CO2 provides an intermediate link in the red light response of guard cells

Authors

  • M. Rob G. Roelfsema,

    1. Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany
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  • Stefan Hanstein,

    1. Botanisches Institut I, Universität Gießen, Senckenbergstaße 17, D-35390 Gießen, Germany
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  • Hubert H. Felle,

    1. Botanisches Institut I, Universität Gießen, Senckenbergstaße 17, D-35390 Gießen, Germany
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  • Rainer Hedrich

    Corresponding author
    1. Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany
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* For correspondence (fax +49 931 8886157; e-mail hedrich@botanik.uni.wuezburg.de).

Summary

Guard cells in intact leafs display light-induced membrane potential changes, which alter the direction of K+-transport across the plasma membrane (Roelfsema et al., 2001). A beam of blue light, but not red light, directed at the impaled guard cell triggers this response, while both light qualities induce opening of stomata. To gain insight into this apparent contradiction, we explored the possible interaction between red light and CO2. Guard cells in the intact plant were impaled with double-barrelled electrodes and illuminated with red light. Cells that were hyperpolarized in CO2-free air, depolarized after a switch to air with 700 µl l−1 CO2, in a reversible manner. As a result, K+-fluxes across the plasma membrane changed direction, to favour K+ extrusion and stomatal closure in the presence of CO2. Concurrent with the depolarization, an inward current across the plasma membrane appeared, most likely due to activation of anion channels. Guard cell responses to CO2 could be recorded in darkness as well as in red light. However, in darkness some cells spontaneously depolarized, these cells hyperpolarized again in red light. Here, red light was projected on a large area of the leaf and decreased the intracellular CO2 concentration by about 250 µl l−1, as measured with a miniature CO2 sensor placed in the substomatal cavity. We conclude, that in intact leaves the red light response of guard cells is mediated through a decrease of the intercellular CO2 concentration.

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