title: Kinetics of NH                         (4)                                   (+)                       uptake by the arbuscular mycorrhizal fungus Rhizophagus irregularis.
abstract: The kinetics and energetics of (15)NH                            (4)                                      (+)                          uptake by the extraradical mycelium of the arbuscular mycorrhizal fungus Rhizophagus irregularis were investigated. (15)NH                            (4)                                      (+)                          uptake increased with increasing substrate concentration over the concentration range of 0.002 to 25 mM. Eadie-Hofstee plots showed that ammonium (NH                            (4)                                      (+)                         ) uptake over this range was biphasic. At concentrations below 100 μM, NH                            (4)                                      (+)                          uptake fits a Michaelis-Menten curve, typical of the activity of a saturable high-affinity transport system (HATS). At concentrations above 1 mM, NH                            (4)                                      (+)                          influx showed a linear response typical of a nonsaturable low-affinity transport system (LATS). Both transport systems were dependent on external pH. The HATS and, to a lesser extent, the LATS were inhibited by the ionophore carbonylcyanide m-chlorophenylhydrazone (CCCP) and the ATP-synthesis inhibitor 2,4-dinitrophenol. These data indicate that the two NH                            (4)                                      (+)                          transport systems of R. irregularis are dependent on metabolic energy and on the electrochemical H(+) gradient. The HATS- and the LATS-mediated (15)NH                            (4)                                      (+)                          influxes were also regulated by acetate. This first report of the existence of active high- and low-affinity NH4(+) transport systems in the extraradical mycelium of an arbuscular mycorrhizal fungus and provides novel information on the mechanisms underlying mycosymbiont uptake of nitrogen from the soil environment.
authors: Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008, Granada, Spain.
authors: J
authors: J
authors: Pérez-Tienda
authors: A
authors: A
authors: Valderas
authors: G
authors: G
authors: Camañes
authors: P
authors: P
authors: García-Agustín
authors: N
authors: N
authors: Ferrol
mesh_terms: D019297:2,4-Dinitrophenol / Q000494:pharmacology; D000085:Acetates / Q000494:pharmacology*; D064751:Ammonium Compounds / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D018552:Daucus carota / Q000378:metabolism / Q000382:microbiology*; D004305:Dose-Response Relationship, Drug; D055137:Glomeromycota / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D025282:Mycelium / Q000187:drug effects / Q000378:metabolism; D038821:Mycorrhizae / Q000187:drug effects / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D009587:Nitrogen Isotopes; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology
chemical_list: D000085:Acetates; D064751:Ammonium Compounds; D009587:Nitrogen Isotopes; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D009584:Nitrogen; D019297:2,4-Dinitrophenol