title: [The ABC of abscisic acid action in plant drought stress             responses].
abstract: The combined daily consumption of fresh water ranges from 200 to 700 liters per             capita per day in most developed countries, with about 70% being used for           agricultural needs. Unlike other resources such as the different forms of energy, water           has no other alternatives. With the looming prospect of global water crisis, the recent           laudable success in deciphering the early steps in the signal transduction of the "stress           hormone" abscisic acid (ABA) has ignited hopes that crops can be engineered with the           capacity to maintain productivity while requiring less water input. Although ABA was first           discovered in plants, it has resurfaced in the human brain (and many other non-plant           organisms : sea sponge, some parasites, hydra to name a few), suggesting that its           existence may be widespread. In humans, more amazingly, ABA has shown anti-inflammatory           and antiviral properties. Even its receptors and key signaling intermediates have homologs           in the human genome suggesting that evolution has re-fashioned these same proteins into           new functional contexts. Thus, learning about the molecular mechanisms of ABA in action           using the more flexible plant model will be likely beneficial to other organisms, and           especially in human diseases, which is topical in the medical circle. ABA can accumulate           up to 10 to 30-fold in plants under drought stress relative to unstressed conditions. The           built up of the hormone then triggers diverse adaptive pathways permitting plants to           withstand temporary bouts of water shortage. One favorite experimental model to unravel           ABA signaling mechanisms in all of its intimate detail is based on the hormone's ability           to elicit stomatal closure - a rapid cellular response of land plants to limit water loss           through transpiration. Each microscopic stoma, or pore, is contoured by two specialized           kidney-shaped cells called the guard cells. Because land plants are protected by a waxy           cuticle impermeable to gas exchange, the stomatal pores are thus the primary portals for           photosynthetic CO(2) uptake. Drought, by biasing pathways that lead to rapid           closure of these pores, has therefore a negative impact on photosynthesis, and           consequently, biomass as well. The stomatal aperture widens and narrows by expansion and           contraction, respectively, of these flanking guard cells caused by changes in the           intracellular concentrations of ion fluxes. These transport mechanisms most likely share           fundamental principles with any excitable cell. These events require coordination of           channels, vacuolar and membrane transporters that generate a specific pattern of           electrical signals that relay the ABA stimulus. Research on ABA begun in the 1960's has           now been crowned by the achievement of having identified the soluble ABA receptor that           turns on and off the activities of a kinase/phosphatase pair, as the heart of the           signaling complex. Results distilled from the latest structural studies on these ABA           receptors, characterized by the so-called START domain, are beginning to tender the most           exciting promise for rational design of agonists and antagonists towards modulating stress           adaptive ability in plants. This review will chart the recent extraordinary progress that           has enlightened us on how ABA controls membrane transport mechanisms that evoke the fast           stomatal closing pathway.
authors: Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, Unité Propre de Recherche 2355, 1 Avenue de la Terrasse Bât. 23, 91198 Gif-sur-Yvette Cedex, France. Leung@isv.cnrs-gif.fr
authors: Jeffrey
authors: J
authors: Leung
authors: Christiane
authors: C
authors: Valon
authors: Bertrand
authors: B
authors: Moreau
authors: Martin
authors: M
authors: Boeglin
authors: Cécile
authors: C
authors: Lefoulon
authors: Archana
authors: A
authors: Joshi-Saha
authors: Isabelle
authors: I
authors: Chérel
mesh_terms: D000040:Abscisic Acid / Q000502:physiology*; D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D055864:Droughts; D006801:Humans; D010788:Photosynthesis / Q000502:physiology; D018521:Plant Physiological Phenomena; D054046:Plant Stomata / Q000502:physiology; D010944:Plants / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology*; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D000040:Abscisic Acid