稻米Cd、Pb超标是当前我国水稻生产迫切需要解决的重要问题，筛选和种植对这两种元素低积累的品种被认为是在污染稻田上生产安全大米的一条有效途径。深入了解哪些内部因素决定水稻对这两种元素的吸收和积累可为品种选育提供科学依据。我们的预实验结果提示，根质外体屏障在水稻Cd、Pb吸收和积累过程中很可能起重要作用，但其作用及相关机理需要进一步明确。本项目拟利用已筛选的具有不同Cd、Pb积累特征的水稻品种为材料，通过一系列实验，研究和分析这些品种根质外体屏障的特征/通透性，根质外体途径在Cd、Pb转运中的权重及其与水稻各器官中Cd、Pb含量之间的关系，明确质外体屏障在水稻Cd、Pb吸收和积累中的作用、所涉及的机制及其关键特征指标。研究结果将从根内部结构的角度揭示不同水稻品种对Cd、Pb积累存在显著差异以及一些品种具有Cd和Pb共低积累特性的原因，为选育Cd、Pb低积累品种提供理论依据和方法。

Rice contaminated by cadmium (Cd) and lead (Pb) is increasingly concerned and this problem requires an urgent resolution. Screening and breeding rice cultivars with low concentrations of these toxic elements in their grain is considered to be a promising way forward for producing safe rice from Cd/Pb-contaminated paddy fields. The understanding of the internal mechanisms which play key roles in Cd and Pb uptake and accumulation in rice plants will benefit the screening of suitable low accumulating cultivars. Results from our pilot experiments suggest that root structures (especially the root apoplastic barrier) may play important roles in Cd and Pb uptake and accumulation in the rice plant. However, these roles and related mechanisms still require further study. The aims of this project are thus to study the relationships between these characteristics and the permeability of the apoplastic barriers, as well as the contribution of apoplastic pathway in Cd and Pb radial translocation, and the concentrations of Cd and Pb in different plant tissues of selected rice cultivars with different abilities in accumulating Cd and Pb in grains. We will thus elucidate the roles of the root apoplastic barrier in Cd and Pb uptake and accumulation in rice plants and related mechanisms. The results will be valuable in revealing the reasons why there are large differences in Cd/Pb accumulation between rice cultivars, and why some cultivars exhibit both low Cd and Pb accumulation so that the selection of cultivars for use in heavy metal-contaminated lands will surely be benefited.