title: Isohydric and anisohydric strategies of wheat genotypes under osmotic stress: biosynthesis and function of ABA in stress responses.
abstract: Changes in water potential (ψw), stomatal conductance, abscisic acid (ABA) accumulation, expression of the major genes involved in ABA biosynthesis, activities of abscisic aldehyde oxidase (AO, EC 1.2.3.1) and antioxidant enzymes were studied in two wheat cultivars with contrasting acclimation strategies subjected to medium strength osmotic stress (-0.976MPa) induced by polyethylene glycol (PEG 6000). Because the biosynthetic pathway of ABA involves multiple gene products, the aim of this study was to unravel how these genes are regulated in isohydric and anisohydric wheat genotypes. In the root tissues of the isohydric cultivar, Triticum aestivum cv. Kobomugi, osmotic stress increased the transcript levels of 9-cis-epoxycarotenoid dioxygenase (NCED) gene, controlling the rate limiting step of ABA biosynthesis. Moreover, this cultivar exhibited a higher basal activity and a higher induction of aldehyde oxidase isoenzymes (AAO2-AAO3), responsible for converting ABAldehyde to ABA. It was found that the fast activation of the ABA biosynthesis in the roots generated an enhanced ABA pool in the shoot, which brought about a faster closure of the stomata upon increasing osmotic stress and, as a result, the plants could maintain ψw in the tissues close to the control level. In contrast, the anisohydric genotype, cv. GK Öthalom, exhibited a moderate induction of ABA biosynthesis in the roots, leading to the maintenance but no increase in the concentration of ABA on the basis of tissue water content in the leaves. Due to the slower response of their stomata to water deficit, the tissues of cv. GK Öthalom have to acclimate to much more negative water potentials during increasing osmotic stress. A decreased activity of superoxide dismutase (SOD) was found in the leaves and roots of both cultivars exposed to osmotic stress, but in the roots elevated activities of catalase (CAT), peroxidase (POX), glutathione reductase (GR) and glutathione transferase (GST) were detected in the isohydric cultivar, suggesting that this genotype was more successful in the elimination of reactive oxygen species caused by the stress conditions.
authors.affiliation: Department of Plant Biology, University of Szeged, H-6701 Szeged, Közép fasor 52., P.O. Box 654, Hungary. Electronic address: galleagnes@gmail.com.
authors.forename: Ágnes
authors.initials: Á
authors.lastname: Gallé
authors.forename: Jolán
authors.initials: J
authors.lastname: Csiszár
authors.forename: Dániel
authors.initials: D
authors.lastname: Benyó
authors.forename: Gábor
authors.initials: G
authors.lastname: Laskay
authors.forename: Tünde
authors.initials: T
authors.lastname: Leviczky
authors.forename: László
authors.initials: L
authors.lastname: Erdei
authors.forename: Irma
authors.initials: I
authors.lastname: Tari
mesh_terms: D000040:Abscisic Acid / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D000064:Acclimatization; D042931:Aldehyde Oxidase / Q000235:genetics / Q000378:metabolism; D000975:Antioxidants / Q000378:metabolism; D001692:Biological Transport; D003890:Desiccation; D004797:Enzyme-Linked Immunosorbent Assay; D018506:Gene Expression Regulation, Plant; D009997:Osmotic Pressure; D054046:Plant Stomata / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D014908:Triticum / Q000235:genetics / Q000502:physiology*; D014867:Water / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D014867:Water; D000040:Abscisic Acid; D042931:Aldehyde Oxidase
keywords: 9-cis-epoxycarotenoid dioxygenase; ABA; AO; Abscisic acid; Anisohydric strategy; CAT; GR; GST; Isohydric strategy; MDA; NCED; Osmotic stress; PEG; POD; SOD; Triticum aestivum; ZEP; abscisic acid; aldehyde oxidase; catalase; glutathione reductase; glutathione transferase; maldondialdehyde; peroxidase; polyethylene glycol; superoxide dismutase; zeaxanthin epoxidase