title: Elevated ROS-scavenging enzymes contribute to acclimation to UV-B exposure in transplastomic tobacco plants, reducing the role of plastid peroxidases.
abstract: Leaf peroxidases play a key role in the successful acclimation of plants to low UV-B doses. The aim of the present study was to examine whether selective enhancement of alternative chloroplast antioxidant pathways achieved by chloroplast transformation affected the need for peroxidase defense. Transplastomic tobacco lines expressing glutathione reductase in combination with either dehydroascorbate reductase or glutathione-S-transferase in their plastids exhibited better tolerance to supplemental UV-B than wild type plants. After 10days UV treatment, both the maximum and effective quantum yields of PSII decreased in the wild type by 10% but were unaffected in either of the transformed lines. Activities of total peroxidase and ascorbate peroxidase, in addition to dehydroascorbate reductase and gluthatione-S-transferase, were increased by UV in all lines. Gluthatione reductase activity was unaffected by UV in the transplastomic line engineered to have a higher constitutive level of this enzyme, but increased in the two other genotypes. However, the observed more successful acclimation required less activation of peroxidases in the doubly transformed plants than in the wild type and less increase in non-enzymatic hydroxyl radical neutralization in the dehydroascorbate reductase plus glutathione reductase fortified plants than in either of the other lines. These results highlight the fundamental role of efficient glutathione, and especially ascorbate, recycling in the chloroplast in response to exposure of plants to UV-B. They also identify chloroplast localized peroxidases among the large variety of leaf peroxidases as essential elements of defense, supporting our earlier hypothesis on hydrogen peroxide UV-B photo-cleavage as the primary mechanism behind damage.
authors.affiliation: Department of Plant Biology, Faculty of Sciences, University of Pécs, Pécs, Hungary.
authors.forename: Gyula
authors.initials: G
authors.lastname: Czégény
authors.affiliation: Biology Department, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland.
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Le Martret
authors.affiliation: Department of Plant Biology, Faculty of Sciences, University of Pécs, Pécs, Hungary.
authors.forename: Dóra
authors.initials: D
authors.lastname: Pávkovics
authors.affiliation: Biology Department, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Dix
authors.affiliation: Department of Plant Biology, Faculty of Sciences, University of Pécs, Pécs, Hungary. Electronic address: ehideg@gamma.ttk.pte.hu.
authors.forename: Éva
authors.initials: É
authors.lastname: Hideg
mesh_terms: D000064:Acclimatization / Q000528:radiation effects*; D000975:Antioxidants / Q000378:metabolism; D017665:Hydroxyl Radical / Q000378:metabolism; D010544:Peroxidases / Q000378:metabolism*; D010788:Photosynthesis / Q000528:radiation effects; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D030821:Plants, Genetically Modified; D018087:Plastids / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D017665:Hydroxyl Radical; D010544:Peroxidases
keywords: Chloroplast transformant; Dehydroascorbate reductase; Glutathione reductase; Glutathione-S-transferase; Reactive oxygen species; UV radiation