Potamogeton crispus was exposed to a range of external yttrium (Y) concentrations (0–30 μM) for 20 days to investigate the effects of Y accumulation on the homeostasis of elements and the photochemistry of photosystem II (PS II). Yttrium accumulation increased in a concentration-dependent manner, with most Y being associated with polysaccharides. At all Y concentrations, significant declines in relative growth rates (fresh weight basis), photosynthetic pigments, and protein content were observed, as well as an increase in leaf area damage. Yttrium accumulation disrupted elemental homeostasis, with decrease observed for concentrations of micro- and macro-elements such as Cu, Zn, Mg, Mn, and K, and increases for S, Fe, and Ca. A significant reduction in PS II photochemistry occurred in Y-treated plants, as evidenced by decrease in Fv/Fm, Fv/Fo, Fv, ψo, φEo, φRo, φPo, and PIABS, and increases in Fo, Fo/Fv, and energy fluxes per reaction center (ABS/RC, ETo/RC, TRo/RC, and DIo/RC). In addition, Y treatment significantly reduced chloroplast ATPase activity and ATP level and induced changes in chloroplast ultrastructure including an increase in plastoglobule size and organelle shape. AsA and GSH content slightly increased at 10 µM Y and then declined and that of non-protein thiol was found to be enhanced at all the Y concentrations. The results suggest that Y exposure led to general disarray of cellular functions, similar to responses observed for other trace metals.
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