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Previous studies have found indications that exposure to ionising radiation (IR) results in DNA methylation changes in plants. However, this phenomenon is yet to be studied across multiple generations. Furthermore, the exact role of these changes in the IR-induced plant response is still far from understood. Here, we study the effect of gamma radiation on DNA methylation and its effect across generations in young Arabidopsis plants. A multigenerational set-up was used in which three generations (Parent, generation 1, and generation 2) of 7-day old Arabidopsis thaliana plants were exposed to either of the different radiation treatments (30, 60, 110, or 430 mGy/h) or to natural background radiation (control condition) for 14 days. The parental generation consisted of previously non-exposed plants, whereas generation 1 and generation 2 plants had already received a similar irradiation in the previous one or two generations, respectively. Directly after exposure the entire methylomes were analysed with UPLC-MS/MS to measure whole genome methylation levels. Whole genome bisulfite sequencing was used to identify differentially methylated regions (DMRs), including their methylation context in the three generations and this for three different radiation conditions (control, 30 mGy/h, and 110 mGy/h). Both intra- and intergenerational comparisons of the genes and transposable elements associated with the DMRs were made. Taking the methylation context into account, the highest number of changes were found for cytosines followed directly by guanine (CG methylation), whereas only limited changes in CHG methylation occurred and no changes in CHH methylation were observed. A clear increase in IR-induced DMRs was seen over the three generations that were exposed to the lowest dose rate, where generation 2 had a markedly higher number of DMRs than the previous two generations (Parent and generation 1). Counterintuitively, we did not see significant differences in the plants exposed to the highest dose rate. A large number of DMRs associated with transposable elements were found, the majority of them being hypermethylated, likely leading to more genetic stability. Next to that, a significant number of DMRs were associated with genes (either in their promoter-associated region or gene body). A functional analysis of these genes showed an enrichment for genes related to development as well as various stress responses, including DNA repair, RNA splicing, and (a)biotic stress responses. These observations indicate a role of DNA methylation in the regulation of these genes in response to IR exposure and shows a possible role for epigenetics in plant adaptation to IR over multiple generations. [ABSTRACT FROM AUTHOR]

This study aimed to compare the potential of Lemna minor, Spirodela sp., Eichhornia crassipes and Pistia stratiotes to remove 60Co from a realistic aquatic environment. Although all four plant species performed similarly well after 3 days of exposure to 50 kBq L−1 60Co, Lemna minor and Spirodela sp. came forward as having higher 60Co removal potential. This conclusion is, in first instance, based on the high 60Co removal percentage obtained after a short contact time (e.g. more than 95% could be removed after 6 h by Spirodela sp.). Additionally, Lemna minor and Spirodela sp. accumulated a high amount of 60Co per gram of biomass. For example, Lemna minor accumulated over three times more 60Co per gram of biomass compared to Pistia stratiotes and Eichhornia crassipes. Both plants also performed well in the pH range 5-9. We used Lemna minor to test the influence of the initial 60Co concentration (10, 50, 100 and 200 kBq L−1 60Co) on its phytoremediation capacity but no differences could be observed in removal percentage. In addition, it was shown that by optimising the initial amount of biomass, radioactive waste production can be minimised whilst maintaining high 60Co removal rates. Our study shows that these aquatic plants can be used for phytoremediation of 60Co from contaminated water and can be considered as a “green” addition or alternative for conventional remediation techniques. [ABSTRACT FROM AUTHOR]

In the following study, dose dependent effects on growth and oxidative stress induced by β-radiation were examined to gain better insights in the mode of action of β-radiation induced stress in plant species. Radiostrontium (90Sr) was used to test for β-radiation induced responses in the freshwater macrophyte Lemna minor. The accumulation pattern of 90Sr was examined for L. minor root and fronds separately over a seven-day time period and was subsequently used in a dynamic dosimetric model to calculate β-radiation dose rates. Exposing L. minor plants for seven days to a 90Sr activity concentration of 25 up to 25,000 kBq·L-1 resulted in a dose rate between 0.084 ± 0.004 and 97 ± 8 mGy·h-1. After seven days of exposure, root fresh weight showed a dose dependent decrease starting from a dose rate of 9.4 ± 0.5 mGy·h-1. Based on these data, an EDR10 value of 1.5 ± 0.4 mGy·h-1 was estimated for root fresh weight and 52 ± 17 mGy·h-1 for frond fresh weight. Different antioxidative enzymes and metabolites were further examined to analyze if β-radiation induces oxidative stress in L. minor. [ABSTRACT FROM AUTHOR]

