title: Fungal membrane responses induced by plant defensins and thionins.
abstract: Treatment of hyphae of Neurospora crassa with antifungal plant defensins, i.e. Rs-AFP2 and Dm-AMP1 isolated from radish and dahlia seed, respectively, induced a rapid K+ efflux, Ca2+ uptake, and alkalinization of the incubation medium. The Rs-AFP2-induced alkalinization of the incubation medium could be inhibited with G-protein inhibitors. alpha-Hordothionin, an antifungal thionin from barley seed, caused a sustained increased Ca2+ uptake at subinhibitory concentrations but only a transient increased uptake at inhibitory concentrations. alpha-Hordothionin also caused increased K+ efflux and alkalinization of the medium, but these fluxes occurred more rapidly compared to those caused by plant defensins. Furthermore, alpha-hordothionin caused permeabilization of fungal hyphae to the non-metabolite alpha-aminoisobutyric acid and, in addition, altered the electrical properties of artificial lipid bilayers, consistently leading to rupture of the lipid bilayers. The plant defensins did not form ion-permeable pores in artificial membranes and did not exhibit substantial hyphal membrane permeabilization activity. Our results are consistent with the notion that thionins inhibit fungal growth as a result of direct protein-membrane interactions, whereas plant defensins might act via a different, possibly receptor-mediated, mechanism.
authors.affiliation: F. A. Janssens Laboratory of Genetics, Katholieke Universiteit Leuven, Willem de Croylaan 42, B-3001 Heverlee, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Thevissen
authors.forename: A
authors.initials: A
authors.lastname: Ghazi
authors.forename: G W
authors.initials: GW
authors.lastname: De Samblanx
authors.forename: C
authors.initials: C
authors.lastname: Brownlee
authors.forename: R W
authors.initials: RW
authors.lastname: Osborn
authors.forename: W F
authors.initials: WF
authors.lastname: Broekaert
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D023082:Defensins; D005670:Fusarium / Q000187:drug effects / Q000378:metabolism*; D001467:Hordeum; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000187:drug effects; D009492:Neurospora crassa / Q000187:drug effects / Q000378:metabolism*; D010940:Plant Proteins / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D012639:Seeds
chemical_list: D000935:Antifungal Agents; D023181:Antimicrobial Cationic Peptides; D023082:Defensins; C099969:Dm-AMP1 protein, Dahlia merckii; D008051:Lipid Bilayers; D010940:Plant Proteins; C036092:hordothionin protein, Hordeum vulgare; D011188:Potassium; D002118:Calcium