Department of Botany I - Plant-Physiology and Biophysics

    Guard cell responses to biotic signals

    Stomata are pores within the leaf surface, which enable gas exchange between the plant and the atmosphere. These stomata, however, also provide potential penetration sides for pathogenic microorganisms. We were able to show, that mildew infection provokes stomatal closure in barley leaves. This response could be simulated by nano-infusion injection of chitosan, which is a component of fungal cell walls (Fig.; Koers et al., 2011).

    In the model plant Arabidopsis, rapid stomatal closure is provoked by flg22, a peptide derived from the flagella protein of the pathogenic bacteria Pseudomonas syringae. With the aid of selected Arabidopsis mutants, we found that flg22 activates channels in guard cells, which facilitate the release of anions (Guzel Deger et al., 2015). Activation of these anion channels initiates loss of potassium salts from guard cells and causes stomatal closure. In a current project, we compare the signaling mechanisms activated by pathogens, with those targeted by the drought hormone ABA. The results of this project potentially can be used to improve pathogen resistance and the efficiency of water usage in crop plants.

    After infusion of chitosan into barley leaves, stomata close within 20 minutes, whereas stomata remain open after infusion of control solution.
    Stomatal closure in barley leaves, triggered by nano-infusion of chitosan. (A) Superposition of the transmitted light‑ and fluorescence images, directly after nano-infusion of chitosan and Lucifer Yellow in the sub-stomatal cavity. (t= 10 min.), and 12 minutes later (t = 22 min.). (B) Stomatal apertures determined before and after (t = 10 min.) nano-infusion of chitosan (symbol ● in B) or control solution (symbol о in B). Data were normalized for the apertures at t=10 min., error bars represent SE, n=11-19. Data from Koers et al., 2011.
    (Graphic: R. Roelfsema, S. Koers, Universität Würzburg 2011)

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