To evaluate the environmental impact of uranium (U) contamination, it is important to investigate the effects of U at ecologically relevant conditions. Since U speciation, and hence its toxicity, strongly depends on environmental pH, the present study aimed to investigate dose-dependent effects of U at pH 7.5. Arabidopsis thaliana plants (Mouse-ear Cress) were exposed for three days to different U concentrations at pH 7.5. In the roots, the increased capacities of ascorbate peroxidase and glutathione reductase indicate an important role for the ascorbate-glutathione cycle during U-induced stress. However, a significant decrease in the ascorbate redox state was observed after exposure to 75 and 100 µM U, indicating that those roots are severely stressed. In accordance with the roots, the ascorbate-glutathione cycle plays an important role in the antioxidative defence systems in A. thaliana leaves exposed to U at pH 7.5 as the ascorbate and glutathione biosynthesis were upregulated. In addition, small inductions of enzymes of the antioxidative defence system were observed at lower U concentrations to counteract the U-induced stress. However, at higher U concentrations it seems that the antioxidative defence system of the leaves collapses as reductions in enzyme activities and gene expression levels were observed. [ABSTRACT FROM AUTHOR]

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]

Abstract: The extent of radiocaesium retention in soil is important to quantify the risk of further foodchain contamination. The Radiocaesium Interception Potential (RIP –, Nature 335, 247–249) is an intrinsic soil parameter which can be used to categorize soils or minerals in terms of their capacity to selectively adsorb radiocaesium. In this study, we measured RIP for a large soil collection (88 soil samples) representative of major FAO soil reference groups on a worldwide scale and tested the possibility to predict the RIP on the basis of other easily accessible or measurable soil data. We also compared RIP values with those obtained from separate chemical extraction experiments. The range of measured RIP values (1.8–13300 mmol kg−1) was shown to include nearly all possible cases of agricultural soil contamination. Only Podzols, Andosols and Ferralsols were clearly characterized by a very low RIP (<2000 mmol kg−1). On a worldwide scale, RIP was in fact slightly related to soil reference type or other simple major physicochemical parameters such as clay percentage or organic matter. Conversely our results indicated a link between the RIP and radiocaesium extractability across very different soils. We showed that, with the proposed scale of RIP values, a simple acid extraction method can provide an operational result highly predictive of potential RIP despite very contrasting soil properties. The RIP could be estimated from the empirical equation: RIP = (−31.701 ∗ log(AER) + 58.886)2 where AER is the fraction of acid-extractable radiocaesium. [Copyright &y& Elsevier]

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]

Subterranean clover inoculated or not with the arbuscular mycorrhizal (AM) fungus Glomus intraradices was grown on soil containing six levels of 238U in the range 0–87 mg kg-1. Increasing U concentration in soil enhanced the U concentration in roots and shoots of both mycorrhizal and nonmycorrhizal plants but had no significant effects on plant dry matter production or root AM colonization. Mycorrhizas increased the shoot dry matter and P concentration in roots and shoots, while in most cases, it decreased the Ca, Mg and K concentrations in plants. The AM fungus influenced U concentration in plants only in the treatment receiving 87 mg U kg-1 soil. In this case, U concentration in shoots of nonmycorrhizal plants was 1.7 times that of shoots of mycorrhizal plants. These results suggested that mycorrhizal fungi can limit U accumulation by plants exposed to high levels of U in soil. [Copyright &y& Elsevier]

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]

The mutants Atnoa1 and Atnia1nia2noa1-2 having a defective chloroplast developmental process, showed enhanced chlorophyll levels when they were grown on Murashige and Skoog (MS) medium and on exposure with uranium (U) on Hoagland medium. Thus we hypothesized that these mutants probably produced NO in MS medium and on exposure with U. Wild-type Col-0, Atnoa1 , Atnia1nia2noa1-2 plants were cultured on modified Hoagland and 1/10 MS media and NO generation in the roots of these mutants was monitored using NO selective fluorescent dyes, DAF-2DA and Fl2E. Both Atnoa1 and Atnia1nia2noa1-2 triple mutants produced NO as observed by increases in DAF-2T and Fl2E fluorescence when these mutants were grown on MS medium but not on Hoagland medium. In presence of NO scavenger, methylene blue (MB, 200 μM), DAF-2T and Fl2E fluorescence was completely abolished. On the other hand treatment of the plants with 25 μM U triggered NO generation. U-treated Atnoa1 and Atnia1nia2noa1-2 plants upregulated genes (POR B, POR D, CHL D) involved in the chlorophyll biosynthesis. From these results it was concluded that Atnoa1 and Atnia1nia2noa1-2 are conditional NO producers and it appears that NO generation in plants substantially depends on growth medium and NIA1, NIA2 or NOA1 does not appear to be really involved in NO generation in MS medium or after U exposure. • Alleged NO-suppressed mutants (Atnoa1 and Atnia1,2noa1-2) exhibit pale phenotype. • Atnoa1 and Atnia1,2noa1-2 exhibited greening in their leaves on MS growth medium. • Atnoa1 and Atnia1,2noa1-2 produced NO on MS growth medium. • Atnoa1 and Atnia1,2noa1-2 produced NO on U exposure in Hoagland medium. [ABSTRACT FROM AUTHOR]

