Influence of uranium(VI) on the metabolism of plant cells

Detailed knowledge of the radionuclide transfer in the environment including the food chain represents the basis for the reliable assessment of the resulting risk potential for human and wildlife. In order to improve the knowledge of the underlying processes, interaction processes of plants with actinides are studied (e.g., [1-3]). Due to the interaction with heavy metal ions, plants segregate metal chelates into the rhizosphere, store metal chelates in vacuoles or synthesize protective metabolites that can bind metal ions and consequently reduce their availability in the cytoplasm [4].

In the present work we study the interaction of uranium(VI) with canola cell suspensions (Brassica napus) as a function of the uranium(VI) concentration. The influence of uranium(VI) on the cell metabolism is studied by microcalo-rimetry. Our results show that in the presence of uranium(VI) concentrations >100 µM the heat flow generated by the cells is decreased, which indicates a lower metabolic activity of the cells compared to control samples cultivated in the absence of uranium(VI). These results agree to cell viability data measured applying the MTT test [5]. Furthermore, we study the release of plant cell metabolites in consequence of the cell contact with uranium(VI). Focusing on flavonoids, flavonoid glycosides, and phenolic acids, a solid phase extraction method coupled with high-performance liquid chromatography is developed. This method allows the separation and enrichment of cell metabolites from the nutrient medium as well as their fractionation as basis for their further identification. Knowledge of an element’s speciation is crucial for understanding its biochemical and biological behavior. Therefore, the uranium(VI) speciation in the nutrient medium is determined by time-resolved laser-induced fluorescence spectroscopy and calculated by thermodynamic modeling. The objective is to correlate the influence of uranium(VI) on the metabolic activity of the cells with the uranium(VI) speciation in the nutrient medium.

ACKNOWLEDGEMENTS
The authors thank J. Seibt, S. Heller, J. Philipp, and S. Gurlit for their technical support.

REFERENCES
[1] Günther, A. et al. (2003) Radiochim. Acta 91, 319-328.
[2] Laurette, J. et al. (2012) Environ. Exp. Bot. 77, 96-107.
[3] Geipel, G. et al. (2015) Biometals 28, 529-539.
[4] Weiler, E., Nover, L. (2008) Allgemeine und molekulare Botanik, Thieme, Stuttgart.
[5] Mosmann, T. (1983) J. Immunol. Meth. 65, 55-63.