Abscisic Acid Decreases Leaf Na+ Exclusion in Salt-Treated Phaseolus vulgaris L.

Previous results showed that in short-term NaCl-treated beans increased leaf abscisic acid (ABA) concentration 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 Ca2+, increased nutrient strength, different isosmotic composition, application of exogenous ABA, fluridone (an ABA inhibitor) and aminooxiacetic 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 Ca2+ 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+ concentrations due to lower Na+ exclusion or increased root-shoot Na+ translocation.