Plant regeneration of the mining ecotype Sedum alfredii and cadmium hyperaccumulation in regenerated plants

An efficient micropropagation system for mining ecotype Sedum alfredii Hance, a newly identified Zn/Cd hyperaccumulator, was developed. Frequency of callus induction reached up to 70% from leaves incubated on Murashige and Skoog (MS) medium supplemented with 1.0 mg l(-1) 2,4-dichlorophenoxy acetic acid (2,4-D) and 0.5 mg l(-1) 6-benzyladenine (BA), and 83% from internodal stem segments grown on MS medium with 0.1 mg l(-1) 2,4-D and 0.1 mg l(-1) BA. Callus proliferated rapidly on MS medium containing 0.2 mg l(-1) 2,4-D and 0.05 mg l(-1) thidiazuron. The highest number of adventitious buds per callus (17.3) and frequency of shoot regeneration (93%) were obtained when calli were grown on MS medium supplemented with 2.0 mg l(-1) BA and 0.3 mg l(-1) alpha-naphthalene acetic acid (NAA). Elongation of shoots was achieved when these were incubated on MS medium containing 3.0 mg l(-1) gibberellic acid. Induction of roots was highest (21.4 roots per shoot) when shoots were transferred to MS medium containing 2.0 mg l(-1) indole 3-butyric acid rather than either indole 3-acetic acid or NAA. When these in vitro plants were acclimatized and transferred to the greenhouse, and grown in hydroponic solutions containing 200 mu M cadmium (Cd), they exhibited high efficiency of Cd transport, from roots to shoots, and hyperaccumulation of Cd.