title: Chloride-inducible transient apoplastic alkalinizations induce stomata closure by controlling abscisic acid distribution between leaf apoplast and guard cells in salt-stressed Vicia faba.
abstract: Chloride stress causes the leaf apoplast transiently to alkalize, an event that is presumed to contribute to the ability of plants to adapt to saline conditions. However, the initiation of coordinated processes downstream of the alkalinization is unknown. We hypothesize that chloride-inducible pH dynamics are a key chemical feature modulating the compartmental distribution of abscisic acid (ABA) and, as a consequence, affecting stomata aperture. Apoplastic pH and stomata aperture dynamics in intact Vicia faba leaves were monitored by microscopy-based ratio imaging and porometric measurements of stomatal conductance. ABA concentrations in leaf apoplast and guard cells were compared with pH dynamics by gas-chromatography-mass-spectrometry (GC-MS) and liquid-chromatography-tandem-mass spectrometry (LC-MS/MS). Results demonstrate that, upon chloride addition to roots, an alkalizing factor that initiates the pH dynamic propagates from root to leaf in a way similar to xylem-distributed water. In leaves, it induces a systemic transient apoplastic alkalinization that causes apoplastic ABA concentration to increase, followed by an elevation of endogenous guard cell ABA. We conclude that the transient alkalinization, which is a remote effect of chloride stress, modulates the compartmental distribution of ABA between the leaf apoplast and the guard cells and, in this way, is instrumental in inducing stomata closure during the beginning of salinity.
authors.affiliation: Institute of Plant Nutrition and Soil Science, Christian Albrechts University, Hermann-Rodewald-Str. 2, D-24118, Kiel, Germany.
authors.forename: Christoph-Martin
authors.initials: CM
authors.lastname: Geilfus
authors.affiliation: Department Bioorganic Chemistry, Max Planck Institute for Chemical Ecology, Hans-Knöll-Straße 8, D-07745, Jena, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Mithöfer
authors.affiliation: Institut für Botanik, Technische Universität Dresden, Zellescher Weg 20b, D-01062, Dresden, Germany.
authors.forename: Jutta
authors.initials: J
authors.lastname: Ludwig-Müller
authors.affiliation: Institute of Crop Science, Quality of Plant Products, University Hohenheim, Schloss, Westhof West, 118, D-70593, Stuttgart, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Zörb
authors.affiliation: Institute of Plant Nutrition and Soil Science, Christian Albrechts University, Hermann-Rodewald-Str. 2, D-24118, Kiel, Germany.
authors.forename: Karl H
authors.initials: KH
authors.lastname: Muehling
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D018517:Plant Roots / Q000378:metabolism; D054046:Plant Stomata / Q000502:physiology*; D058526:Plant Vascular Bundle / Q000378:metabolism; D054712:Salinity; D013312:Stress, Physiological; D031307:Vicia faba / Q000502:physiology*
chemical_list: D002712:Chlorides; D000040:Abscisic Acid
keywords: Vicia faba; abscisic acid (ABA); apoplastic pH; chloride; guard cell; salinity; stomata