Investigations on the Eu(III) translocation in hydroponically grown plants

Lanthanides (Ln) have become indispensable for science, technology and everyday objects. The intense
exploitation of Ln-bearing ores, their further processing as well as the improper disposal of high-tech
products lead to anthropogenic increased levels of these metals in the environment. Knowledge about their
fate in the plant biosphere is crucial to maintain food safety and to develop feasible phytoremediation
strategies.
In our research, we aim to follow Eu(III) on its journey through hydroponically grown sand oat (Avena
strigosa) – a potential candidate for phytoremediation – from initial exposure and cellular uptake over
localization in root tissue followed by translocation via plant sap into aboveground parts and the metal’s
distribution in leaves. Therefore, we apply a set of spectroscopic (TRLFS, ICP-MS), microscopic (chemical
microscopy), chromatographic (HPLC) and photographic (autoradiography) analysis techniques. In short,
following an exposure time of 96 h with 200 μM Eu(III), chemical microscopy reveals roots hairs and root
tips a s well as epidermis cells to be one uptake pathway for the Ln. Quantification of the metal content in
roots and shoots by ashing and subsequent acid digestion unveils that the majority of Eu(III) accumulates
in the roots (≈14242 μg/gdry weight) whereas only 35 μg/gdry weight) is translocated into the green plant parts.
The upwards transport of Eu(III) takes place via the xylem sap, in which organic acids are probably
responsible for Eu(III) translocation in measurable quantity. In order to visualize not solely the microscopic
distribution of Eu(III) in roots, but also account for the shoots, experiments with the radioactive isotope
Eu-152 were conducted and the dried plant was scrutinized by autoradiography (Fig. 1).
These studies contributed to a comprehensive understanding of the fate of Ln(III) in plants. Investigations
regarding the uptake and distribution of Cm(III) are currently under way.