Curium(III) and europium(III) as luminescence probes for plant cell (Brassica napus) interactions with potentially toxic metals

Highlights: • Cm(III) and Eu(III) were used as molecular probes to explore whose interactions with plant cells. • Cellular level: strong enrichment of Cm(III)/Eu(III) on Brassica napus suspension cells. • Molecular level 1: Cm(III)/Eu(III) species with a continuous distribution of slightly different M(III) surroundings. • Molecular level 2: functionalities involved are two kinds of carboxyl and phosphate groups. We have investigated the interaction of the actinide Cm(III) and its lanthanide homologue Eu(III) with cells of Brassica napus in suspension. This study combines biochemical techniques (plant cell response) with spectroscopic experiments to determine the chemical speciation of hazardous metals in contact with the plant cells. Experiments conducted over a period of 7 d showed that B. napus cells were able to bioassociate both potentially toxic metals in significant amounts up to 0.58 µmol Eu/g_{fresh cells} and 1.82 µmol Cm/g_{fresh cells} at 30 µM Eu(III) and 0.68 µM Cm(III), respectively. For Cm(III), a biosorption process could be identified as soon as 5 h post-exposure with 73 ± 4% of the Cm(III) bioassociated. Luminescence spectroscopy results based on UV and site-selective excitation confirmed the existence of three Cm(III)/Eu(III) [M(III)] species in both the supernatants and cells. The findings detailed herein support that M(III) coordinates to two kinds of carboxyl groups and phosphate groups.