title: Nitric oxide, stomatal closure, and abiotic stress.
abstract: Various data indicate that nitric oxide (NO) is an endogenous signal in plants that mediates responses to several stimuli. Experimental evidence in support of such signalling roles for NO has been obtained via the application of NO, usually in the form of NO donors, via the measurement of endogenous NO, and through the manipulation of endogenous NO content by chemical and genetic means. Stomatal closure, initiated by abscisic acid (ABA), is effected through a complex symphony of intracellular signalling in which NO appears to be one component. Exogenous NO induces stomatal closure, ABA triggers NO generation, removal of NO by scavengers inhibits stomatal closure in response to ABA, and ABA-induced stomatal closure is reduced in mutants that are impaired in NO generation. The data indicate that ABA-induced guard cell NO generation requires both nitric oxide synthase-like activity and, in Arabidopsis, the NIA1 isoform of nitrate reductase (NR). NO stimulates mitogen-activated protein kinase (MAPK) activity and cGMP production. Both these NO-stimulated events are required for ABA-induced stomatal closure. ABA also stimulates the generation of H2O2 in guard cells, and pharmacological and genetic data demonstrate that NO accumulation in these cells is dependent on such production. Recent data have extended this model to maize mesophyll cells where the induction of antioxidant defences by water stress and ABA required the generation of H2O2 and NO and the activation of a MAPK. Published data suggest that drought and salinity induce NO generation which activates cellular processes that afford some protection against the oxidative stress associated with these conditions. Exogenous NO can also protect cells against oxidative stress. Thus, the data suggest an emerging model of stress responses in which ABA has several ameliorative functions. These include the rapid induction of stomatal closure to reduce transpirational water loss and the activation of antioxidant defences to combat oxidative stress. These are two processes that both involve NO as a key signalling intermediate.
authors.affiliation: Centre for Research in Plant Science, Faculty of Health and Life Sciences, University of the West of England, Bristol BS16 1QY, UK. Steven.Neill@uwe.ac.uk
authors.forename: Steven
authors.initials: S
authors.lastname: Neill
authors.forename: Raimundo
authors.initials: R
authors.lastname: Barros
authors.forename: Jo
authors.initials: J
authors.lastname: Bright
authors.forename: Radhika
authors.initials: R
authors.lastname: Desikan
authors.forename: John
authors.initials: J
authors.lastname: Hancock
authors.forename: Judith
authors.initials: J
authors.lastname: Harrison
authors.forename: Peter
authors.initials: P
authors.lastname: Morris
authors.forename: Dimas
authors.initials: D
authors.lastname: Ribeiro
authors.forename: Ian
authors.initials: I
authors.lastname: Wilson
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D000222:Adaptation, Physiological; D000975:Antioxidants / Q000502:physiology; D017360:Arabidopsis / Q000378:metabolism* / Q000382:microbiology / Q000502:physiology; D006861:Hydrogen Peroxide / Q000378:metabolism; D008027:Light; D009569:Nitric Oxide / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology; D010935:Plant Diseases; D054046:Plant Stomata / Q000382:microbiology / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D014867:Water / Q000378:metabolism
chemical_list: D000975:Antioxidants; D014867:Water; D009569:Nitric Oxide; D000040:Abscisic Acid; D006861:Hydrogen Peroxide