title: Barley mildew and its elicitor chitosan promote closed stomata by stimulating guard-cell S-type anion channels.
abstract: Stomatal closure is known to be associated with early defence responses of plant cells triggered by microbe-associated molecular patterns (MAMPs). However, the molecular mechanisms underlying these guard-cell responses have not yet been elucidated. We therefore studied pathogen-induced changes in ion channel activity in Hordeum vulgare guard cells. Barley mildew (Blumeria graminis) hyphae growing on leaves inhibited light-induced stomatal opening, starting at 9 h after inoculation, when appressoria had developed. Alternatively, stomatal closure was induced by nano-infusion of chitosan via open stomata into the sub-stomatal cavity. Experiments using intracellular double-barreled micro-electrodes revealed that mildew stimulated S-type (slow) anion channels in guard cells. These channels enable the efflux of anions from guard cells and also promote K(+) extrusion by altering the plasma membrane potential. Stimulation of S-type anion channels was also provoked by nano-infusion of chitosan. These data suggest that MAMPs of mildew hyphae penetrating the cuticle provoke activation of S-type anion channels in guard cells. In response, guard cells extrude K(+) salts, resulting in stomatal closure. Plasma membrane anion channels probably represent general targets of MAMP signaling in plants, as these elicitors depolarize the plasma membrane of various cell types.
authors.affiliation: Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Biosciences, Biocenter, Würzburg University, Julius-von-Sachs Platz 2, D-97082 Würzburg, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Koers
authors.forename: Aysin
authors.initials: A
authors.lastname: Guzel-Deger
authors.forename: Irene
authors.initials: I
authors.lastname: Marten
authors.forename: M Rob G
authors.initials: MR
authors.lastname: Roelfsema
mesh_terms: D001203:Ascomycota / Q000502:physiology*; D048271:Chitosan / Q000378:metabolism*; D001467:Hordeum / Q000378:metabolism / Q000382:microbiology*; D054884:Host-Pathogen Interactions; D025301:Hyphae / Q000502:physiology; D015640:Ion Channel Gating; D007473:Ion Channels / Q000378:metabolism; D008564:Membrane Potentials; D010935:Plant Diseases / Q000382:microbiology; D054046:Plant Stomata / Q000378:metabolism / Q000382:microbiology*; D011188:Potassium / Q000378:metabolism
chemical_list: D007473:Ion Channels; D048271:Chitosan; D011188:Potassium