水稻根系分泌物对根表铁膜固定镉的影响机制研究

The uptake of cadmium (Cd) by rice (Oryza Sativa L.) plant mainly occurs on its root surface, and the bioavailability of Cd in rhizospheric soil is directly affected by the binding properties of Cd with the iron plaque. The formation of iron plaque on the root surface and the immobilization of Cd by iron plaque were greatly affected by the root exudates from the rice plant, while the mechanism is still unclear. Therefore, the root-soil interface of Cd-contaminated paddy soil would be selected as the research object to investigate the binding properties of Cd with the iron plaque from the aspect of rice root exudates, thus to explore the effects of root exudates on Cd immobilization by iron plaque. In this research, the compositions and contents of root exudates under the Cd stress will be determined; Cd speciation in rhizospheric soils affected by root exudates will be analyzed; the contents and mineral compositions of iron plaque formed on rice root surface treated with or without root exudates will be characterized; and the speciation and the binding properties of Cd immobilized by iron plaque in the presence of rice root exudates will be identified. This research is expected to elucidate the effects of rice root exudates on the mechanism of Cd immobilization by iron plaque. It will provide the scientific basis for the development of barrier techniques to Cd uptake by rice roots in Cd-contaminated paddy fields, and it is also of great significance to the secure agricultural production and ecological health.

水稻对镉的吸收主要发生在根表，根表铁膜与镉的结合特征直接影响镉的生物有效性。根系分泌物影响铁膜的形成以及铁膜对镉的固定，但其机制尚未明确。本项目拟以镉污染稻田根-土界面为研究对象，以根系分泌物为切入点，以根表铁膜与镉的结合状态为核心，研究水稻根系分泌物对根表铁膜固定镉的影响机制。明确镉胁迫下水稻根系分泌物的组成和含量，以及不同根系分泌物组分对镉形态转化的影响；表征根系分泌物作用下水稻根表铁膜的数量和矿物组成，揭示不同根系分泌物组分对根表铁膜形成的影响机制；进一步研究根系分泌物作用下铁膜与镉的结合状态以及根际土壤镉形态等特征，阐明根系分泌物对根表铁膜固定镉的影响机制。本研究可为镉污染稻田中水稻根表对镉吸收的阻控技术开发提供科学依据，对农业安全生产和生态健康具有重要的意义。

水稻对镉的吸收主要发生在根表，而铁膜的数量和形态是影响水稻根表镉吸收的关键因素。根系分泌物影响铁膜的形成以及铁膜对镉的固定，但其机制尚未明确。本项目通过溶液培养、化学分析等手段，探讨了Cd胁迫下水稻根分泌物组成特征和低分子量有机酸对水稻吸收Cd的影响，同时开展了纳米氧化铁及外源亚铁添加对水稻铁膜形成及其影响水稻吸收Cd的机制研究。⑴外源Cd胁迫下，水稻根系分泌物的主要有低分子量有机酸和氨基酸组成：检测出来8种低分子量有机酸，其中酒石酸、琥珀酸和柠檬酸等有机酸的浓度较高；检测出来17种游离氨基酸，其中精氨酸的浓度最高。⑵添加草酸和酒石酸可缓解Cd对水稻的毒性。添加草酸和酒石酸提高了水稻根系中Cd的含量，但是显著降低了水稻地上部Cd的含量，并降低了Cd由根部向地上部的转运。⑶Fe2O3NPs的添加，缓解了Cd胁迫对水稻幼苗生长的负面影响，调节了水稻植株内的POD、SOD和CAT活性，并维持了植物抗氧化防御系统的平衡。施用Fe2O3NPs通过诱导铁膜的生长、调控Fe/Cd转运基因的表达，从而控制着水稻根系对Cd的吸收和转运。施用Fe2O3NPs后，水稻植株根部和地上部Cd浓度分别显著降低21.2%和42.8%；Cd+FeNPs处理的Cd的转移系数从Cd处理的0.14显著降低至0.099。⑷添加Fe(II)处理后，显著提高了铁膜的含量，同时显著降低了根表铁膜的Cd含量。具体来说，与CK处理组相比，Fe(II)、Cd1+Fe(II)、Cd2+Fe(II)和Cd5+Fe(II)处理中的铁膜含量分别增加了4.81、3.31、5.96和6.35倍。外源亚铁的添加减低了水稻对Cd的吸收：Cd1+Fe(II)和Cd5+Fe(II)处理中地上部Cd的含量比与Cd1和Cd5处理分别降低了10.0%和33.0%。本研究可为镉污染稻田中水稻根表对镉吸收的阻控技术开发提供科学依据，对农业安全生产和生态健康具有重要的意义。