Molecular distribution and toxicity assessment of yttrium in Elodea canadensis

Aquatic plants are known to accumulate and bioconcentrate metals. In the present study, Elodea canadensis was subjected to different concentrations of yttrium (Y), ranging from 0 to 200M, for 7 days and analysed for subcellular distribution and molecular localisation of Y, accumulation of mineral nutrients in leaf tissue, changes in photosynthetic pigments, oxidative stress and leaf and organelle ultrastructure. Leaf fractionation by differential centrifugation indicated that 68-76% of Y was accumulated in the cell wall, with higher levels of accumulation in cellulose and pectin than in other biomacromolecules. At all Y concentrations tested, Ca, Mg and Mn levels decreased in E. canadensis, whereas P levels increased; Fe and K levels increased initially and then declined. There was a marked concentration-dependent reduction in photosynthetic pigments following exposure to Y. Responses of components of the antioxidant system to Y treatment varied, whereas there were marked increases in reactive oxygen species and malondialdehyde at all Y concentrations tested. In addition, morphological symptoms of aging, such as chlorosis and damage to chloroplasts and mitochondria, were induced even by the lowest Y concentration. The results reveal that exogenous Y is widely available to this aquatic plant, which may have negative effects on aquatic organisms.