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Additional file 16: Figure S5. Cladogram of glutamine synthetase isoform in L. minor (Lminor), S. polyrhiza (Spipo), A. thaliana (AT), O. indica (OSINDICA) and B. distachyon (BD). The phylogentic relationships of glutamine synthetase from different species have been calculated under default parameters using phylogeny.fr.

In the following study, dose dependent effects on growth and oxidative stress induced by -radiation were examined to gain better insights in the mode of action of -radiation induced stress in plant species. Radiostrontium (Sr-90) was used to test for -radiation induced responses in the freshwater macrophyte Lemna minor. The accumulation pattern of Sr-90 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 -radiation dose rates. Exposing L. minor plants for seven days to a Sr-90 activity concentration of 25 up to 25,000 kBqL(-1) resulted in a dose rate between 0.084 +/- 0.004 and 97 +/- 8 mGyh(-1). After seven days of exposure, root fresh weight showed a dose dependent decrease starting from a dose rate of 9.4 +/- 0.5 mGyh(-1). Based on these data, an EDR10 value of 1.5 +/- 0.4 mGyh(-1) was estimated for root fresh weight and 52 +/- 17 mGyh(-1) for frond fresh weight. Different antioxidative enzymes and metabolites were further examined to analyze if -radiation induces oxidative stress in L. minor. The authors thank the Research foundation-Flanders (FWO) (G.A040.11N) and the European Commission Contract Fission-2010-3.5.1-269672 Strategy for Allied Radioecology (www.star-radioecology.org) for financial support of this work. Belgian nuclear research institute (SCK.CEN) is further thanked for funding the PhD of A. Van Hoeck.

When terrestrial environments get contaminated with long-lived gamma emitting radionuclides, plants that grow in these contaminated areas are exposed to gamma radiation during consecutive generations. Therefore it is important to evaluate the gamma induced stress response in plants in and between generations. The objective of this research is to reveal differences at the level of the antioxidative stress response between generations with a different radiation history. An experiment was conducted in which 7-days old Arabidopsis thaliana plants were exposed for 14 days to four different gamma dose rates: 22 mGy/h, 38 mGy/h, 86 mGy/h and 457 mGy/h. Two different plant groups were used: plants that were not exposed to gamma radiation before (P0) and plants that received the aforementioned gamma treatment during their previous generation (S1). Growth, the concentration of the antioxidants ascorbate and glutathione, a number of antioxidative enzyme activities and their gene transcript levels were analysed. A dose-rate dependent induction was seen for catalase (CAT) and guaiacol peroxidase (GPX) in the roots and for syringaldazine peroxidase (SPX) in the shoots. Differences between the two generations were observed for CAT and GPX in the roots, where a significantly higher activity of these reactive oxygen species (ROS) detoxifying enzymes was observed in the S1 generation. For SPX in the shoots, a dose dependent upregulation was observed in the PO generation. However, high SPX activities were present for all doses in the S1 generation. These differences in enzyme activity between generations for SPX and GPX and the involvement of these enzymes in cell wall biosynthesis, suggest an important role for cell wall strengthening in the response to gamma irradiation. (C) 2016 Elsevier Ltd. All rights reserved. This project was supported by the European project COMET (7th PCRD EURATOM Contract Number: Fission-2012-3.4.1-604794) (www.comet-radioecology.org) and the Belgian nuclear research centre (SCK CEN).

Background: Freshwater duckweed, comprising the smallest, fastest growing and simplest macrophytes has various applications in agriculture, phytoremediation and energy production. Lemna minor, the so-called common duckweed, is a model system of these aquatic plants for ecotoxicological bioassays, genetic transformation tools and industrial applications. Given the ecotoxic relevance and high potential for biomass production, whole-genome information of this cosmopolitan duckweed is needed. Results: The 472 Mbp assembly of the L. minor genome (2n = 40; estimated 481 Mbp; 98.1 %) contains 22,382 protein- coding genes and 61.5 % repetitive sequences. The repeat content explains 94.5 % of the genome size difference in comparison with the greater duckweed, Spirodela polyrhiza (2n = 40; 158 Mbp; 19,623 protein-coding genes; and 15.79 % repetitive sequences). Comparison of proteins from other monocot plants, protein ortholog identification, OrthoMCL, suggests 1356 duckweed-specific groups (3367 proteins, 15.0 % total L. minor proteins) and 795 Lemna-specific groups (2897 proteins, 12.9 % total L. minor proteins). Interestingly, proteins involved in biosynthetic processes in response to various stimuli and hydrolase activities are enriched in the Lemna proteome in comparison with the Spirodela proteome. Conclusions: The genome sequence and annotation of L. minor protein-coding genes provide new insights in biological understanding and biomass production applications of Lemna species. The authors thank the Research foundation-Flanders (FWO) (G.A040.11N) and the European Commission Contract Fission-2010-3.5.1-269672 Strategy for Allied Radioecology (http://www.star-radioecology.org) for financial support of this work. Belgian nuclear research institute (SCK.CEN) is further thanked for funding the PhD of AVH. HXC is supported by the German Research Foundation (SCH 951/18 1). The people from CALCUA at the University of Antwerp are acknowledged for assisting high performance computing (http://www.uantwerpen.be/calcua). The authors also thank L. Leus, ILVO, for estimating DNA genome size through flow cytometry.

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 mu M 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. This work was supported by a grant for Eline Saenen from the Belgian Nuclear Research Centre (SCK center dot CEN).