Inhibition of rare earth catalytic activity by proteins

Toxic effects of heavy metal terbium ion on the composition and functions of cell membrane in horseradish roots

The environmental safety of rare earth elements (REEs), especially the toxic effect of REEs on plants, has attracted increasing attention. However, the cellular mechanism of this toxic effect remains largely unknown. Here, the toxic effects of heavy REE terbium ion [Tb(III)] on the cell membrane of horseradish roots were investigated by using electron microscope autoradiography (EMARG) and histochemical methods. The results indicated that Tb(III) was distributed in the extracellular and intracellular spaces of the roots after horseradish was treated with Tb(III). Moreover, the percentage contents of the unsaturated fatty acids in the membrane lipids, the current of the outward K(+) channel and the average diameter of membrane proteins in the roots of horseradish treated with Tb(III) were decreased; on the contrary, the percentage contents of the saturated fatty acids and malondialdehyde in the roots of horseradish treated with Tb(III) were increased. Furthermore, the contents of intracellular N, P, Mg and Fe in the roots of horseradish treated with Tb(III) were decreased, while the contents of intracellular K and Ca in the roots of horseradish treated with Tb(III) were increased. Finally, the effects of Tb(III) on horseradish roots were increased with increasing concentration or duration of Tb(III) treatment. In conclusion, after horseradish was treated with Tb(III), Tb(III) could enter the cells of horseradish roots and lead to the toxic effects on horseradish, which caused the oxidation of the unsaturated fatty acids in the membrane lipids, the changes in the membrane proteins (including the outward K(+) channel), the decrease in the membrane fluidity, and then the inhibition of the intracellular/extracellular-ion exchange in horseradish roots.

Toxic effect of heavy metal terbium ion on cell membrane in horseradish

In order to understand the toxic mechanism of terbium ion (Tb(III)) on plants, the subcellular distribution of Tb(III) in horseradish, the effect of Tb(III) on the composition of the fatty acids in the cell membrane, the peroxidation of membrane lipid, the morphological character of protoplast, the cellular ultrastructure in horseradish were investigated using transmission electron microscopic autoradiography, molecular dynamics simulation, gas chromatography, scanning electron microscopy and transmission electron microscopy. The results show that Tb(III) could not enter the horseradish cell in the presence of 5 mgL(-1) Tb(III) and it was distributed on the cell wall and plasma membrane. The behavior caused the decrease in the contents of unsaturated fatty acids and then the increase in the peroxidation of membrane lipid. Thereby the structure of horseradish cell was damaged. The effects of Tb(III) mentioned above were aggravated in horseradish treated with 60 mgL(-1) Tb(III) because Tb(III) could enter the horseradish cell. It was a possible cytotoxic mechanism of Tb(III) on horseradish.