title: A new role for an old enzyme: nitrate reductase-mediated nitric oxide generation is required for abscisic acid-induced stomatal closure in Arabidopsis thaliana.
abstract: The plant hormone abscisic acid (ABA), synthesized in response to water-deficit stress, induces stomatal closure via activation of complex signaling cascades. Recent work has established that nitric oxide (NO) is a key signaling molecule mediating ABA-induced stomatal closure. However, the biosynthetic origin of NO in guard cells has not yet been resolved. Here, we provide pharmacological, physiological, and genetic evidence that NO synthesis in Arabidopsis guard cells is mediated by the enzyme nitrate reductase (NR). Guard cells of wild-type Arabidopsis generate NO in response to treatment with ABA and nitrite, a substrate for NR. Moreover, NR-mediated NO synthesis is required for ABA-induced stomatal closure. However, in the NR double mutant, nia1, nia2 that has diminished NR activity, guard cells do not synthesize NO nor do the stomata close in response to ABA or nitrite, although stomatal opening is still inhibited by ABA. Furthermore, by using the ABA-insensitive (ABI) abi1-1 and abi2-1 mutants, we show that the ABI1 and ABI2 protein phosphatases are downstream of NO in the ABA signal-transduction cascade. These data demonstrate a previously uncharacterized signaling role for NR, that of mediating ABA-induced NO synthesis in Arabidopsis guard cells.
authors.affiliation: Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol BS16 1QY, United Kingdom, Europe.
authors.forename: Radhika
authors.initials: R
authors.lastname: Desikan
authors.forename: Rachael
authors.initials: R
authors.lastname: Griffiths
authors.forename: John
authors.initials: J
authors.lastname: Hancock
authors.forename: Steven
authors.initials: S
authors.lastname: Neill
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000502:physiology*; D009569:Nitric Oxide / Q000096:biosynthesis / Q000494:pharmacology / Q000502:physiology*; D009573:Nitrites / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D009573:Nitrites; D009569:Nitric Oxide; D000040:Abscisic Acid; D009565:Nitrate Reductases; D050901:Nitrate Reductase; C087434:ABI1 protein, Arabidopsis; C106443:ABI2 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases