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.