Hyperaccumulators have exceptional phloem translocation capability for heavy metals. This study aims at quantifying the mobility and accumulation of Ni and Co via the phloem in the model hyperaccumulator Noccaea caerulescens. "Phloem loading capability (PLC)," which is calculated by the "Metal content in phloem sap/Metal content in leaves," was introduced to evaluate the metal phloem mobility, while "Phloem mobility value (PMV)" was used for the normalization of PLC, which sets the PLC of Sr as PMV 0 and that of Rb as 100. The results showed that the PMVs of Ni and Co were 63 and 47, respectively. And the phloem mobility of Rb, Ni, Co, and Sr could be graded as highly mobile, mobile, intermediate, and immobile accordingly. The phloem stream can supply up to 19.1% and 16.0% of the total Ni and Co accumulated in the young leaves, respectively, while for Rb and Sr, the phloem contributes to 29% and 1.4% of the total Rb or Sr, indicating phloem contribution of certain metal is directly linked with its mobility. The results of this study raise the importance of phloem translocation on metal accumulation in shoots and provide insights on the metal cycling process in hyperaccumulators.

中文翻译：

---

通过超富集植物 Noccaea caerulescens（十字花科）中的韧皮部量化镍和钴的迁移率和积累。

Hyperaccumulators 对重金属具有特殊的韧皮部易位能力。本研究旨在通过模型超富集植物 Noccaea caerulescens 中的韧皮部量化 Ni 和 Co 的迁移率和积累。引入由“韧皮部汁液中的金属含量/叶片中的金属含量”计算的“韧皮部负载能力（PLC）”来评估金属韧皮部的迁移率，而“韧皮部迁移率值（PMV）”用于标准化PLC 的 PLC，将 Sr 的 PLC 设为 PMV 0，Rb 的 PLC 设为 100。结果表明，Ni 和 Co 的 PMV 分别为 63 和 47。并且Rb、Ni、Co和Sr的韧皮部迁移率可以相应地分级为高迁移率、迁移率、中等迁移率和不动率。韧皮部流最多可提供 19.1% 和 16。在幼叶中分别积累了 0% 的 Ni 和 Co 总量，而对于 Rb 和 Sr，韧皮部贡献了总 Rb 或 Sr 的 29% 和 1.4%，表明某些金属的韧皮部贡献与其迁移率直接相关. 这项研究的结果提高了韧皮部易位对枝条中金属积累的重要性，并提供了对超积累植物中金属循环过程的见解。