Abstract
Stomata open in response to blue light. Blue light is absorbed by phototropin as a receptor and activates the plasma membrane H+ pump in stomatal guard cells. The activated pump creates a driving force to uptake K+ through the inward-rectifying K+ channels. However, entire signaling components for the stomatal opening are largely unknown. In order to identify the components, we screened and isolated Arabidopsis mutants impairing light-induced stomatal opening using infrared thermography. In this study, we characterized a mutant named as 24-H9 that indicated the high leaf temperature under the light condition. Stomata of 24-H9 did not open by light in both intact leaves and epidermis, but the mutant guard cells normally showed blue light-induced activation of the H+ pump. Furthermore, expressions of the K+ channel KAT1 and AKT1 decreased 65% in guard cells of 24-H9. We performed map-based cloning and found that 24-H9 gene was the DWARF5 gene, which encodes one of the biosynthetic enzymes for phytohormone brassinosteroids. The results suggest that brassinosteroids may regulate the blue light-induced stomatal opening via upregulation of the K+ channels in guard cells.