• 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]

Ecotoxicological research provides knowledge on ionising radiation-induced responses in different plant species. However, the sparse data currently available are mainly extracted from acute exposure treatments. To provide a better understanding of environmental exposure scenarios, the response to stress in plants must be followed in more natural relevant chronic conditions. We previously showed morphological and biochemical responses in Lemna minor plants continuously exposed for 7 days in a dose-rate dependent manner. In this study responses on molecular (gene expression) and physiological (photosynthetic) level are evaluated in L. minor plants exposed to ionising radiation. To enable this, we examined the gene expression profiles of irradiated L. minor plants by using an RNA-seq approach. The gene expression data reveal indications that L. minor plants exposed at lower dose rates, can tolerate the exposure by triggering acclimation responses. In contrast, at the highest dose rate tested, a high number of genes related to antioxidative defense systems, DNA repair and cell cycle were differentially expressed suggesting that only high dose rates of ionising radiation drive L. minor plants into survival strategies. Notably, the photosynthetic process seems to be unaffected in L. minor plants among the tested dose rates. This study, supported by our earlier work, clearly indicates that plants shift from acclimation responses towards survival responses at increasing dose rates of ionising radiation. [ABSTRACT FROM AUTHOR]

A Pinus sylvestris stand located in Mol, Belgium was studied for its content of six elements: Ca, K, Mg, Al, Cl and Mn. A fractionation of tree components was carried out into 8 classes (heart and sapwood, inner and outer bark, living branches, twigs and young/old needles) and their element contents were measured. Comparisons were made between the different compartments in terms of absolute and relative element contents. Quantitatively, Ca and K are the main elements: in young needles, Ca + K reach 83% of the elements’ whole stock. The wood compartments (heartwood + sapwood) have generally low element content, as does the outer bark except for Ca (which is bound to suberin) and Al, possibly from atmospheric clay deposition. The inner bark, twigs and needles have high element contents possibly linked to high symplasmic content. The Inner bark shows high Ca and K contents as these elements are involved in phloem transport. Positive correlations were found between Ca and Al, Mn and Cl, K and Cl and K and Mn, attributed to similarity in chemical and biological function. A simple empirical compartment model was developed to derive numerically the transfer rates that reproduce the element distribution within tree compartments. The calculated mass flows appear to be within range of the limited data available from other pine tree studies. This study highlights the potential for coupling of specific elements (including radionuclides) to Ca, K, Mg, Al, Cl and Mn in context of vegetation modelling, by assuming that these elements follow the same pathways. We found indication that 36 Cl, 90 Sr and 137 Cs (environmentally important from the perspective of nuclear power and waste management) can be coupled to Cl, Ca and K fluxes within the tree, increasing the understanding of the cycling of radionuclides in a forest ecosystem. [ABSTRACT FROM AUTHOR]

Uranium (U) is a nonessential and toxic heavy metal and radioactive element. Nitric oxide (NO) and hydrogen peroxide (H 2 O 2 ) are intimately involved in the growth, development and metabolic function of plant cells. In addition to possible toxic activities, a role for these signalling molecules in the regulation of plant responses to toxic metals has been proposed. Here, we investigated the synthesis of NO and H 2 O 2 in Arabidopsis thaliana seedlings exposed to 25 μM U. We demonstrated that U induces NO and H 2 O 2 production in the roots and leaves. Addition of the NO releasing compound, sodium nitroprusside (SNP) as well as the NO synthase inhibitor (L-NAME) to the plants, resulted in a decrease of the U-induced NO production and both alleviated U toxicity as indicated by plant growth (leaf area and biomass). Treatment with L-NAME further resulted in the disappearance of the U-induced H 2 O 2 in the shoots of the plants. It appears that generation of NO and H 2 O 2 is intimately linked in the toxicity response of U-exposed A. thaliana plants. [ABSTRACT FROM AUTHOR]

