title: Effects of pH on uranium uptake and oxidative stress responses induced in Arabidopsis thaliana.
abstract: Uranium (U) causes oxidative stress in Arabidopsis thaliana plants grown at pH 5.5. However, U speciation and its toxicity strongly depend on environmental parameters, for example pH. It is unknown how different U species determine U uptake and translocation within plants and how they might affect the oxidative defense mechanisms of these plants. The present study analyzed U uptake and oxidative stress-related responses in A. thaliana (Columbia ecotype) under contrasted U chemical speciation conditions. The 18-d-old seedlings were exposed for 3 d to 25 µM U in a nutrient solution of which the pH was adjusted to 4.5, 5.5, 6.5, or 7.5. Results indicate that there is a different rate of U uptake and translocation at the different pHs, with high uptake and low translocation at low pH and lower uptake but higher translocation at high pH. After U exposure, an increased glutathione reductase activity and total glutathione concentration were observed in U-exposed roots, pointing toward an important role for glutathione in the root defense system against U either by chelation or by antioxidative defense mechanisms. In leaves, antioxidative defense mechanisms were activated on U exposure, indicated by increased superoxide dismutase and catalase activity. As it seems that U toxicity is influenced by pH, it is important to consider site-specific characteristics when making U risk assessments.
authors.affiliation: Belgian Nuclear Research Centre, Biosphere Impact Studies, Mol, Belgium. eline.saenen@sckcen.be
authors.forename: Eline
authors.initials: E
authors.lastname: Saenen
authors.forename: Nele
authors.initials: N
authors.lastname: Horemans
authors.forename: Nathalie
authors.initials: N
authors.lastname: Vanhoudt
authors.forename: Hildegarde
authors.initials: H
authors.lastname: Vandenhove
authors.forename: Geert
authors.initials: G
authors.lastname: Biermans
authors.forename: May
authors.initials: M
authors.lastname: Van Hees
authors.forename: Jean
authors.initials: J
authors.lastname: Wannijn
authors.forename: Jaco
authors.initials: J
authors.lastname: Vangronsveld
authors.forename: Ann
authors.initials: A
authors.lastname: Cuypers
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects* / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D018384:Oxidative Stress / Q000187:drug effects*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D014501:Uranium / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D000975:Antioxidants; D014501:Uranium; D013482:Superoxide Dismutase; D005978:Glutathione
keywords: Arabidopsis thaliana; Oxidative stress; Uranium; pH