Belgian Nuclear Research Centre, Biosphere Impact Studies, Mol, Belgium.
Environ Toxicol Chem. 2013 Sep;32(9):2125-33. doi: 10.1002/etc.2290.
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.
在 pH 值为 5.5 的条件下，铀（U）会导致拟南芥植物产生氧化应激。然而，U 的形态及其毒性强烈依赖于环境参数，例如 pH 值。目前尚不清楚不同的 U 物种如何决定 U 在植物体内的吸收和转运，以及它们如何影响这些植物的氧化防御机制。本研究分析了在对照 U 化学形态条件下，不同 pH 值对拟南芥（哥伦比亚生态型）U 吸收和与氧化应激相关反应的影响。18 天龄的幼苗在 pH 值分别为 4.5、5.5、6.5 和 7.5 的营养液中暴露 3 天，营养液中含有 25 μM U。结果表明，在不同 pH 值下，U 的吸收和转运速率不同，在低 pH 值下吸收速率高但转运速率低，而在高 pH 值下吸收速率低但转运速率高。U 暴露后，U 暴露的根中谷胱甘肽还原酶活性和总谷胱甘肽浓度增加，表明谷胱甘肽在根防御系统中通过螯合或抗氧化防御机制对抗 U 可能发挥重要作用。在叶片中，U 暴露会激活抗氧化防御机制，表现为超氧化物歧化酶和过氧化氢酶活性增加。由于 U 的毒性似乎受到 pH 值的影响，因此在进行 U 风险评估时，考虑特定地点的特征非常重要。
