Influence of Silicon and Selenium and Contribution of the Node to Cadmium Allocation and Toxicity in Rice

Minimization of cadmium (Cd) in edible parts of crops is regarded as an effective approach for reducing the threat of Cd to public health. Beneficial elements selenium (Se) and silicon (Si) have been shown to promote rice growth and to reduce the rice Cd concentration under Cd stress. We performed a field experiment that highlighted the role of stem nodes and foliar Si and Se sprayings on the accumulation of Cd in 14 rice tissues, including brown rice, husk, panicle, four nodes, four internodes, and three leaves. The results indicated that foliar Se and Si applications significantly decreased brown rice Cd concentrations by 56% and 50% from 1.5 mg kg(-1) to 0.66 and 0.75 mg kg(-1), respectively. The applications of Se and Si were mainly through the reduction of the accumulation of Cd in rice roots by 27% and 32%, resulting in decreases in Cd in nodes by 53-76% and 26-60% respectively, while Cd concentrations were not significantly reduced in leaves and internodes. The first node beneath the panicle (N I) also played a critical role in the allocation of Cd within rice plants, whereas foliar Se and Si sprayings significantly reduced the extent of transfer of Cd from node I to the first internode and rice grain and significantly increased the extent of transfer of Cd to the flag leaf. However, N III had no effects on the transport of Cd to upper organs and N II promoted the translocation of Cd to upper organs after applications of Se and Si. Applications of Se and Si also improve the uptake of most of the mineral nutrients in N I. Overall, reduction of Cd in rice root and nodes and allocation of Cd in N I are the key steps in the accumulation of Cd in brown rice.