Abstract
Stomata in Adiantum capillus-veneris lack blue light-specific response, but open in response to light. We investigated this light response in intact leaves. The spectrum for stomatal opening matched to photosynthesis. The application of red and far-red light induced the synergism of stomatal opening. Stomata in Adiantum lacked the CO2 sensitivity in dark. Stomatal conductance showed the much higher sensitivity to light when it was applied to the lower leaf surface, where stomata exist, than applied to the upper surface, suggesting that guard cells sensed the light. In isolated epidermis, red light induced stomatal opening and K+ accumulation in guard cells, and photosynthetic inhibitor inhibited both of them. Red light-induced stomatal opening was completely inhibited by CsCl, a K+ channel blocker. These results indicate that Adiantum stomata lack the sensitivity to CO2 and that the opening is driven by photosynthesis in guard cell chloroplasts, probably via K+ uptake.