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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. Environ Toxicol Chem 2013;32:2125-2133. © 2013 SETAC [ABSTRACT FROM AUTHOR]

This study aimed to investigate effects on growth and development and alterations in the nutrient profiles for Arabidopsis thaliana seedlings following uranium exposure. Seventeen-day-old Arabidopsis thaliana seedlings, grown in hydroponics, were exposed to 0, 0.1, 1, 10 and 100 μM uranium for one, three and seven days. Fresh weight of leaves and roots decreased after exposure to 100 μM uranium for one and three days and after exposure to 1, 10 and 100 μM uranium for seven days. Anthocyanous-colored leaves and stunted yellow roots were observed after exposure to 100 μM uranium. The uranium content of the roots highly increased but the root-to-shoot transfer of uranium was limited. Uranium exposure resulted in disturbed macro- and micronutrient profiles, especially following exposure to 100 μM. This study indicates that elevated uranium concentrations can cause important morphological and physiological effects and disturb the nutrient profiles in Arabidopsis thaliana seedlings. [ABSTRACT FROM PUBLISHER]

In soil, high variability of U bioavailability results in large range of apparent U toxic levels for plants. U toxicity on hairy roots of carrot was studied in nutrient gel with a standardized in vitro device. After exposure to 2.5 and 20mgUL−1 for 34 days, U concentration ranged between 4 and 563mgUkg−1 fresh weight which was in good accordance with U accumulation by roots of plant from contaminated soils. Threshold of U toxicity for root length decreased with time and a transient hormesis occurred for exposure to 2.5 and 5mgUL−1. After 34 days and with root length as endpoint, significant toxicity appeared at a gel contamination level above 7.5mgUL−1 corresponding to a maximum U concentration in the liquid phase of 0.8mgL−1. The calculated EC50 for root length as a function of gel contamination was 9.4mgUL−1. Lower threshold and EC50 were observed for biomass as endpoint (resp. 5 and 7.3mgUL−1). The low values observed in this study could result from high sensitivity of carrot to U, high bioavailability of U in gel or absence of interferences with microorganisms. This in vitro device appeared adapted to study toxicity of U to plant roots in optimal conditions of both exposure and observations and is recommended to examine further physiological processes and the influence of microorganism interactions. [Copyright &y& Elsevier]

• Rice plants can recover from gamma irradiation by establishing a new homeostasis. • Leaf age can influence the responses elicited following irradiation and recovery. • Signaling to non-exposed plant tissues establishes a systemic acquired acclimation. Most plant studies on the effects of ionizing radiation at the individual level mainly focus on the immediate responses and not on the responses elicited following recovery. Therefore, we investigated the effects of gamma radiation in rice seedlings exposed to four different gamma dose rates for 2 weeks, after which half of the plants were harvested immediately and the other half were allowed to recover for another 2 weeks. For plants that were harvested immediately, leaf 4 was sampled because it emerged during irradiation, whereas in recovery plants, leaf 4 was sampled as a follow-up as well as leaf 7, which emerged during the recovery period. Plant growth, the antioxidative potential, lignin content and the expression profiles of the rice gene Systemic Acquired Deficient 1 (OsSARD1) and of genes related to DNA repair/replication were analyzed. Overall, the responses elicited in leaf 4 of irradiated and recovery plants indicated that this leaf recovered from exposure via the establishment of a new homeostasis. Conversely, radiation-induced responses appeared in leaf 7 of recovery plants even though it was not directly exposed. Therefore, we hypothesize that a signaling mechanism comes into play to establish this radiation-induced signature, otherwise referred to as systemic acquired acclimation. [ABSTRACT FROM AUTHOR]