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| Home > Publications database > Understanding the toxicity of arsenic, cadmium and copper in the model plant Ceratophyllum demersum using μXRF tomography and μ-XANES |
| Home > Publications database > Understanding the toxicity of arsenic, cadmium and copper in the model plant Ceratophyllum demersum using μXRF tomography and μ-XANES |
| Conference Presentation (Other) | DESY-2014-01347 |
2013
Abstract: Heavy metal uptake in plants is an important area not only for basic research, but also because of its impact on human nutrition and its application for the phytoremediation of contaminated soils. One of the most interesting topics in this area of research is the localisation and speciation of toxic metals&metalloids (e.g. As, Cd, Cu, Zn) inside the plant (e.g. [1], [2]). Here, we analyzed the distribution of non-hyperaccumulated As, Cd, Cu and Zn in the metal-sensitive shoot model plant Ceratophyllum demersum by µ XRF, and furthermore studied tissue-specific As speciation in the same sample using confocal µ XANES [3-5]. Samples of living leaves were prepared in capillaries, shock-frozen in supercooled isopentane, and maintained frozen-hydrated at about 100 K throughout the measurement. Elements in micro X-ray fluorescence (µ XRF) tomograms were quantified using standard-filled capillaries including a tomographic correction for X ray absorption in the sample. Measurements of As-stressed plants revealed that As was mainly sequestered in the epidermis. However, increasing As in the nutrient solution from 1 µM to 5 µM resulted in further increase of As in the vein and mesophyll but not in the epidermis of young leaves. Copper was mainly localized in the vein, and it did not change upon As exposure. In contrast, Zn was homogenously distributed over the whole leaf in control plants, but with increasing As, Zn was exported more towards the epidermis [3]. The in situ speciation of As in the same leaves was performed through µ XANES coupled to confocal detector optics. Thus we could distinguish As speciation at the tissue level i.e. epidermis, mesophyll and vein tissues (including xylem, phloem and separating tissue in between). The epidermis of a mature leaf contained the highest proportion of thiol-bound As (mostly with PCs), while in young leaves a lower proportion of As was thiol-bound. Further, at higher As concentrations the percentage of unbound AsIII increased in the vein and mesophyll of young leaves. Micro-XRF of Cd exposed plant leaves revealed changing distribution patterns of Cd and Zn at non-toxic (0.2 nM, 2 nM), moderately toxic (20 nM) and lethally toxic (200 nM) levels of Cd. Increasing Cd 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 along with Cd, indicating an inhibition of their export from the vein [4]. At deficient and optimal copper supply, Cu was mainly localized in the vein. Copper deficiency did not alter the Cu distribution pattern, but lowered the tissue concentrations. In contrast, at toxic Cu after two weeks Cu was sequestered from veins towards the mesophyll and epidermis, with Cu concentrations in the epidermis reaching about half of the concentration in the vein. Longer treatment did not further increase the epidermal copper accumulation, but only Cu accumulation in the vein. Zn content of the leaves was reduced by increasing copper. Cu deficiency did not only increase Zn accumulation in the leaves, but also changed Zn distribution. While at optimal and toxic Cu, Zn was rather homogeneously distributed throughout the leaves, at deficient copper supply the additionally accumulated Zn was sequestered to the epidermis [5].References[1] H. Küpper, P.M.H. Kroneck, In: Metal Ions in Biological Systems, Volume 44, Chapter 5. (Eds: Sigel A, Sigel H, Sigel RKO). Marcel Dekker, Inc., New York; pp. 97-142 (2005)[2] E. Andresen, H. Küpper, Chapter 13, Volume 11 of series "Metal Ions in Life Sciences". (Eds: Sigel A, Sigel H, Sigel RKO). Springer Science + Business Media B.V., Dordrecht; pp. 395-414 (2013)[3] S. Mishra, G. Wellenreuther, J. Mattusch, H.-J. Stärk, H. Küpper, (in preparation for submission; 2013) [4] E. Andresen, J. Mattusch, G. Wellenreuther, G. Thomas, U.A. Abad, H. Küpper, (submitted to Metallomics, 2013)[5] G. Thomas, H.-J. Stärk,, G. Wellenreuther, Bryan C. Dickinson, H. Küpper, Aquatic toxicology, Early View: http://dx.doi.org/10.1016/j.aquatox.2013.05.008 (2013)
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