Subcellular And Molecular Distributions Of Cadmium In Two Rice Cultivars With Different Tolerance

As the development of industrial and agricultural, the number of Cd come into the environment is increasing daily. The paddyfield soil polluted by Cd has become more and more serious, which lead to the excess of Cd content in rice and seriously affecting human health. There is obviously different between species for Cd obsorption, accumulation and tolerance in rice. Therefore, to select rice varieties with high tolerance and less translocation, it’s significant to definitize the mechanism of Cd accumulation in different parts of rice. In this paper, two different Cd tolerance of rice N07-6(sensitive), and N07-63(tolerance) were planted in hydroponic experiment. And from the subcellular level, Cd accumulation and distribution was measured and analysed. The main results are as follows:1. Relationship between the Cd tolerance of rice and nonprotein thiols (NPT) contentNPT is a class of thiol-rich material, can complexed with free Cd-ion effectively. The NPT content in different parts of rice treated with50μmol·L-1Cd was comparetive analysis. The results showed that Cd induced increases of NPT content for the two cultivars, and the increment of N07-63was siginificantly higher than N07-6. The content of Cd and NPT in root of N07-63were higher siginificantly than that of N07-6, whereas less siginificantly than N07-6for translocation ratio. These illuminate that Cd combins with NPT and transferred to the vacuole, which can reduce the translocation of Cd from root to shoot, as well as alleviate poison for shoot of rice.2. Relationship between the Cd tolerance of rice and subcellular and molecular distribution of CdThe results compared with the subcellular distribution of Cd found that most Cd was distributed in cell wall and cellular soluble fraction. N07-63had higher proportions of total Cd in the cell wall of shoot and root, but lower in the cellular soluble. Thses show the mechanism of Cd tolerance in root is that:most of Cd is accumulated in the cell wall, to reduce the translocation of Cd from root to shoot and alleviate poison for cell.From the molecular distribution of Cd in rice, we observed that Cd was associated partly with protein with large molecular weight in shoot cellular soluble fraction. The rest was mainly bound to phytochelations (PCs). However, most Cd was complexed with PCs in rice root, and the association between Cd and PCs was stronger in N07-63than that in N07-6. It explains that the N07-63synthetic capacity of PCs is stronger; the content of Cd-PCs is higher. Thus N07-63has a better Cd tolerance.3. Effect of H2O2pretreatment on Cd subcellular and molecular distribution of riceAfter pretreatment of100μmol·L-1H2O2and treatment of50μmol·L-1Cd, Cd content in cell wall of N07-6shoot reduced siginificantly, whereas increased siginificantly in cellular soluble fraction of N07-63shoot. Cd content of two rice cultivars of subcellular components in root had no siginificant difference. After H2O2pretreatment, NPT content in root increased siginificanf. While Cd content in cellular soluble of root had a slight increase, Cd content in cell wall of root had a falling trend. This indicates that H2O2pretreatment may have affected the cell wall binding of Cd. There are more NPT complexed with Cd-ion in cellular soluble fraction.The molecular distribution in rice root can be seen that:H2O2pretreatment didn’t affect the distribution of Cd associated with different molecular weight protein. The content of thiol from large molecular weight protein combinated Cd increased slightly. But the content of thiol from PCs reduced slightly. It might be that H2O2pretreatment inhibited the decomposition of protein with large molecular weight.In summary, the effect of H2O2pretreatment on Cd subcellular and molecular distribution of rice, is due to H2O2affects indirectly the biochemistry processes in rice as a signal transduction.