Chemi-osmotic extrusion of protons, blue light and stomatal movement


Photo credit: Google

Faba bean (Vicia faba)

Blue light-dependent proton extrusion by guard-cell protoplasts of Vicia faba.

by Shimazaki K., Iino M., Zeiger E. (1986)

Department of Biological Sciences, Stanford University, Stanford, California 94305, USA
Carnegie Institution of Washington, Department of Plant Biology, 290 Panama Street, Stanford, California 94305, USA

in Nature 319, 324326 (1986) -doi:10.1038/319324a0 –



In plant leaves, light regulation of stomatal movement, and hence of gas exchange1, involves a non-photosynthetic photosensory system sensitive to blue light2–6, which transduces many other plant movement responses.

The exact nature of the primary photo-reactions of this system is still not known7.

Stomatal opening is, in general, based on swelling of the guard cells driven by ion uptake1, and it has been suggested that energy for such uptake may be provided by a chemi-osmotic extrusion of protons across the plasmalemma1,8,9.

We report here that guard-cell protoplasts from Vicia faba, irradiated continuously with photosynthetically saturating, high-fluence-rate red light, extrude H+ ions in response to a short pulse (30s) of blue light. The response is relatively long-lived, such that a high rate of H+ extrusion continues for several minutes after the pulse stimulation, indicating that continuous input of blue light energy is not required for a sustained response.

The kinetic relation between pulse input and response output matched closely that found for the stomatal response in intact leaves6.

In agreement with the chemi-osmotic hypothesis, activation of an electrogenic plasmalemma H+-ATPase is postulated as the cause of blue light-induced H+ extrusion.


Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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