title: Induction of RAB18 gene expression and activation of K+ outward rectifying channels depend on an extracellular perception of ABA in Arabidopsis thaliana suspension cells.
abstract: Important progress has been made regarding the characterization of the ABA signalling components using genetic and molecular approaches (Leung and Giraudat, 1998). However, we do not yet know the mechanism of ABA perception. Conflicting results concerning the site of ABA perception have been published. The prevailing view is that since ABA controls many responses, different sites of perception for ABA might exist. In order to establish the cellular localisation of the ABA receptors in Arabidopsis thaliana suspension cells, we developed two physiological tests based upon the capacity of impermeant ABA-BSA conjugate to mimic permeant free ABA effects. We show that purified ABA-BSA conjugate is able to trigger RAB18 gene expression and that this response is strictly due to the natural (+)-ABA enantiomer. The rate of RAB18 gene expression was independent of the level of ABA uptake by the cells. Using the voltage-clamp technique we show that ABA-BSA, similarly to ABA, evokes a membrane depolarization and activates time- and voltage-dependent outward rectifying currents (ORC). We demonstrate that these ORC are due to a K+ efflux as assessed by tail currents and specific inhibition by both tetraethylammonium (TEA) and Ba2+. These observations provide evidence in favour of an extracellular site for ABA perception.
authors.affiliation: Laboratoire de Physiologie du Développement des Plantes, UMR CNRS 7632, Université Pierre et Marie Curie (Paris VI) France. ema@ccr.jussieu.fr
authors.forename: E
authors.initials: E
authors.lastname: Jeannette
authors.forename: J P
authors.initials: JP
authors.lastname: Rona
authors.forename: F
authors.initials: F
authors.lastname: Bardat
authors.forename: D
authors.initials: D
authors.lastname: Cornel
authors.forename: B
authors.initials: B
authors.lastname: Sotta
authors.forename: E
authors.initials: E
authors.lastname: Miginiac
mesh_terms: D000040:Abscisic Acid / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins; D002417:Cattle; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D006863:Hydrogen-Ion Concentration; D010940:Plant Proteins / Q000235:genetics*; D015221:Potassium Channels / Q000187:drug effects*; D012710:Serum Albumin, Bovine; D013237:Stereoisomerism; D020691:rab GTP-Binding Proteins
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; D015221:Potassium Channels; C078703:rab18 protein, Arabidopsis; D012710:Serum Albumin, Bovine; D000040:Abscisic Acid; D020691:rab GTP-Binding Proteins