Mechanism Of Metallothionein EiMT2for Accumulating Cd And Zn In Eichhornia Crassipes

Since Eichhornia crassipes has merits of strong clean ability, widely ecological adaptability, growing fast, hyperaccumulating heavy metals simultaneously and so on, it has been extensively used in phytoremediation of polluted water. Although people developed many researches to focus on efficiency of bioremediation to the toxic metals, few elucidated the involved molecular mechanism. This thesis describes the mechanism of Eichhornia crassipes metallothionein2(EiMT2) for accumulating Cd and Zn in the plant. The study shows the main results as follows:1. The bioconcentrating capacity and tolerance ability of Eichhornia crassipes for Zn are larger than Cd. Its tolerance threshold is1mg·L-1Cd,30mg-L"1Zn. Cd and Zn are mostly accumulated in root, but will be transferred to leaves and stems with increasing heavy-metal levels.2. Under a range of concentrations of Cd and Zn in the ambient water, the state of02. H2O2flux in all parts of Eichhornia crassipes increase first and then decrease. O2is always influx. More interesting is that the state of H2O2flux in roots and leaves is always outfluxing but influxing in stems at the beginning and then outfluxing. Changes of state of H2O2flux may be used to predict metabolic system close to out of balance under certain level of heavy metals, providing evidence about tolerant ability of the plants to heavy metals. Meanwhile, the activities of SOD, CAT and APX in Eichhornia crassipes vary widely. However, they are changing similarly, at lower heavy-metal concentrations but inhibited at higher concentrations. In addition, K+channel may take an active part in regulation of bioaccumulation of heavy metals in the plant.3. Heavy metals can induces the expression of water soluble proteins of less than43kDa. Their expressions are stimulated at low metal concentrations but inhibited at higher concentrations.4. The effects of Cd and Zn on expression of EiMT2in different parts of Eichhornia crassipes are quite different. However, EiMT2is mostly expressed in roots under stresses of both Cd and Zn. It reaches the climax in roots at1mg·L-1Cd and40mg·L-1Zn, respectively. Apart from scavenging ROS, EiMT2also plays an important role in hyperaccumulation of heavy metals, especially Cd, in the plant. It has to be noted that some more molecules may directly contribute to Zn hyperaccumulation.