Synergistic effects between [Si-hemicellulose matrix] ligands and Zn ions in inhibiting Cd ion uptake in rice (Oryza sativa) cells.

Abstract

Our study demonstrated that Zn alleviated Cd toxicity in the presence of Si in the cell walls by Zn 2+ binding to ligands through the formation of the [Si-hemicellulose matrix]Zn complexes that restrict the uptake of Cd. The plant cell wall exhibits preferential sites for the accumulation of metals at toxic concentrations. Through modification of wall polysaccharide components, elements, such as silicon (Si) and zinc (Zn), may play active roles in alleviating the toxicity of heavy metals, including cadmium (Cd). However, enhanced tolerance for Cd stress may rely on synergistic effects between nutrient elements. Here, we cultured Si-accumulating suspension cells of rice (Oryza sativa) exposed to Cd and Zn treatments, either separately or in combination, and investigated cells using noninvasive microtest technology (NMT), inductively coupled plasma mass spectroscopy (ICP-MS) and atomic force microscopy (AFM). We found that Zn alleviated Cd toxicity in the presence of Si in the cell walls by binding of Zn2+ to ligands through the formation of the [Si-hemicellulose matrix]Zn complexes and co-precipitates to greatly inhibit Cd2+ uptake into cells. This, in turn, induced the lower expression of Cd-related transporters. This synergistic effect could be decisive for the survival of cells under conditions of high Cd concentrations.