The high variability of the soil-to-plant transfer factor of radiocaesium (RCs) compels a detailed analysis of the radiocaesium interception potential (RIP) of soil, which is one of the specific factors ruling the RCs transfer. The range of the RIP values for agricultural soils in the Fukushima accident affected area has not yet been fully surveyed. Here, the RIP and other major soil chemical properties were characterised for 51 representative topsoils collected in the vicinity of the Fukushima contaminated area. The RIP ranged a factor of 50 among the soils and RIP values were lower for Andosols compared to other soils, suggesting a role of soil mineralogy. Correlation analysis revealed that the RIP was most strongly and negatively correlated to soil organic matter content and oxalate extractable aluminium. The RIP correlated weakly but positively to soil clay content. The slope of the correlation between RIP and clay content showed that the RIP per unit clay was only 4.8 mmol g − 1 clay, about threefold lower than that for clays of European soils, suggesting more amorphous minerals and less micaceous minerals in the clay fraction of Japanese soils. The negative correlation between RIP and soil organic matter may indicate that organic matter can mask highly selective sorption sites to RCs. Multiple regression analysis with soil organic matter and cation exchange capacity explained the soil RIP ( R 2 = 0.64), allowing us to map soil RIP based on existing soil map information. [ABSTRACT FROM AUTHOR]

The biosphere is constantly exposed to ionising radiation, due to cosmic radiation and the presence of natural and anthropogenic radionuclides in the environment. The biological effects of the resulting radiation exposure are currently poorly understood in plants, due to a large influence of parameters such as species, cultivar, experimental setup and plant age on the response. In this study, 7-, 10- and 14-day - old Arabidopsis thaliana seedlings were exposed to 96 h and 168 h of 100 mGy h −1 chronic γ-radiation in a hydroponic setup. The response of growth, photosynthesis and the transcription of genes involved in DNA repair, cell cycle and signalling were measured. The results show that there is a difference in growth response between plants of different ages and decreasing radiosensitivity with increasing seedling age. This is linked to differences in regulation of DNA repair and cell cycle control at the transcriptional level. [ABSTRACT FROM AUTHOR]

To study the impact of environmental uranium (U) contamination, effects should be analysed at different environmentally relevant pH levels as the speciation of U, and hence its toxicity, is strongly dependent on the pH. As photosynthesis is a major energy producing process in plants intimately connected to plant growth and known to be susceptible to metal stress, the effects of different U concentrations on photosynthesis in 18-day-old Arabidopsis thaliana (Columbia ecotype) are investigated at two contrasting pH levels, pH 4.5 and pH 7.5. At pH 4.5, U is highly taken up by the roots but is poorly translocated to the shoots, while at pH 7.5, less U is taken up but the translocation is higher. The lower U concentrations in the shoots at pH 4.5 are accompanied by a more reduced leaf growth as compared to pH 7.5. In addition, U does not influence the photosynthetic machinery at pH 7.5, while an optimization of the photosynthesis takes place after U exposure at pH 4.5. As such, more of the absorbed quanta are effectively used for photosynthesis accompanied by a decreased non-photochemical quenching and an increased electron transport rate. Since the enhanced photosynthesis at pH 4.5 is accompanied by a decreased growth, we suggest that the energy produced during photosynthesis is used for defence reactions against U-induced oxidative stress rather than for growth. As such, a high discrepancy was observed between the two pH levels, with an optimized photosynthetic apparatus at pH 4.5 and almost no effects at pH 7.5. [ABSTRACT FROM AUTHOR]

Highlights: [•] Uranium is highly taken up by roots but concentrations in leaves remain low. [•] Increase efficiency of photosystem II under uranium stress. [•] Decrease non-photochemical quenching under uranium stress. [•] Increase in photosynthetic rate in the light-limited region of rapid light curve. [Copyright &y& Elsevier]

