Synchrotron X-rays reveal the modes of Fe binding and trace metal storage in the brown algae Laminaria digitata and Ectocarpus siliculosus

Funding Funding from the UK Natural Environment Research Council (NERC) through grants NE/D521522/1, NE/F012705/1, and Oceans 2025 (WP4.5) programs to FCK; the National Science Foundation (CHE-1664657) and the National Oceanic & Atmospheric Administration to CJC and FCK; and the MASTS pooling initiative (Marine Alliance for Science and Technology for Scotland, funded by the Scottish Funding Council and contributing institutions; grant reference HR09011) is gratefully acknowledged by FCK. PK would like to thank the European Commission for her postdoctoral fellowship (EC-Horizon 2020-MSCA-IF, grant no. 839151). AM and HK thank the Ministry of Education, Youth and Sports of the Czech Republic with co-financing from the European Union (grant "KOROLID", CZ.02.1.01/0.0/0.0/15_003/0000336) and the Czech Academy of Sciences (RVO: 60077344). AM, FK and HK are grateful for support from the European Community in the framework of the Access to Research Infrastructure Action of the Improving Human Potential Program to the ESRF (experiment LS-2772, beamline ID16AI). AM and HK thank Czech Government funding (Členství v European Synchrotron Radiation Facility, MŠMT – 33914/2017-1) supporting their work at the ESRF. GeoSoilEnviroCARS is supported by the National Science Foundation – Earth Sciences (EAR – 1634415) and Department of EnergyGeoSciences (DE-FG02-94ER14466). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Computational resources were supplied by the project "e-Infrastruktura CZ" (e-INFRA CZ LM2018140) supported by the Ministry of Education, Youth and Sports of the Czech Republic.Peer reviewedPublisher PD

Dual detector micro-XRF cryotomography and mapping on the model organism Daphnia magna

The recent availability of a cryostream cooler at beamline L has allowed synchrotron radiation based micro-XRF analysis of frozen biological samples close to their native state. In a previous contribution, we compared the elemental distributions within a ydrated (frozen) and a fixed (dehydrated) Daphnia magna, which is a freshwater crustacean used in toxicological research as a model organism for evaluating effects of metals on the cosystem. Although hydrated samples show less dislocation of elements and/or sample contamination as compared to fixed samples, they are mainly composed of a water matrix, which is more susceptible to absorption effects of low energy X-rays. Therefore, we investigate the degree of absorption in 2D/CT micro-XRF elemental maps of Daphnia magna using a dual silicon drift detector (SDD) setup

Fast EXAFS in synchronous scanning mode at PETRA P06

First fast EXAFS spectra have been successfully measured at the Hard X-ray Micro-probe Beamline P06 (PETRA III) synchronously scanning the U32 undulator gap and the monochromator Bragg axis. Stability and spatial homogeneity of the beam are proved to be the limiting factors for the quality of the EXAFS spectra, whereas the performance of the data acquisition electronics limits the energy resolution when total scan time is reduced to 30 seconds. Results of the test measurements give us the estimate of the utmost performance of 5-10 seconds per full EXAFS scan considering certain hardware modifications

Speciation and Distribution of Arsenic in the Nonhyperaccumulator Macrophyte Ceratophyllum demersum

Although arsenic (As) is a common pollutant worldwide, many questions about As metabolism in nonhyperaccumulator plants remain. Concentration- and tissue-dependent speciation and distribution of As was analyzed in the aquatic plant Ceratophyllum demersum to understand As metabolism in nonhyperaccumulator plants. Speciation was analyzed chromatographically (high-performance liquid chromatography-[inductively coupled plasma-mass spectrometry]-[electrospray ionization-mass spectrometry]) in whole-plant extracts and by tissue-resolution confocal x-ray absorption near-edge spectroscopy in intact shock-frozen hydrated leaves, which were also used for analyzing cellular element distribution through x-ray fluorescence. Chromatography revealed up to 20 As-containing species binding more than 60% of accumulated As. Of these, eight were identified as thiol-bound (phytochelatins [PCs], glutathione, and cysteine) species, including three newly identified complexes: Cys-As(III)-PC2, Cys-As-(GS)2, and GS-As(III)-desgly-PC2. Confocal x-ray absorption near-edge spectroscopy showed arsenate, arsenite, As-(GS)3, and As-PCs with varying ratios in various tissues. The epidermis of mature leaves contained the highest proportion of thiol (mostly PC)-bound As, while in younger leaves, a lower proportion of As was thiol bound. At higher As concentrations, the percentage of unbound arsenite increased in the vein and mesophyll of young mature leaves. At the same time, x-ray fluorescence showed an increase of total As in the vein and mesophyll but not in the epidermis of young mature leaves, while this was reversed for zinc distribution. Thus, As toxicity was correlated with a change in As distribution pattern and As species rather than a general increase in many tissues

Different strategies of cadmium detoxification in the submerged macrophyte Ceratophyllum demersum L.

The heavy metal cadmium (Cd) is highly toxic to plants. To understand the mechanisms of tolerance and resistance to Cd, we treated the rootless, submerged macrophyte Ceratophyllum demersum L. with sub-micromolar concentrations of Cd under environmentally relevant conditions. X-ray fluorescence measurements revealed changing distribution patterns of Cd and Zn at non-toxic (0.2 nM, 2 nM), moderately toxic (20 nM) and highly toxic (200 nM) levels of Cd. Increasing Cd concentrations led to enhanced sequestration of Cd into non-photosynthetic tissues like epidermis and vein. At toxic Cd concentrations, Zn was redistributed and mainly found in the vein. Cd treatment induced the synthesis of phytochelatins (PCs) in the plants, with a threshold of induction already at 20 nM Cd for PC3. In comparison, in plants treated with Cu, elevated PC levels were detected only at the highest concentrations (100–200 nM Cu). Our results show that also non-accumulators like C. demersum store toxic metals in tissues where the heavy metal interferes least with metabolic pathways, but remaining toxicity interferes with micronutrient distribution. Furthermore, we found that the induction of phytochelatins is not proportional to metal concentration, but has a distinct threshold, specific for each PC species. Finally we could show that 20 nM Cd, which was previously regarded as non-toxic to most plants, already induces detoxifying mechanisms