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WHOLE PLANT AND ECOPHYSIOLOGY

The Stomata of the Fern Adiantum capillus-veneris Do Not Respond to CO₂ in the Dark and Open by Photosynthesis in Guard Cells^1,[OA]

Center for Research and Advancement in Higher Education (M.D.), and Department of Biology, Faculty of Science (K.S.), Kyushu University, Ropponmatsu, Fukuoka 810–8560, Japan

The stomata of the fern Adiantum capillus-veneris lack a blue light-specific opening response but open in response to red light. We investigated this light response of Adiantum stomata and found that the light wavelength dependence of stomatal opening matched that of photosynthesis. The simultaneous application of red (2 µmol m^–2 s^–1) and far-red (50 µmol m^–2 s^–1) light synergistically induced stomatal opening, but application of only one of these wavelengths was ineffective. Adiantum stomata did not respond to CO₂ in the dark; the stomata neither opened under a low intercellular CO₂ concentration nor closed under high intercellular CO₂ concentration. Stomata in Arabidopsis (Arabidopsis thaliana), which were used as a control, showed clear sensitivity to CO₂. In Adiantum, stomatal conductance showed much higher light sensitivity when the light was applied to the lower leaf surface, where stomata exist, than when it was applied to the upper surface. This suggests that guard cells likely sensed the light required for stomatal opening. In the epidermal fragments, red light induced both stomatal opening and K⁺ accumulation in guard cells, and both of these responses were inhibited by a photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The stomatal opening was completely inhibited by CsCl, a K⁺ channel blocker. In intact fern leaves, red light-induced stomatal opening was also suppressed by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. These results indicate that Adiantum stomata lack sensitivity to CO₂ in the dark and that stomatal opening is driven by photosynthetic electron transport in guard cell chloroplasts, probably via K⁺ uptake.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Ken-ichiro Shimazaki (kenrcb{at}mbox.nc.kyushu-u.ac.jp).

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.118950

^* Corresponding author; e-mail kenrcb{at}mbox.nc.kyushu-u.ac.jp.

Received March 11, 2008; accepted April 13, 2008; published May 8, 2008.

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