title: NH4+ protects tomato plants against Pseudomonas syringae by activation of systemic acquired acclimation.
abstract: NH4 (+) nutrition provokes mild toxicity by enhancing H2O2 accumulation, which acts as a signal activating systemic acquired acclimation (SAA). Until now, induced resistance mechanisms in response to an abiotic stimulus and related to SAA were only reported for exposure to a subsequent abiotic stress. Herein, the first evidence is provided that this acclimation to an abiotic stimulus induces resistance to later pathogen infection, since NH4 (+) nutrition (N-NH4 (+))-induced resistance (NH4 (+)-IR) against Pseudomonas syringae pv tomato DC3000 (Pst) in tomato plants was demonstrated. N-NH4 (+) plants displayed basal H2O2, abscisic acid (ABA), and putrescine (Put) accumulation. H2O2 accumulation acted as a signal to induce ABA-dependent signalling pathways required to prevent NH4 (+) toxicity. This acclimatory event provoked an increase in resistance against later pathogen infection. N-NH4 (+) plants displayed basal stomatal closure produced by H2O2 derived from enhanced CuAO and rboh1 activity that may reduce the entry of bacteria into the mesophyll, diminishing the disease symptoms as well as strongly inducing the oxidative burst upon Pst infection, favouring NH4 (+)-IR. Experiments with inhibitors of Put accumulation and the ABA-deficient mutant flacca demonstrated that Put and ABA downstream signalling pathways are required to complete NH4 (+)-IR. The metabolic profile revealed that infected N-NH4 (+) plants showed greater ferulic acid accumulation compared with control plants. Although classical salicylic acid (SA)-dependent responses against biotrophic pathogens were not found, the important role of Put in the resistance of tomato against Pst was demonstrated. Moreover, this work revealed the cross-talk between abiotic stress acclimation (NH4 (+) nutrition) and resistance to subsequent Pst infection.
authors.affiliation: Grupo de Bioquímica y Biotecnología, Área de Fisiología Vegetal, Departamento de Ciencias Agrarias y del Medio Natural, ESTCE. Universitat Jaume I, 12071 Castellón, Spain.
authors.forename: Emma
authors.initials: E
authors.lastname: Fernández-Crespo
authors.affiliation: Grupo de Bioquímica y Biotecnología, Área de Fisiología Vegetal, Departamento de Ciencias Agrarias y del Medio Natural, ESTCE. Universitat Jaume I, 12071 Castellón, Spain.
authors.forename: Loredana
authors.initials: L
authors.lastname: Scalschi
authors.affiliation: Grupo de Bioquímica y Biotecnología, Área de Fisiología Vegetal, Departamento de Ciencias Agrarias y del Medio Natural, ESTCE. Universitat Jaume I, 12071 Castellón, Spain.
authors.forename: Eugenio
authors.identifier: http://orcid.org/0000-0003-1931-1071
authors.initials: E
authors.lastname: Llorens
authors.affiliation: Grupo de Bioquímica y Biotecnología, Área de Fisiología Vegetal, Departamento de Ciencias Agrarias y del Medio Natural, ESTCE. Universitat Jaume I, 12071 Castellón, Spain.
authors.forename: Pilar
authors.initials: P
authors.lastname: García-Agustín
authors.affiliation: Grupo de Bioquímica y Biotecnología, Área de Fisiología Vegetal, Departamento de Ciencias Agrarias y del Medio Natural, ESTCE. Universitat Jaume I, 12071 Castellón, Spain camanes@uji.es.
authors.forename: Gemma
authors.identifier: http://orcid.org/0000-0001-6407-9246
authors.initials: G
authors.lastname: Camañes
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D000064:Acclimatization; D064751:Ammonium Compounds / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D018551:Solanum lycopersicum / Q000276:immunology / Q000382:microbiology / Q000502:physiology*; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D057865:Plant Immunity; D018521:Plant Physiological Phenomena; D044224:Pseudomonas syringae / Q000502:physiology*; D011700:Putrescine / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D064751:Ammonium Compounds; D000040:Abscisic Acid; D006861:Hydrogen Peroxide; D011700:Putrescine
keywords: ABA; H2O2; NH4
  + nutrition; induced resistance; putrescine; systemic acquired acclimation.