基施螯合铁对水稻根部铁镉吸收和阻隔策略研究

Iron (Fe) deficiency and cadmium (Cd) pollution are two important research areas in the fields of plant nutrition and phytoremediation, and interestingly Cd uptake in rice (Oryza sativa L.) is documented to be mediated by Fe transport system in the root. Our recent works have showed that soil application of Fe chelates could facilitate Fe uptake but inhibit Cd bioaccumulation by rice plants as well. However, the uptake mechanisms by rice plants in the presence of Fe chelates remain speculative. The proposed project would investigate the Fe/Cd uptake processes after the basal application of three model Fe chelates (i.e., EDDHAFe(III), EDTANaFe(III) and EDTANa2Fe(II)): 1) predict the changes in bioavailability of Fe and Cd in rice rhizosphere by a combination of laboratory measurements (i.e., ion exchange technique, membrane dialysis, and soil solution extraction) and geochemical modelling (i.e., PHREEQC and Geochem-EZ); 2) analyze adsorption, uptake and distribution of Fe and Cd in root micro-zone plaque, apoplast and symplast by chemical separation, SEM-EDS, Non-invasive Micro-test Technology (NMT) and absorption kinetic methods; and 3) explore Fe and Cd speciation in root xylem and the underlying molecular mechanisms by the techniques of HPLC-MS and QRT-PCR. The project would improve our understandings of the beneficial effects of Fe chelates on Fe biofortification and mitigation of Cd accumulation by rice plants, which might pave a path for the future application of Fe chelates into widely Cd contaminated paddy soils in China.

铁缺乏和镉污染是目前植物营养和植物修复研究领域的两大问题。镉会借助根部铁转运系统进入水稻。我们的前期研究表明基施螯合铁对土壤和稻米有明显的补铁阻镉效果，然而基施螯合铁对水稻根际铁镉生物有效性及其吸收转运策略尚不清楚。因此，本申请拟以EDDHAFe(III)、EDTANaFe(III)和EDTANa2Fe(II)等3种螯合铁为材料，1)采用离子交换树脂、膜透析和土壤溶液抽提的实验分析方法，结合地球化学模型计算结果，评估螯合铁在水稻根际铁镉元素的生物有效性；2)利用化学分离、电镜、非损伤微测技术及吸收动力学等方法，阐明不同螯合铁对根部吸收铁镉策略的差异；3)通过HPLC-MS和QRT-PCR技术，探索螯合铁对根基木质部转运铁镉形态分子调控机制。本项目将深入研究螯合铁对水稻根部铁镉的吸收和阻隔策略，丰富和完善稻田补铁阻镉理论体系，为螯合铁在我国镉污染稻田土壤的应用提供理论依据。

铁缺乏和镉污染是目前植物营养和植物修复研究领域的两大问题。镉会借助根部铁转运系统进入水稻。我们的前期研究表明基施螯合铁对土壤和稻米有明显的补铁阻镉效果，然而基施螯合铁对水稻根际铁镉生物有效性及其吸收转运策略尚不清楚。本项目以EDDHAFe(III)、EDTANaFe(III)、EDTANa2Fe(II)和柠檬酸铁等螯合铁为研究材料，通过室内水培盆栽实验方法，系统研究基施螯合铁对铁镉从水稻根际营养液-根表铁膜-根部微区组织-根基木质部汁液的选择性吸收转运机制。通过地球化学模型计算结果，评估螯合铁在水稻根际铁镉元素的生物有效性；通过化学分离、非损伤微测技术等方法，阐明不同螯合铁对根部微区吸收铁镉策略的差异；通过QRT-PCR技术，探索螯合铁对根基木质部转运铁镉形态分子调控机制。主要结论如下：（1）营养液中铁、镉和螯合配体的赋存形态与比例主要受螯合常数影响，螯合配体与金属的螯合常数越大，形成的金属螯合物比例越高，解离难度越大，被水稻直接吸收利用的可能性越小。（2）与缺铁处理相比，正常供铁和过量供铁可有效提高水稻根表泌氧速率和铁膜含量，降低水稻根系微区镉离子吸收速率或提高镉离子外排速率。（3）添加铁肥不仅可以有效提高水稻根部和地上部组织铁含量，降低水稻根部和地上部组织镉含量，还可以有效促进木质部对铁的转运，抑制木质部对镉的转运。添加人工螯合铁时，缺铁状态可以促进根部相关铁、镉转运基因（OsHMA2、OsHMA3、OsYSL15、OsNRAMP5和OsIRT2）表达，而丰铁会抑制相关转运基因表达。综上，施加铁肥可有效提高水稻植株铁含量，降低水稻植株镉含量，对水稻有富铁阻镉作用，铁肥可调控水稻对镉的吸收和转运过程。本项目系统研究了螯合铁对水稻根部铁镉的吸收和阻隔策略，丰富和完善稻田补铁阻镉理论体系，为螯合铁在我国镉污染稻田土壤的应用提供理论依据。