title: Cytokinin oxidase/dehydrogenase overexpression modifies antioxidant defense against heat, drought and their combination in Nicotiana tabacum plants.
abstract: Cytokinins (CKs) as well as the antioxidant enzyme system (AES) play important roles in plant stress responses. The expression and activity of antioxidant enzymes (AE) were determined in drought, heat and combination of both stresses, comparing the response of tobacco plants overexpressing the main cytokinin degrading enzyme, cytokinin oxidase/dehydrogenase, under the control of root-specific WRKY6 promoter (W6:CKX1 plants) or constitutive promoter (35S:CKX1 plants) and the corresponding wild-type (WT). Expression levels as well as activities of cytosolic ascorbate peroxidase, catalase 3, and cytosolic superoxide dismutase were low under optimal conditions and increased after heat and combined stress in all genotypes. Unlike catalase 3, two other peroxisomal enzymes, catalase 1 and catalase 2, were transcribed extensively under control conditions. Heat stress, in contrast to drought or combined stress, increased catalase 1 and reduced catalase 2 expression in WT and W6:CKX1 plants. In 35S:CKX1, catalase 1 expression was enhanced by heat or drought, but not under combined stress conditions. Mitochondrial superoxide dismutase expression was generally higher in 35S:CKX1 plants than in WT. Genes encoding for chloroplastic AEs, stromatal ascorbate peroxidase, thylakoidal ascorbate peroxidase and chloroplastic superoxide dismutase, were strongly transcribed under control conditions. All stresses down-regulated their expression in WT and W6:CKX1, whereas more stress-tolerant 35S:CKX1 plants maintained high expression during drought and heat. The achieved data show that the effect of down-regulation of CK levels on AES may be mediated by altered habit, resulting in improved stress tolerance, which is associated with diminished stress impact on photosynthesis, and changes in source/sink relations.
authors.affiliation: Institute of Experimental Botany AS CR, Rozvojová 263, 16502 Prague 6, Czech Republic; Department of Experimental Plant Biology, Faculty of Science, Charles University in Prague, Viničná 5, 128 44 Prague 2, Czech Republic. Electronic address: Lubovska@ueb.cas.cz.
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Lubovská
authors.affiliation: Institute of Experimental Botany AS CR, Rozvojová 263, 16502 Prague 6, Czech Republic. Electronic address: JanaDobra@centrum.cz.
authors.forename: Jana
authors.initials: J
authors.lastname: Dobrá
authors.affiliation: Institute of Experimental Botany AS CR, Rozvojová 263, 16502 Prague 6, Czech Republic. Electronic address: storchova@ueb.cas.cz.
authors.forename: Helena
authors.initials: H
authors.lastname: Storchová
authors.affiliation: Institute of Experimental Botany AS CR, Rozvojová 263, 16502 Prague 6, Czech Republic. Electronic address: wilhelmova@ueb.cas.cz.
authors.forename: Naďa
authors.initials: N
authors.lastname: Wilhelmová
authors.affiliation: Institute of Experimental Botany AS CR, Rozvojová 263, 16502 Prague 6, Czech Republic. Electronic address: vankova@ueb.cas.cz.
authors.forename: Radomíra
authors.initials: R
authors.lastname: Vanková
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D060387:Ascorbate Peroxidases / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism; D015536:Down-Regulation; D055864:Droughts; D018506:Gene Expression Regulation, Plant; D006358:Hot Temperature; D008954:Models, Biological; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D013312:Stress, Physiological; D013482:Superoxide Dismutase / Q000378:metabolism; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics / Q000502:physiology
chemical_list: D000975:Antioxidants; D029681:Arabidopsis Proteins; D003583:Cytokinins; D010088:Oxidoreductases; D060387:Ascorbate Peroxidases; D002374:Catalase; D013482:Superoxide Dismutase; C019984:cytokinin oxidase
keywords: Antioxidant enzymes; Cytokinin; Drought; Heat