and 0 to 100 μm ABA. C, Stomatal apertures were measured on epidermal peels incubated in darkness for 2 h and then transferred under light for 2 h with or without 5 μm flg22. Average stomatal apertures in presence of flg22 were expressed as a percentage of aperture without flg22. Three independent measurements (n > 50) were performed per condition on at least three different plants. Experiments were repeated at least twice. Error bar indicate sds. *, Significant differences compared to the wild type (A and C) or the samples without radicicol treatment for each ABA condition (B; Student’s t test, P < 0.001). Chronology of dark (black box)/light (white box) conditions, preparation of peels from plant leaves, treatments with ABA/radicicol/flg22, and measurements of stomatal apertures are indicated above the corresponding experiments. D, Schematic representation of the regulation of stomatal opening/closure by biotic and abiotic factors. Radicicol that inhibits HSP90 ATPase activity acts as a general inhibitor of stomatal closure.