title: Nitric oxide retards xanthine oxidase-mediated superoxide anion generation in Phalaenopsis flower: an implication of NO in the senescence and oxidative stress regulation.
abstract: Senescence is a developmentally regulated and highly ordered sequence of events. Senescence leads to abscission of plant organs and eventually leads to death of a plant or part of it. Present study revealed that Phalaenopsis flower undergo senescence due to over activation of O(2) (.-)generating xanthine oxidase (XO), which consequently increases the concentrations of O(2) (.-) leading to enhanced oxidative damage and disturbed cellular redox environment as indicated by increased lipid peroxidation and DHA/AsA + DHA ratio, respectively. While activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and non-specific peroxidase (POD) were enhanced in sepals and petals of old flower, activities of catalase (CAT) and glutathione reductase (GR) were decreased. Exogenous application of nitric oxide (NO) retarded H(2)O(2)-induced senescence of Phalaenopsis flower by downregulating activity of XO and concentrations of O(2) (.-), H(2)O(2) and malondialdehyde (MDA, an index of lipid peroxidation). Exogenous application of NO also downregulated SOD activity and upregulated antioxidant enzymes involved in the detoxification of H(2)O(2) (CAT and APX), and in the regulation of redox couples viz, monodehydroascorbate reductase (MDHAR) and GR, together with the modulation in non-protein thiol status and DHA/AsA + DHA ratio.
authors.affiliation: Research Center for the Development of Advanced Horticultural Technology, Chungbuk National University, Cheongju, Republic of Korea. rktewari_bot@yahoo.com
authors.forename: Rajesh Kumar
authors.initials: RK
authors.lastname: Tewari
authors.forename: Praveen
authors.initials: P
authors.lastname: Kumar
authors.forename: Soohyun
authors.initials: S
authors.lastname: Kim
authors.forename: Eun-Joo
authors.initials: EJ
authors.lastname: Hahn
authors.forename: Kee-Yoeup
authors.initials: KY
authors.lastname: Paek
mesh_terms: D016922:Cellular Senescence / Q000187:drug effects; D035264:Flowers / Q000187:drug effects* / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D009569:Nitric Oxide / Q000494:pharmacology*; D029595:Orchidaceae / Q000187:drug effects* / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects; D013481:Superoxides / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000378:metabolism*
chemical_list: D013481:Superoxides; D009569:Nitric Oxide; D014969:Xanthine Oxidase