镉(Cadmium, Cd)是一种毒性极强的重金属元素，土壤中的镉通过植物根系进 入植物体后不仅会严重抑制植物的生长发育，还会通过食物链在人体内富集威胁人 类健康。水稻(Oryza sativa L.)是我国主要粮食作物之一，其根系对镉的吸收能力 较强，稻田镉污染极易造成稻米镉含量超标。本研究试图利用植物内生促生菌和IAA 促进镉胁迫下水稻的生长，并降低水稻对镉的吸收转运，从而达到提高水稻产 量和降低稻米中镉含量的目的，为 Cd 污染土壤中水稻的安全生产提供调控途径。

本实验以扬稻6号(籼稻，Oryza sativa L. indica)和本实验室分离、保存的植 物内生促生菌为材料，通过促生实验筛选出内生促生菌和外源 IAA 浓度。之后再以 宁粳7号(粳稻，Oryza sativa L. japonica)和扬稻6号为材料，研究水培和土培条 件下内生促生菌 Bc09 和 IAA 对水稻的生长及镉吸收转运的影响。主要研究结果如 下:

1、促生实验结果表明，内生促生菌 Bc09(Pseudomonas grimontii)对水稻幼苗 具有明显的促生效果，能显著减少水稻根部、地上部镉浓度和镉转运系数。1 μmol L-1 IAA可以显著促进水稻幼苗的生长，降低水稻地上部的镉浓度和镉转运系数。

2、水培条件下，20 μmol L-1镉胁迫明显抑制了宁粳7号和扬稻6号的生长，降 低了两个水稻品种的株高、根长和生物量，总根长(TRL)、根表面积(RSA)、根 体积(RV)等根系形态指标也显著降低，且镉对扬稻 6 号的毒害作用大于宁粳 7 号。 接种 Bc09 和 IAA 处理都能缓解镉对两个水稻品种生长的抑制，显著提高水稻的株 高和生物量，明显改善水稻的根系形态，而且接种 Bc09 对水稻的促生效果比 IAA处理更好，两种处理对扬稻 6 号的促生效果更好。接种 Bc09 和 IAA 处理都能降低 水稻幼苗的镉含量，接种 Bc09 能降低水稻的根部、地上部镉浓度和镉转运系数，而IAA 处理只能降低其地上部镉浓度和镉转运系数。这说明 Bc09 能够降低水稻根系对 镉的吸收及其向地上部的转运，IAA 只能降低水稻根部镉向地上部的转运。

3、土培实验中土壤的镉含量为 14.43 ± 0.95 mg kg-1。结果显示，内生促生菌Bc09 和 IAA 处理都能促进镉污染土壤中两个水稻品种的生长，与单一镉处理相比，

接种 Bc09 和 IAA 处理都能一定程度提高水稻的株高、地上部干重、单穗实粒数和 千粒重，且在扬稻 6 号中增加幅度更大，接种 Bc09 比 IAA 处理的促生作用更明显。 接种 Bc09 能降低两个水稻品种根、秸秆、叶片和籽粒中镉浓度，且扬稻 6 号籽粒中 镉浓度的降低幅度大于宁粳 7 号，IAA 处理能降低扬稻 6 号秸秆、叶片和籽粒中镉 浓度，说明 Bc09 能降低水稻对镉的吸收和转运，IAA 能降低水稻对镉的转运，这与 水培结果一致。Bc09 能够增加水稻根系对 P 和 K 的吸收转运，进而增加籽粒中 P 和

K 含量，从而提高镉胁迫下水稻的产量。Bc09 处理还能够显著降低镉污染土壤的生 物有效态镉含量，进而有效地降低了水稻根系对镉的吸收转运，最终降低籽粒中的镉含量。

4、接种 Bc09 和 IAA 处理都能显著增加镉胁迫下两个水稻品种的脯氨酸含量， 减少 MDA 含量，还能提高水稻的内源 IAA 含量、根系活力和叶绿素含量。另外，Bc09 和 IAA 处理也能显著提高两个水稻品种对 Fe、Mn、Ca 和 Mg 等营养元素的吸 收，这不仅能够促进镉胁迫下水稻的生长，还能增强其与 Cd 竞争质膜上的吸收转运 位点的能力，最终降低水稻对 Cd 的吸收转运。

Cadmium (Cd) is a very toxic heavy metal element. Cd in soil enters into plants through plant roots, which not only seriously inhibits the growth and development of plants, but also accumulates in human body through food chain, threatening human health. Rice (Oryza sativa L.) is one of the main food crops in China. Its root system has a strong ability to absorb cadmium. Cd pollution in paddy field can easily lead to excessive Cd content in rice. In this study, plant growth-promoting bacteria and IAA were used to promote the growth of rice under Cd stress, and reduce the uptake and transport of Cd in rice, so as to improve the yield of rice and reduce the Cd content in grains, and provide a regulatory way for the safe production of rice in Cd contaminated soil.

