The copper tolerance mechanisms of Elsholtzia haichowensis, a plant from copper-enriched soils

Hydroponic cultures were conducted to investigate the effect of excessive Cu on the seed germination and growth of Elsholtzia haichowensis Sun, a Cu tolerant plant from the Tongling Cu mining sites in eastern China. Experiments were also carried out to study Cu accumulation and tolerance mechanisms of E. haichowensis seedlings. A significant decrease of seed germination was only found in the treatments with more than 750μmoll-1Cu and E. haichowensis seedlings were able to tolerate 250μmoll-1Cu in solution without growth reduction in comparison with the control group during the seed germination period. Ten micromol per litre Cu did not affect the root elongation. Higher concentrations of Cu caused the decreases of root and hypocotyl elongation, germination, and chlorophyll and carotenoids concentrations of E. haichowensis. The effect of Cu on plant growth was more pronounced in the roots than in the shoots. Up to 160μgg-1of Cu (DM) was found in the shoots of E. haichowensis treated with 500μmoll-1Cu. In all treatments, Cu concentrations were higher in the roots than that in the shoots. The results also showed that most Cu was bound on cell walls in the roots, accounting for more than 60% of the total concentration. Exposing E. haichowensis in high Cu solution elicits a large level of proteins. Through a gel filtration chromatography on Sephadex G-50, three Cu peaks were eluted out with three protein peaks.