Evidence of sulfur-bound reduced copper in bamboo exposed to high silicon and copper concentrations

We examined copper (Cu) absorption, distribution and toxicity and the role of a silicon (Si) supplementation in the bamboo Phyllostachys fastuosa. Bamboos were maintained in hydroponics for 4 months and submitted to two different Cu (1.5 and 100 μm Cu2+) and Si (0 and 1.1 mM) concentrations. Cu and Si partitioning and Cu speciation were investigated by chemical analysis, microscopic and spectroscopic techniques. Copper was present as Cu(I) and Cu(II) depending on plant parts. Bamboo mainly coped with high Cu exposure by: (i) high Cu sequestration in the root (ii) Cu(II) binding to amino and carboxyl ligands in roots, and (iii) Cu(I) complexation with both organic and inorganic sulfur ligands in stems and leaves. Silicon supplementation decreased the visible damage induced by high Cu exposure and modified Cu speciation in the leaves where a higher proportion of Cu was present as inorganic Cu(I)S compounds, which may be less toxic. - Highlights: • We examine the role of Si supplementation in mitigating Cu toxicity in bamboos. • In all plant parts, Cu was present under two oxidation states Cu(I) and Cu(II). • In stems and leaves, Cu(I) was bound to both organic and inorganic sulfur ligands. • Si supplementation decreased visible damages and modified Cu speciation. • The formation of an inorganic Cu(I)S compound may be involved in Cu storage. - Si supplementation modifies Cu speciation in a bamboo species used in phytoremediation