Robin Nauts

<p>Schemes represent a global gene expression response (A) immediately after irradiation; (B) after 2H and 5H of recovery period. Blue colour, stand for down-regulated genes. Red colour stand for up-regulated genes, Green colour stand for restored expression of the initial silenced genes. (A) The largest changes in transcription occurred upon irradiation, as part of a kind of an “Emergency Response”. Cells displayed a <b>reduced transcription</b> for photosynthesis and energy production (PSII, PSI, ATP), and for carbon and nitrogen metabolism during irradiation. The CO<sub>2</sub> fixation via the Calvin-Benson-Bassham cycle (CBB), glycogen biosynthesis (gluconeogenesis) and the tricarboxylic acid cycle (TCA) were repressed. The transcription of the SigE regulator acting as nitrogen-dependent activator for catabolic genes towards glycogen degradation (glycolysis) was induced. Also a re-routing of the metabolic flux to glycolysis and the pentose phosphate pathway (PPP) was seen. A synthesis of carbon storage molecules (PHA) and compatible solutes (trehalose) was seen. The expression of polyamine import (<i>potBC)</i>, well known as a group of nitrogen-containing C-compounds which help in cell survival during stress, was recorded. The import of nitrate or cyanate as N-sources was repressed (<i>nrtABCD</i>, <i>cynBD</i>). In parallel also the metabolism of agmatine, a known competitive inhibitor of polyamine transport, was repressed. The cellular protection, detoxification, and repair were <b>enhanced</b> immediately after irradiation. In an effort to maintain the intracellular redox balance while provide sufficient metal-cofactors for enzymes, selective metal export (<i>copA)</i> and import (<i>feoAB</i>, <i>cutA</i>, <i>corA</i>, <i>mtgC</i>, <i>cbiQ1</i>, <i>cbiQ2</i>, <i>znuA</i>) was induced. There was upregulation of isiA gene encoding the CP43’ protein, which is an auxiliary antenna complex, to compensate for the loss of phycobilisomes. This protein may also serve as a chlorophyll storage molecule contributing to the reassembly of reaction centres during recovery. In addition, ROS detoxification was activated via the expression of the peroxiredoxine enzyme (<i>ahpC</i>) and the glutathione synthesis genes. The generation of glutathione starts at T0H via the formation of glutamate from proline by <i>hyuA</i>, from aspartate by aspartate aminotransferase <i>(aat1)</i>, from 1-pyrroline-5-carboxylate by (<i>putA</i>), and from 2-oxoglutarate via GLDH (see Fig 8B). Glutamate synthesis via the GS/GOGAT cycle was repressed. The final synthesis of glutathione from glutamate occurred via glutathione (GSH) synthase <i>(gshB)</i>, which continued during recovery (see Fig 8B). Chaperones (<i>dnaK1</i>, <i>dnaK2</i>, <i>hspA</i>, <i>cbpA</i>) and proteases (<i>clpB2</i>) were also significantly induced during this stage, to remove damaged proteins. The free amino-acids released from protein degradation, likely lead to the production of urea, and the urease (<i>ureABC)</i> activity, transforming urea to ammonium, was induced. In parallel <i>Arthrospira</i> enhance some genes related to DNA repair system (<i>uvrBCD</i> for nucleotide excision and repair, <i>ruvB</i> resolving holiday junction, and <i>recJ</i>, <i>dnaG and mod</i> genes). The DNA-repair mechanism of <i>Arthrospira</i> included also enzymatic restriction modification (<i>hsdr</i>) and endonucleases. (B) During the <u><b>later phase</b></u><i>Arthrospira</i> cells try to <u><b>recover from the damage; which lead to a slowly restored expression</b></u> of the genes related to photosynthesis and energy production, carbon fixation via the CBBn cycle and gluconeogenesis, TCA cycle. Expression of the hydrogenase genes (<i>hypA1</i>, <i>hypB1and hoxW</i>). Metal chaperone proteins HypA and HypB are required for the nickel insertion step of [NiFe]-hydrogenase maturation. In parallel slight reactivation of amino-acid transport (<i>aapJPQ</i>, <i>argGHJ</i>, <i>iaaA</i>) occurred. The genes for import of taurine (<i>tauABC</i>) known as organic sulphur and amino source were highly induced. The restoration of agmatinase, the key enzyme of agmatine hydrolysis was seen in recovery period. ROS detoxification was maintained efficiently via the expression for glutathione biosynthesis (GSH). Few genes related to protein damage clean up (proteases and chaperones) and DNA repair maintained their expression during recovery. The expression of gene cluster <i>arhABCDEF</i>, enriched during recovery, was seen.</p

