Manganese (Mn) transporter OsNRAMP5 was widely reported to regulate cadmium (Cd) uptake in rice. However, the relationship between OsNRAMP5 expression level and Cd accumulation, impacts of external ion activities on OsNRAMP5 expression level and Cd accumulation are still unclear. Investigations of the relationship between OsNRAMP5 expression level and Cd accumulation in three indica rice genotypes were conducted under various external Mn²⁺ activities ranging from Mn deficiency to toxicity in EGTA-buffered nutrient solution. Results in this work indicated that OsNRAMP5 expression level in roots significantly up-regulated at Mn phytotoxicity compared to that at Mn deficiency, which may stimulate by the increasing uptake of Mn. Our work also demonstrated that root Cd concentration of all the tested rice decreased notably when external Mn²⁺ activity reached the level of toxicity. This may explain by the increasing competition between the excess Mn²⁺ and Cd²⁺ as well as the disorder of element absorption caused by root damage at Mn toxicity. Our work also revealed that the relationship between OsNRAMP5 expression level in roots and Cd accumulation in roots was insignificant for all the tested genotypes. Besides, OsNRAMP5 expression level in roots seemed more related to root Mn accumulation. The fact that function of OsNRAMP5 mainly focuses on Mn uptake, together with the fact that many transporter genes involved in Cd uptake might result in the insignificant correlation between OsNRAMP5 expression level and Cd accumulation in roots. At last, multi-level regulating and processing of the process from gene expression to protein translation might account for the inconsistent relationship between root OsNRAMP5 expression level and Cd accumulation in roots.

锰（Mn）转运蛋白OsNRAMP5可以调节水稻中镉（Cd）的吸收。然而，OsNRAMP5表达水平与Cd积累之间的关系，外部离子活性对OsNRAMP5表达水平和Cd积累的影响尚不清楚。之间的关系的调查OsNRAMP5在三个表达水平和Cd积累籼稻稻基因型下各种外部进行的Mn ²⁺活动，从缺锰在EGTA缓冲营养液的毒性。这项工作的结果表明，OsNRAMP5与Mn缺乏时相比，Mn的植物毒性显着上调了根的表达水平，这可能通过增加Mn的吸收来刺激。我们的工作还表明，当外部Mn ²⁺活性达到毒性水平时，所有受试水稻的根Cd浓度均显着降低。这可以解释为过量的Mn ²⁺和Cd ²⁺之间的竞争加剧，以及由于Mn毒性时根部损伤引起的元素吸收障碍。我们的工作还表明，对于所有测试的基因型，根中OsNRAMP5表达水平与根中Cd积累之间的关系均无关紧要。此外，OsNRAMP5根中的表达水平似乎与根中Mn的积累有关。OsNRAMP5的功能主要集中在Mn吸收这一事实，以及许多参与Cd吸收的转运蛋白基因可能导致OsNRAMP5表达水平与根中Cd积累之间的相关性很小。最后，从基因表达到蛋白质翻译的过程的多级调节和处理可能解释了根OsNRAMP5表达水平与根中Cd积累之间的不一致关系。