根质外体屏障在水稻镉、铅吸收和积累中的作用及机制

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.

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。

镉（Cd）和铅（Pb）和在根部的径向转运过程是影响水稻地上部乃至籽粒中Pb/Cd积累的重要过程之一。然而，迄今关于质外体途径以及根质外体屏障在此过程中的作用及其与水稻地上部Cd/Pb积累特性之间的关系却鲜有研究。本研究通过室内水培、土培实验，研究了根质外体屏障在水稻Cd/Pb转运和积累中的作用与机制。结果发现，具有较强的根质外体屏障的水稻品种，其屏障对质外体流以及其中的Cd透过性较低，因此可以较有效地将Cd拦截在根部，降低通过质外体途径运输到木质部的Cd，从而减少了地上部的Cd积累。不同水稻品种之间根质外体屏障的本构性状态，以及对Cd胁迫的响应能力，共同决定了质外体屏障对质外体途径运输的Cd的拦截能力。Cd低积累品种的质外体屏障对Cd胁迫较强的响应发育能力，很可能也是导致其地上部Cd低积累的原因。不同水稻品种中与木质素、芳香栓质素单体合成相关的基因，在Cd胁迫下的差异表达模式也有所不同。上述结果表明，质外体途径参与了水稻根部对Cd的径向转运，而水稻根质外体屏障在调控Cd的转运和降低地上部Cd积累方面起着重要的作用。根质外体屏障的特征可以作为筛选Cd低积累水稻品种的重要依据。而质外体屏障与水稻地上部Pb积累之间未发现明显关系。