<p>Scatter plot showing the differentially expressed genes of <i>Arthrospira</i> sp. PCC 8005 in response to gamma irradiation plotted accordingly to their change in mRNA concentration (Log<sub>2</sub> fold change values), for 3 radiation doses (800, 1600 and 3200 Gy) and 3 time points after radiation (0 hours, 2 hours, 5 hours).</p

<p>This plot visualises whether a certain gene cluster (1–9, on the vertical axis) is containing a higher number of representatives of a specific COG (21 different COGs, on the horizontal axis) then would be expected by chance. The COG functional category is shown in the vertical direction, the clusters of differentially expressed genes in the horizontal direction. The colour code is according to the <sup>10</sup>log value of the corresponding p-value of the GSEA analysis: a p-value of smaller than 1.10<sup>–4</sup> (<sup>10</sup>log-value of 4) results in a colour code red, a p-value of 1 (<sup>10</sup>log value 0) results in colour code white.</p

The edible cyanobacterium Arthrospira is resistant to ionising radiation. The cellular mecha-nisms underlying this radiation resistance are, however, still largely unknown. Therefore, additional molecular analysis was performed to investigate how these cells can escape from, protect against, or repair the radiation damage. Arthrospira cells were shortly exposed to different doses of 60Co gamma rays and the dynamic response was investigated by moni-toring its gene expression and cell physiology at different time points after irradiation. The results revealed a fast switch from an active growth state to a kind of 'survival modus ' during which the cells put photosynthesis, carbon and nitrogen assimilation on hold and activate pathways for cellular protection, detoxification, and repair. The higher the radiation dose, the more pronounced this global emergency response is expressed. Genes repressed dur-ing early response, suggested a reduction of photosystem II and I activity ...

Abstract: 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

Pollution of surface waters is a worldwide problem for people and wildlife. Remediation and phytoremediation approaches can offer a solution to deal with specific scenarios. Lemna minor, commonly known as duckweed, can absorb and accumulate pollutants in its biomass. To evaluate if L. minor could be applied for phytoremediation purposes, it is necessary to further investigate its remediation capability and to identify which parameters affect the remediation process. Such a model must include both plant growth and pollutant exchange. A remediation model based on a robust experimental study can help to evaluate L. minor as a proper remediation strategy and to predict the outcome of a L. minor based remediation system. To set up this model, this paper focusses on a detailed experimental study and a comprehensive mathematical modelling approach to represent L. minor growth as a function of biomass, temperature, light irradiation and variable nutrient concentrations. The influence of environmental conditions on L. minor growth was studied, by composing 7 days growth curves. Plants were grown under predefined environmental conditions (25°C, 14h photoperiod, 220 μmol m-2 s-1 light intensity and a modified Hoagland solution with 23.94 mg N L-1 and 3.10 mg P L-1 (N:P ratio of 7.73)) as standard for all experiments. The influence of different temperatures (6, 10, 15, 20, 25, 30 and 35°C), light intensities (63, 118, 170, 220 and 262 μmol m-2 s-1), photoperiods (12h and 14h) and N:P ratios (1.18, 3.36, 7.73 and 29.57) were tested in the model. As a result, a growth model was optimised using separate datasets for temperature, light intensity, photoperiod and nutrients and validated by further integrated testing. The growth model is a stable platform for application in phytoremediation of radionuclides in contaminated water, to be extended in future studies with information of pollutant uptake, pollutant-nutrient interactions and transfer to the biomass.

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 youngArabidopsisplants. A multigenerational set-up was used in which three generations (Parent, generation 1, and generation 2) of 7-day oldArabidopsis thalianaplants 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 a...

This study aimed to compare the potential of Lemna minor, Spirodela sp., Eichhornia crassipes and Pistia stratiotes to remove Co from a realistic aquatic environment. Although all four plant species performed similarly well after 3 days of exposure to 50 kBq LCo, Lemna minor and Spirodela sp. came forward as having higher Co removal potential. This conclusion is, in first instance, based on the high Co 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 Co per gram of biomass. For example, Lemna minor accumulated over three times more Co 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 Co concentration (10, 50, 100 and 200 kBq LCo) on its phytoremediation capacity but no differences could be observed in remov...

