In the bright fields, stomata of the plants are fully opened to raise the transpiration rate and CO2 uptake required for photosynthesis. Stomatal opening is driven by the activation of plasma membrane H+-ATPase and K-in(+) channels, and the Ca2+-dependent inactivation and blockage of both components were supposed to be inevitable function to regulate the stomatal aperture. Although, it is still obscure how these activities are regulated at the open state. Application of an amphipathic membrane creator, trinitrophenol (TNP), instantly generates the convex curvature in the plasma membrane, which occurs in the phases of stomatal opening and closure. TNP surely activates mechanosensitive Ca2+-permeable channels and attenuates the promotion of stomatal opening, but does not inhibit and promote stomatal closure. These results suggest that activation of mechanosensitive Ca2+-permeable channels regulates the opening phase of stomata in plants. (c) 2007 Elsevier Inc. All rights reserved.