水稻铵-镉互作的生理与分子调控机制

Cadmium (Cd) contamination in paddy soil is a serious problem in China, and Cd accumulation control has become an important issue in rice safety production. Nitrogen as a macro-element could strongly affect Cd accumulation in rice. It is documented that Cd accumulation was closely related to the application of nitrogen form and dosage, with nitrate enhanced while ammomium inhibited Cd accumulation in rice. However, the regulation mechanisms of rice Cd accumulation under ammomium supply are still ambiguity. Cd is mainly absorbed through divalent metal ions (such as Fe2+, Mn2+) transport proteins in root, and re-transport among plant organs with PCs-Cd basic forms. However, these transporter genes expression are regulated by nitric oxide, a key signaling molecular. We speculate that ammonium could feedback and inhibit the activities of nitrate reductase and nitrite reductase, which product nitric oxide in plant, and further impact on Cd uptake and accumulation. This project will use two rice varieties differing in cadmium accumulation as materials. Analyze and reveal the nitric oxide-mediated ammomium-Cd interactive mechanism at physiological and molecular level under different combined treatments of ammonium and Cd. The project provides a basis for rational nitrogen application to reduce Cd accumulation, and further improving the safety theory in Cd pollution area in rice.

我国农田镉污染日益严重，稻米镉污染控制已成为粮食安全生产的重要课题。氮作为作物最重要的三大营养元素之一，可强烈影响水稻镉积累。研究发现水稻镉积累与氮形态和用量关系密切，硝态氮促进镉在稻米中的积累，而铵抑制镉积累并表现拮抗作用。然而，关于铵调控水稻镉积累的机理依然模糊。镉主要通过二价金属离子(比如铁、锰离子)转运蛋白被根系吸收，并以PCs-Cd等多种形式在植株不同器官中转运，这些转运蛋白基因表达又受一氧化氮信号调节。我们推测铵反馈抑制硝酸还原酶/亚硝酸还原酶活性，抑制一氧化氮的产生从而影响水稻镉积累。本研究拟利用镉积累有差异的籼稻品种，设置不同铵镉处理，利用生理和分子手段解析和揭示一氧化氮介导铵-镉互作的生理与分子调控机制，为合理施氮降低稻米镉积累提供依据，进一步完善水稻镉污染控制安全理论。

我国农田镉污染问题日益严峻，稻米镉污染控制已成为粮食安全生产的重要课题。镉主要通过二价金属离子转运蛋白被根系吸收，并以PCs-Cd等多种形式在植株不同器官中转运，这些转运蛋白基因表达受铵调控。本项目系统阐述了氮对植物镉的调控机理，明确铵调控水稻镉积累的生理及分子机制。主要结果如下：1）采用粳稻品种日本晴，进行不同浓度铵-镉处理，铵+硝化抑制剂显著抑制水稻根系对镉的吸收，增加了地上部镉含量及积累量，且随着铵施用浓度的增加而增加。在土培条件下，随铵浓度增加水稻籽粒中镉含量也表现出明显的增加趋势，镉污染稻田提高铵用量增加了稻米镉危害。2）水培条件下，水稻根部和地上部铵含量、氮含量、一氧化氮（NO）含量、可溶性蛋白含量随铵浓度增加而增加，而铵显著影响水稻根部NPTs、GSH、PCs含量及OsMT-1表达量，铵促进了镉在水稻根部的螯合及形成PCs-Cd转运复合体。3）铵显著抑制水稻镉吸收基因OsIRT1、OsNramp5、OsLCD、OsHMA3表达，铵抑制镉的吸收和液泡固定，而随着铵浓度增加，根部OsLCT1、OsHMA2和OsNramp1表达量增加，铵通过这些分子机理促进了镉从根部向地上部的转运。4）NO信号分子参与了铵对水稻镉的解毒作用，镉胁迫显著降低水稻根长、株高、分蘖、光合及蒸腾速率，增加了MDA和H2O2含量，铵通过增加POD和APX活性缓解镉毒害，NO参与了解毒过程。与此相关，利用不同铵比例验证了铵-镉互作的结果，利用MutMap和RNA-seq方法分析低镉积累水稻OsLCD1突变体的分子机制及镉胁迫下的基因表达，也明确了水杨酸缓解农作物镉毒害的作用机制，分析了NO信号分子在水杨酸缓解镉毒害的作用。发表论文4篇，其中SCI论文3篇，以第一完成人授权国家发明专利1项，软件著作权1项。本项目为通过合理利用铵及其拮抗作用降低水稻镉积累，丰富了水稻镉污染控制理论。