In this experiment, Yangdao 6 (Oryza sativa L. indica) and the plant growth promoting bacteria isolated and preserved in our laboratory were used as materials. The Cd-tolerant endophytic growth promoting bacteria and the concentration of exogenous IAA were screened through the growth promoting experiment. Then, Ninggeng 7 (Oryza sativa L.japonica) and Yangdao 6 were used as materials to study the effects of Cd-tolerant endophytic growth promoting bacteria Bc09 and IAA on rice growth and Cd uptake and transport under hydroponic and soil culture conditions. The main findings are as follows:

1. The results of growth promotion experiment showed that endophytic growth promoting bacteria Bc09 (Pseudomonas grimontii) had obvious growth promoting effect on rice seedling, which could significantly reduce the Cd concentration in rice root and shoot and Cd translocation factors. 1 μmol L-1 IAA could not only significantly promote the growth of rice seedling, but also reduce the Cd concentration in rice shoot and Cd translocation factors.

2. Under hydroponic conditions, 20 μmol L-1 Cd stress significantly inhibited the growth of Ninggeng 7 and Yangdao 6, reduced the plant height, root length and biomass of the two rice cultivars, and significantly reduced the root morphology indicators such as total root length (TRL), root surface area (RSA) and root volume (RV). Moreover, the toxic effect of Cd on Yangdao 6 was greater than that on Ninggeng 7. The results showed that both Bc09 inoculation and IAA treatment could alleviate the inhibition of Cd on the growth of two rice cultivars, significantly improve the plant height and biomass of rice, and improve the root morphology of rice. Moreover, the growth promoting effect of Bc09 inoculation on rice was better than that of IAA treatment, and the growth promoting effect of two treatments on Yangdao 6 was better. Inoculation with Bc09 can reduce the Cd concentration in the roots and shoots and translocation factors of rice, while IAA treatment can only reduce the Cd concentration in the shoots and translocation factors. It shows that Bc09 reduces the absorption of Cd from rice roots and its transport to shoots, while IAA reduces the transport of Cd from rice roots to shoots.

3. The content of Cd in soil was 14.43 ± 0.95 mg kg-1. The results showed that both Bc09 and IAA treatment could promote the growth of two rice cultivars in Cd- contaminated soil, Compared with single Cd treatment, both Bc09 and IAA treatment could increase plant height, dry weight of shoot, number of grains per panicle, thousand-grain weight to some extent, and the increase was greater in Yangdao 6. The growth promoting effect of Bc09 inoculation was more obvious than that of IAA treatment. Inoculation with Bc09 could reduce the Cd concentration in roots, straws, leaves and grains of two rice cultivars, and the decrease of Cd concentration in grains of Yangdao 6 was greater than that of Ninggeng 7. IAA treatment could reduce the Cd concentration in straws, leaves and grains of Yangdao 6, indicating that Bc09 could reduce the absorption and transport of Cd in rice, and IAA could reduce the transport of Cd, which is consistent with the result of hydroponic conditions. Bc09 could increase the uptake and transport of P and K by rice roots, and then increase the content of P and K in grains, so as to improve the yield of rice under Cd stress. Bc09 could also significantly reduce the bioavailable Cd content in Cd- contaminated soil, thus effectively reducing the uptake and transport of Cd by rice roots, and ultimately reducing the Cd content in grains.

4. Both Bc09 inoculation and IAA treatment could significantly increase the proline content and decrease the MDA content of the two rice cultivars under Cd stress, and could also improve the endogenous IAA content, root activity and chlorophyll content of rice. In addition, Bc09 inoculation and IAA treatment also significantly increased the uptake of Fe, Mn, Ca and Mg in two rice cultivars, which not only promoted the growth of rice under Cd stress, but also enhanced its ability to compete with Cd for the absorption and transport sites on the plasma membrane, and ultimately reduced the absorption and transport of Cd in rice.