Abscisic Acid Decreases Leaf Na + Exclusion in Salt-Treated Phaseolus vulgaris L. Catalina Cabot Æ John V. Sibole Æ Joan Barcelo ´ Æ Charlotte Poschenrieder Received: 6 October 2008 / Accepted: 19 January 2009 / Published online: 8 April 2009 Ó Springer Science+Business Media, LLC 2009 Abstract Previous results showed that in short-term NaCl- treated beans increased leaf abscisic acid (ABA) concen- tration was triggered by Na ? but not by Cl - . In this work, the specificity of ABA signaling for Na ? homeostasis was studied by comparing the plant’s responses to solutions that modified accumulation of ABA and/or Na ? uptake and distribution, such as supplemental Ca 2? , increased nutrient strength, different isosmotic composition, application of exogenous ABA, fluridone (an ABA inhibitor) and amino- oxiacetic acid (AOA, an ethylene inhibitor). After fluridone pretreatment, salt-treated beans had lower Na ? uptake and higher leaf Na ? exclusion capacity than non-pretreated plants. Moreover, Na ? uptake was increased and leaf Na ? exclusion was decreased by AOA and ABA. NaCl and KCl similarly increased leaf ABA and decreased transpiration rates, whereas supplemental Ca 2? and increased strength nutrient solution decreased leaf ABA and leaf Na ? . These results show (1) a non-ion-specific increase in ABA that probably signaled the osmotic component of salt, and (2) increased ABA levels that resulted in higher leaf Na ? con- centrations due to lower Na ? exclusion or increased root- shoot Na ? translocation. Keywords Abscisic acid Á Aminooxiacetic acid Á Bean Á Ethylene Á Fluridone Á Na ? exclusion Á Phaseolus Á Salinity Introduction Salinity causes important yield reduction in most cultivated plants due to the metabolic costs involved in the adaptation mechanisms to low soil water potential and the presence of high concentrations of toxic ions, principally Na ? and Cl - , in the soil solution. Even very salt-sensitive plants such as bean have maintained a certain capacity to respond to salinity. Beans have an efficient Na ? -exclusion mechanism that prevents toxic amounts of Na ? from reaching their leaves (Jacoby 1999 and references therein). Abscisic acid (ABA) is involved in the plant’s adapta- tion to osmotic stresses, participating, for instance, in the signaling events that lead to stomatal closure (Borel and others 2000; Mustili and others 2002); however, its role in other adaptative responses such as leaf growth inhibition remains controversial (Voisin and others 2006). Although much information is available on the role of ABA in reg- ulating ion fluxes in guard cells, little is known of ABA participation in the control of uptake and distribution of toxic ions such as Na ? . Previous results (Montero and others 1998; Sibole and others 1998) showed that in salt- treated beans there is a high positive correlation between leaf Na ? and xylem and leaf ABA, whereas no relationship was found between leaf ABA and leaf Cl - concentrations. Moreover, NaCl-pretreated bean plants showed improved growth when they were exposed to NaCl during later stages of their life cycle, and this improvement was related to their higher Na ? exclusion capacity and lower leaf ABA concentration with respect to non-NaCl-pretreated plants (Montero and others 1997). The aim of this work was to study the ABA signaling specificity for Na ? and its relative importance in the leaf Na ? exclusion mechanism of salt-treated bean plants by using different physiologic approaches. In the first series of C. Cabot (&) Á J. V. Sibole Department of Biology, Universitat de les Illes Balears, Ctra. Valldemossa km 7.5, 07122 Palma de Mallorca, Balearic Islands, Spain e-mail: ccabot@uib.es J. Barcelo ´ Á C. Poschenrieder Laboratory of Plant Physiology, Universitat Auto `noma de Barcelona, 08193 Bellaterra, Barcelona, Spain 123 J Plant Growth Regul (2009) 28:187–192 DOI 10.1007/s00344-009-9088-5