title: Abscisic acid negatively interferes with basal defence of barley against Magnaporthe oryzae.
abstract: BACKGROUND
  Plant hormones are well known regulators which balance plant responses to abiotic and biotic stresses. We investigated the role of abscisic acid (ABA) in resistance of barley (Hordeum vulgare L.) against the plant pathogenic fungus Magnaporthe oryzae.
  
  
  RESULTS
  Exogenous application of ABA prior to inoculation with M. oryzae led to more disease symptoms on barley leaves. This result contrasted the finding that ABA application enhances resistance of barley against the powdery mildew fungus. Microscopic analysis identified diminished penetration resistance as cause for enhanced susceptibility. Consistently, the barley mutant Az34, impaired in ABA biosynthesis, was less susceptible to infection by M. oryzae and displayed elevated penetration resistance as compared to the isogenic wild type cultivar Steptoe. Chemical complementation of Az34 mutant plants by exogenous application of ABA re-established disease severity to the wild type level. The role of ABA in susceptibility of barley against M. oryzae was corroborated by showing that ABA application led to increased disease severity in all barley cultivars under investigation except for the most susceptible cultivar Pallas. Interestingly, endogenous ABA concentrations did not significantly change after infection of barley with M. oryzae.
  
  
  CONCLUSIONS
  Our results revealed that elevated ABA levels led to a higher disease severity on barley leaves to M. oryzae. This supports earlier reports on the role of ABA in enhancing susceptibility of rice to the same pathogen and thereby demonstrates a host plant-independent function of this phytohormone in pathogenicity of monocotyledonous plants against M. oryzae.
authors.affiliation: Department of Plant Physiology, RWTH Aachen University, 52056, Aachen, Germany. sylvia.ulferts@gmx.de.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Ulferts
authors.affiliation: Department of Plant Physiology, RWTH Aachen University, 52056, Aachen, Germany. delventhal@bio3.rwth-aachen.de.
authors.forename: Rhoda
authors.initials: R
authors.lastname: Delventhal
authors.affiliation: Institute for Molecular Biosciences, Goethe University of Frankfurt, 60438, Frankfurt am Main, Germany. richard.splivallo@a3.epfl.ch.
authors.forename: Richard
authors.initials: R
authors.lastname: Splivallo
authors.affiliation: Molecular Phytopathology and Mycotoxin Research, University of Goettingen, Grisebachstrasse 6, 37077, Goettingen, Germany. pkarlov@gwdg.de.
authors.forename: Petr
authors.initials: P
authors.lastname: Karlovsky
authors.affiliation: Department of Plant Physiology, RWTH Aachen University, 52056, Aachen, Germany. schaffrath@bio3.rwth-aachen.de.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schaffrath
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D060467:Disease Resistance / Q000187:drug effects; D005838:Genotype; D001467:Hordeum / Q000187:drug effects / Q000235:genetics / Q000276:immunology* / Q000382:microbiology*; D007700:Kinetics; D020082:Magnaporthe / Q000187:drug effects / Q000502:physiology*; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology*; D010937:Plant Growth Regulators / Q000494:pharmacology; D020156:Salicylic Acid / Q000378:metabolism
chemical_list: D010937:Plant Growth Regulators; D000040:Abscisic Acid; D020156:Salicylic Acid