Studies On The Mechanisms Of Cadmium Tolerance In Hyperaccumulating Sedium Alfredii

Heavy metal pollution is a serious environmental problem in the world on the contemporary era. To reveal the mechanism of the heavy metal tolerance and accumulation in hyperaccumulating plants will be useful to develop phytoremediation to clean heavy metal polluted sites. Grafted plants between hyperaccumulating and non-hyperaccumulating ecotypes of Sedium alfredii were generated, and suspension cells of these two kinds of S. alfredii were also induced to elucidate the mechanisms of the cadmium hyperaccumulation in S. alfredii.1. Set up the grafting system. Choosing the seedlings in vigorous growing stage and cut the stems into complementary wedge with sharp knife. Then linked the two parts of stems and roots which come from two separate seedlings and wrap up the joint with a piece of wet preservative film using a cotton thread to fasten it. The grafted seedlings were cultivated in liquid medium which had been renewed every two days. After recovering for2-3weeks, the roots of the grafted seedlings must be cut down and let them rebuild. If the roots could still grow out after going through these rebuilding process for three times, the grafted seedlings would be the proper ones to go on the following experiences.2. The chlorosis of leaves and black roots could be observed in the grafted seedlings under Cd treatments when the rootstock was from non-hyperaccumulating S. alfredii, no matter which type of S. alfredii served the shoots scion. When hyperaccumulating S. alfredii acted as the rootstock, the grafted seedling seemed much better than the former especially the shoots scion was from hyperaccumulating S. alfredii. Most Cd was detected in roots and little was found in stems and leaves of the grafted seedling with rootstock from non-hyperaccumulating S. alfredii. In the grafted seedlings with rootstock from hyperaccumulating S. alfredii and shoots scion from non-hyperaccumulating S. alfredii, the Cd content is higher in stems than in roots, but the cadmium content is lower in leaves than in stems. In the ungrafted and self-grafted hyperaccumulating S. alfredii, Cd content was most in leaves, then stems and roots. Thus it can be seen that roots play a major role in tolerance and accumulation of Cd for hyperaccumulating S. alfredii.3. The suspension cells were induced from callus of two kinds of S. alfredii and the tolerance were much stronger in hyperaccumulating ones than in non-hyperaccumulating ones under Cd pressure. BSO, the inhibitor of GSH, could reduce the ability to endure the Cd of the hyperaccumulating suspension cells without affecting the accumulating capacity. However, BSO enhanced the accumulating amount of Cd and precipitated more severe symptoms in non-hyperaccumulating suspension cells. From these results, the synthesis of GSH plays an important role in the tolerance of Cd in both hyperaccumulating and non-hyperaccumulating S. alfredii suspension cells.