Physiological dissection of cobalt/copper tolerance and hyperaccumulation in the plants of south-central Africa

摘要

The mechanisms of metal tolerance and hyperaccumulation in plants are of great interest, especially in phytoextraction of valuable metals such as cobalt (Co) and copper (Cu) from contaminated land and mineral wastes. A hydroponic system was used to investigate the tolerance and accumulation capacity of Co and Cu in the Co/Cu hyperaccumulators Haumaniastrum robertii and Crotalaria cobalticola in comparison with the common pasture species Tri folium subterraneum. Elemental distributions in the leaves at the subcellular level were analyzed by NanoSIMS. Resuits showed that both hyperaccumulators could tolerate and hyperaccumulate Co in hydroponics;H. robertii accumulated Co to concentrations greater than 1% of shoot dry biomass. Both hyperaccumulators exhibited about a 10-fold higher shoot/root Co- concentration quotient than did T. subterraneum, suggesting that these Cohyperaccumulators possess specific mechanisms to translocate large amounts of Co from roots to shoots. H. robertii and C. cobalticola could also tolerate high concentrations of Cu in hydroponics without hyperaccumulating Cu in the shoots. NanoSIMS images suggested that Cu was present predominantly in the cell walls surrounding the epidermal cells in H. robertii. This Cu 'exclusion' from the interior of the cells may be the basis of the extraordinarily high degree of Cu tolerance shown by this species.