Study On Trait Of Brassica Juncea Hyperaccumulating Cd And Pb From The Soil Contaminated With These Heavy Metals

Brassica juncea is a new heavy metal hyperaccumulater, which holds a large potential in remedying heavy metal-polluted soils. Studies on Brassica juncea mainly paied attention to its capacity of uptake and accumulation and efficiency of remedying heavy metals in soils.However, it is necessary deeply to study the trait and mechanism of Brassica juncea hyperaccumulating heavy metals from the soil contaminated with these heavy metals. Therefore, the pot and rhizo-bag experiments were carried out with orthogonal regression design of two factors (Cd and Pb) in five levels, while Brassica juncea and rape were used as studied plant and comparing plant, respectively. Through the comparison analysis of the responses of Brassica juncea and rape under the combined stresses of Cd and Pb to reveal the characteristics and capacities of uptaking and accumulating heavy metals, the physiological and biochemical characteristics and rhizosphere character of Brassica juncea. Main results of the experiments were summarized as follows:1. While the contents of Cd and Pb were lower, the compound contamination of Cd and Pb is slight effects on the growth of Brassica juncea. But with increasing of Cd and Pb contents, when the contents of Cd and Pb respectively are over 100mg·kg^-1 and 500mg·kg^-1, the biomasses of shoot and root are remarkably decreased. Cd contributed to biomass more than Pb. Compared with rape, Brassica juncea has higher biomass and stronger tolerance to heavy metals.2. Under compound contamination of Cd and Pb, Cd and Pb contents in shoot and root of Brassica juncea not only affected by the added Cd and Pb contents respectively, but also by co-existent heavy metal element in soil. The interaction of Cd and Pb indicates that Cd not only inhabited Pb uptake of roots, but also inhabited Pb transference from roots to shoots, while Pb not only enhanced Cd uptake of roots, but also enhanced Cd transference from roots to shoots. The results also indicate that the capacity of Brassica juncea hyperaccumulating Cd is stronger than Pb. Cd and Pb contents in roots of Brassica juncea are higher than those in the shoots.3. Under compound contamination of Cd and Pb, the contents of chlorophyll in leaves of Brassica juncea is less than that of the CK obviously, while higher than that of the rape treatment; the contents of MDA in leaves of Brassica juncea is higher than that of the CK, while less than that of the rape treatment. Cd contributed more to chlorophyll and MDA than Pb. The compound contamination of Cd and Pb gave different effects on three protective enzymes. With increasing of Cd and Pb contents, the SOD activity in leaves of Brassica juncea increases remarkably, while the POD and CAT activities are activated by lower contents of heavy metals and inhabited by higher contents. The CAT activity indicates more sensitive than POD activity. Hence SOD activity gave main protective for Brassica juncea.4. In the rhizo-bag experiment, pH in rhizosphere of Brassica juncea is significantly lower than that of the non-rhizosphere. The contents of available Cd and Pb in rhizosphere of Brassica juncea are significantly higher than that of the non-rhizosphere, also higher than that of rape treatments. pH plays an important role in mobilization of Cd and Pb in soil and Cd and Pb uptake by Brassica juncea under Cd and Pb compound contamination.