title: Ultraviolet-B- and ozone-induced biochemical changes in antioxidant enzymes of Arabidopsis thaliana.
abstract: Earlier studies with Arabidopsis thaliana exposed to ultraviolet B (UV-B) and ozone (O3) have indicated the differential responses of superoxide dismutase and glutathione reductase. In this study, we have investigated whether A. thaliana genotype Landsberg erecta and its flavonoid-deficient mutant transparent testa (tt5) is capable of metabolizing UV-B- and O3-induced activated oxygen species by invoking similar antioxidant enzymes. UV-B exposure preferentially enhanced guaiacol-peroxidases, ascorbate peroxidase, and peroxidases specific to coniferyl alcohol and modified the substrate affinity of ascorbate peroxidase. O3 exposure enhanced superoxide dismutase, peroxidases, glutathione reductase, and ascorbate peroxidase to a similar degree and modified the substrate affinity of both glutathione reductase and ascorbate peroxidase. Both UV-B and O3 exposure enhanced similar Cu,Zn-superoxide dismutase isoforms. New isoforms of peroxidases and ascorbate peroxidase were synthesized in tt5 plants irradiated with UV-B. UV-B radiation, in contrast to O3, enhanced the activated oxygen species by increasing membrane-localized NADPH-oxidase activity and decreasing catalase activities. These results collectively suggest that (a) UV-B exposure preferentially induces peroxidase-related enzymes, whereas O3 exposure invokes the enzymes of superoxide dismutase/ascorbate-glutathione cycle, and (b) in contrast to O3, UV-B exposure generated activated oxygen species by increasing NADPH-oxidase activity.
authors.affiliation: Department of Horticultural Science, University of Guelph, Ontario, Canada.
authors.forename: M V
authors.initials: MV
authors.lastname: Rao
authors.forename: G
authors.initials: G
authors.lastname: Paliyath
authors.forename: D P
authors.initials: DP
authors.lastname: Ormrod
mesh_terms: D000975:Antioxidants; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000528:radiation effects; D002374:Catalase / Q000032:analysis; D018506:Gene Expression Regulation, Plant; D005980:Glutathione Reductase / Q000032:analysis; D009247:NADH, NADPH Oxidoreductases / Q000032:analysis; D019255:NADPH Oxidases; D010126:Ozone / Q000494:pharmacology*; D010544:Peroxidases / Q000032:analysis; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000032:analysis; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D010126:Ozone; D010544:Peroxidases; D002374:Catalase; D013482:Superoxide Dismutase; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D005980:Glutathione Reductase