Common duckweed (Lemna minor L.) is ideally suited to test the impact of metals on freshwater vascular plants. Literature on cadmium (Cd) and uranium (U) oxidative responses in L. minor are sparse or, for U, non-existent. It was hypothesised that both metals impose concentration-dependent oxidative stress and growth retardation on L. minor. Using a standardised 7-day growth inhibition test, the adverse impact of these metals on L. minor growth was confirmed, with EC50 values for Cd and U of 24.1 ± 2.8 and 29.5 ± 1.9 μm, respectively, and EC10 values of 1.5 ± 0.2 and 6.5 ± 0.9 μm, respectively. The metal-induced oxidative stress response was compared through assessing the activity of different antioxidative enzymes [catalase, glutathione reductase, superoxide dismutase (SOD), ascorbate peroxidase (APOD), guaiacol peroxidase (GPOD) and syringaldizyne peroxidase (SPOD)]. Significant changes in almost all antioxidative enzymes indicated their importance in counteracting the U- and Cd-imposed oxidative burden. However, some striking differences were also observed. For activity of APODs and SODs, a biphasic but opposite response at low Cd compared to U concentrations was found. In addition, Cd (0.5-20 μm) strongly enhanced plant GPOD activity, whereas U inhibited it. Finally, in contrast to Cd, U up to 10 μm increased the level of chlorophyll a and b and carotenoids. In conclusion, although U and Cd induce similar growth arrest in L. minor, the U-induced oxidative stress responses, studied here for the first time, differ greatly from those of Cd.

As the environment is inevitably exposed to ionizing radiation from natural and anthropogenic sources, it is important to evaluate gamma radiation induced stress responses in plants. The objective of this research is therefore to investigate radiation effects in Arabidopsis thaliana on individual and subcellular level by exposing 2-weeks-old seedlings for 7 days to total doses of 3.9 Gy, 6.7 Gy, 14.8 Gy and 58.8 Gy and evaluating growth, photosynthesis, chlorophyll a, chlorophyll b and carotenoid concentrations and antioxidative enzyme capacities. While the capacity of photosystem II (PSII measured as Fv/Fm) remained intact, plants started optimizing their photosynthetic process at the lower radiation doses by increasing the PSII efficiency (φPSII) and the maximal electron transport rate (ETRmax) and by decreasing the non-photochemical quenching (NPQ). At the highest radiation dose, photosynthetic parameters resembled those of control conditions. On subcellular level, roots showed increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) capacities under gamma irradiation but catalase (CAT), syringaldazine peroxidase (SPX) and guaiacol peroxidase (GPX) activities, on the other hand, decreased. In the leaves no alterations were observed in SOD, CAT and SPX capacities, but GPX was highly affected. Based on these results it seems that roots are more sensitive for oxidative stress under gamma radiation exposure than leaves.

ABSTRACT As photosynthesis is already known to be affected under various metal stresses, the aim of this study is to investigate uranium effects on photosynthetic parameters. Therefore, 18-day-old Arabidopsis thaliana seedlings were exposed to 50 μM uranium during 1–96 h. Uranium uptake, effects on growth parameters of roots and leaves and further responses on photosynthesis, pigment concentrations and lipid peroxidation in leaves were investigated. Uranium was highly taken up by the roots (50,352 ± 3383 μg g−1 DW at 96 h) causing complete growth arrest of the plants. Although uranium concentrations in the leaves remained low (15.0 ± 4.0 μg g−1 DW at 96 h), a remarkable photosynthetic response mechanism was observed. By chlorophyll fluorescence measurements it was observed that the potential photosynthetic efficiency (Fv/Fm) remained maximal while the effective efficiency of photosystem II (φPSII), which is a measure for the proportion of light absorbed by PSII used in photochemistry, even increased due to a decrease in non-photochemical quenching (NPQ), which indicates the conversion of excess energy into heat, but no alterations in non-regulated energy dissipation (NO). When measuring rapid light curves (RLC), giving the increase of the electron transport rate as function of irradiance, no differences were observed for the maximal electron transport rate (ETRmax) but an increase in α, representing the photosynthetic rate in the light-limited region of the RLC, was observed under uranium stress. We concluded that plant leaves start increasing their photosynthetic efficiency and decreasing their non-photochemical quenching under uranium stress.

Long-lived radionuclides such as (90)Sr and (137)Cs can be naturally or accidentally deposited in the upper soil layers where they emit β/γ radiation. Previous studies have shown that arbuscular mycorrhizal fungi (AMF) can accumulate and transfer radionuclides from soil to plant, but there have been no studies on the direct impact of ionizing radiation on AMF. In this study, root organ cultures of the AMF Rhizophagus irregularis MUCL 41833 were exposed to 15.37, 30.35, and 113.03 Gy gamma radiation from a (137)Cs source. Exposed spores were subsequently inoculated to Plantago lanceolata seedlings in pots, and root colonization and P uptake evaluated. P. lanceolata seedlings inoculated with non-irradiated AMF spores or with spores irradiated with up to 30.35 Gy gamma radiation had similar levels of root colonization. Spores irradiated with 113.03 Gy gamma radiation failed to colonize P. lanceolata roots. P content of plants inoculated with non-irradiated spores or of plants inoculated with spores irradiated with up to 30.35 Gy gamma radiation was higher than in non-mycorrhizal plants or plants inoculated with spores irradiated with 113.03 Gy gamma radiation. These results demonstrate that spores of R. irregularis MUCL 41833 are tolerant to chronic ionizing radiation at high doses.