Abstract: Arabidopsis thaliana was exposed to low-dose chronic gamma irradiation during a full life cycle (seed to seed) and several biological responses were investigated. Applied dose rates were 2336, 367 and 81 μGy h−1. Following 24 days (inflorescence emergence), 34 days (∼50% of flowers open) and 54 days (silice ripening) exposure, plants were harvested and monitored for biometric parameters, capacities of enzymes involved in the antioxidative defence mechanisms (SOD, APOD, GLUR, GPOD, SPOD, CAT, ME), glutathione and ascorbate pool, lipid peroxidation products, altered gene expression of selected genes encoding for antioxidative enzymes or reactive oxygen species production, and DNA integrity. Root fresh weight was significantly reduced after gamma exposure compared to the control at all stages monitored but no significant differences in root weight for the different dose rates applied was observed. Leaf and stem fresh weight were significantly reduced at the highest irradiation level after 54 days exposure only. Also total plant fresh was significantly lower at silice riping and this for the highest and medium dose rate applied. The dose rate estimated to result in a 10% reduction in growth (EDR-10) ranged between 60 and 80 μGy h−1. Germination of seeds from the gamma irradiated plants was not hampered. For several of the antioxidative defence enzymes studied, the enzyme capacity was generally stimulated towards flowering but generally no significant effect of dose rate on enzyme capacity was observed. Gene analysis revealed a significant transient and dose dependent change in expression of RBOHC indicating active reactive oxygen production induced by gamma irradiation. No effect of irradiation was observed on concentration or reduction state of the non-enzymatic antioxidants, ascorbate and glutathione. The level of lipid peroxidation products remained constant throughout the observation period and was not affected by dose rate. The comet assay did not reveal any effect of gamma dose rate on DNA integrity. [Copyright &y& Elsevier]

Abstract: Plantings of Scots pine (Pinus sylvestris L.) on a waste burial site in the Chernobyl Red Forest was shown to greatly influence the long term redistribution of radioactivity contained in sub-surfaces trenches. After 15 years of growth, aboveground biomass of the average tree growing on waste trench no.22 had accumulated 1.7 times more 137Cs than that of trees growing off the trench, and 5.4 times more 90Sr. At the scale of the trench and according to an average tree density of 3300 trees/ha for the study zone, tree contamination would correspond to 0.024% of the 137Cs and 2.52% of the 90Sr contained in the buried waste material. A quantitative description of the radionuclide cycling showed a potential for trees to annually extract up to 0.82% of the 90Sr pool in the trench and 0.0038% of the 137Cs. A preferential 90Sr uptake from the deep soil is envisioned while pine roots would take up 137Cs mostly from less contaminated shallow soil layers. The current upward flux of 90Sr through vegetation appeared at least equal to downward loss in waste material leaching as reported by Dewiere et al. (2004, Journal of Environmental Radioactivity 74, 139–150). Using a prospective calculation model, we estimated that maximum 90Sr cycling can be expected to occur at 40 years post-planting, resulting in 12% of the current 90Sr content in the trench transferred to surface soils through biomass turnover and 7% stored in tree biomass. These results are preliminary, although based on accurate methodology. A more integrated ecosystem study leading to the coupling between biological and geochemical models of radionuclide cycling within the Red Forest seems opportune. Such a study would help in the adequate management of that new forest and the waste trenches upon which they reside. [Copyright &y& Elsevier]

Abstract: The production of reactive oxygen species (ROS) and the induction of the antioxidative defense mechanism are very important in heavy metal toxicity. In this study, biological effects induced after uranium contamination were investigated for Arabidopsis thaliana. Three-week-old seedlings were exposed for 4days to 100μM U in an adjusted Hoagland solution. Uranium exposure caused a decreased growth of leaves (38%) and roots (70%) and a modified nutrient profile was observed. Investigation of lipid peroxidation products indicated a significant increase of membrane damage. Important ROS-producing and -scavenging enzymes were studied at transcriptional and protein level to investigate the importance of the ROS-signature in uranium toxicity. Elevated gene expression was observed for NADPH-oxidase, a ROS-producing enzyme. Changes in gene expression for different ROS-scavenging enzymes as Cu/ZnSOD, FeSOD and APX were also observed. Analysis of enzyme capacities showed little effects after uranium contamination. Higher ascorbate levels in uranium exposed leaves suggested an increase of antioxidative defense via the ascorbate-glutathione pathway after uranium exposure. Theoretical calculations indicated rapid formation of uranium-phosphate precipitates if normal phosphate concentrations are used. Precipitation tests recommend the use of 25μM P in combination with 100μM U to inhibit uranium precipitation. Because this combination was used for uranium toxicity investigation, the influence of this low phosphate concentration on plant growth and oxidative stress had to be evaluated. Minor differences between low phosphate (25μM P) and high phosphate (100μM P) treatments were observed justifying the use of the low phosphate concentration in combination with uranium. [Copyright &y& Elsevier]