Studies On Plant Regeneration Of Mining Ecotype Sedum Alfredii And Cadmium Hyperaccumulation Of Its Callus

Heavy metal contamination in soil became more and more serious due to industrial activities and agricultural practices.Phytoremediation is a new technology for removing toxic metals from polluted soil by hyperaccumulators.Hyperaccumulators share several strategies of metal detoxification such as the synthesis of phytochelatins, glutathione,metallothioneins and organic acid,and vocuolar compartmentalization.This paper introduced the phytoremediation technology and the mechanisms of heavy metal hyperaccumulation and detoxification within the plant.Then,the effects of cadmium on callus and regenerated plants of mining ecotype Sedum alfredii Hance were investigated.An efficient micropropagation system for mining ecotype Sedum alfredii Hance,a newly identified Zn/Cd hyperaccumulator,was developed in the present study.The callus induction rate reached up to 70%from cultured leaves on MS medium with 1.00 mg l^-1 2,4-D and 0.50 mg l^-1 6-BA,and 83%from cultured stem materials grown on MS medium with 0.10 mg l^-1 2,4-D and 0.10 mg l^-1 6-BA.The callus was rapidly proliferated on MS medium containing 0.20 mg l^-1 2,4-D and 0.05 mg l^-1 TDZ.The most number of adventitious buds(17 per callus) and maximal induction rate(93%) were obtained when the calli were grown on MS medium with 2.0 mg 1^-1 6-BA and 0.3 mg l^-1 NAA.The elongation of adventitious shoots was efficiently improved at 3.0 mg l^-1 GA₃. In addition,IBA was more suitable for the rooting induction than IAA and NAA,and 21.4 roots per shoot were developed within 30 days at 2.0 mg l^-1 IBA.When these in vitro plants were grown hydroponically at 200μmol l^-1 Cd,they exhibited high efficiency of Cd transport from root to shoot and extraordinary capacity of Cd hyperaccumulation. These indicated that the regenerated S.alfredii could be used for the phytoremediation of heavy metal polluted soil.The callus of S.alfredii exhibited the characteristics of tolerating and hyperaccumulating capability to Cd.However,the Cd level in callus was only 20%of that in whole plant at 800μmol l^-1 Cd treatment.No toxicity symptpm was observed for the callus treated with 800μmol l^-1 Cd for 21 days.This was perhaps due to less Cd content in the callus compared with the whole plant.Cadmium could significantly induce PCs synthesis in the callus and PCs was detected in the callus treated with 800μmol l^-1 Cd for 6 days.Its content was increased with the elongation of Cd exposure time and reached a maximum of 80μg g^-1 at the 21th day.This indicated that PCs might play a role in Cd tolerance in the callus of S.alfredii.