Copper-dependent control of uptake, translocation and accumulation of cadmium in hyperaccumlator Sedum alfredii

Cadmium (Cd) is detrimental to plant growth and threatens human health. Here, we investigated the potential for remediation of Cd-contaminated soil with high copper (Cu) background using Cd hyperaccumulator ecotype (HE) Sedum alfredii. We assessed effects of Cu on Cd accumulation, compartmentation and translocation in HE S. alfredii, and compared with those in a related non-accumulator ecotype (NHE). We found that Cu supply significantly induced Cd accumulation in roots and shoots of long-term soil-cultivated HE S. alfredii. A large fraction of root Cd was accumulated in the organelles, but a small fraction was stored in the cell wall. Importantly, Cu addition reduced Cd accumulation in the cell wall and the organelles in root cells. Furthermore, leaf cell capacity to sequestrate Cd in the organelles was greatly improved upon Cu exposure. We also found that genes involving metal transport and cell wall remodeling were distinctly regulated to mediate Cd accumulation in HE S. alfredii. These findings indicate that Cu-dependent decrease of root cell-wall-bound Cd, and stimulation of efflux/influx of organelle Cd transport in root and leaf cells plays a role in the dramatic Cd hyperaccumulation expressed in naturally survived HE S. alfredii.