Effects of pH on uranium uptake and oxidative stress responses induced in Arabidopsis thaliana

Uranium (U) causes oxidative stress in Arabidopsis thaliana plants grown at pH 5.5. However, U speciation and as such its toxicity strongly depends on environmental parameters, e.g. 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 aimed to analyze U uptake and oxidative stress related responses in Arabidopsis thaliana (Columbia ecotype) under contrasted U chemical speciation conditions. Eighteen‐day‐old seedlings were exposed for 3 days 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 in 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 towards an important role for glutathione in the root defense system against U either by chelation or antioxidative defense mechanisms. In leaves, antioxidative defense mechanisms were activated upon U exposure, indicated by an increased superoxide dismutase and catalase activity. As it seems that U toxicity is influenced by the pH, it is important to consider site‐specific characteristics when making U risk assessments. Environ Toxicol Chem © 2013 SETAC