Abstract: Hyperaccumulators are a group of specialized plants that absorb large amounts of heavy metals and store most of them in their aboveground parts. These plants are rich in organic ligands, such as nicotianamine and histidine, which can combine with metals to form metal-ligand complexes. At present, the studies on nickel and zinc organic ligands in plants are relatively sufficient. Therefore, this paper focuses on the interaction between organic ligands and heavy metals during root transport and detoxification, xylem transport and leaf detoxification processes, the molecular mechanism of organic ligand synthesis in hyperaccumulators, as well as methods for detection of organic ligands and metal complexes. To sum up, organic ligands may promote the migration of Ni and Zn in the symplasts of hyperaccumulators and alleviate the cytotoxicity of excess Ni and Zn. In the process of xylem transport, nickel and zinc mainly occur by hydrated ions, but the role of organic ligands is relatively weak in this process. Nickel and zinc mainly combine with organic acid for leaf detoxification. Since most of the findings come from a limited number of hyperaccumulators and organic ligands, it is necessary to combine metabonomics and transcriptomics to study the characteristics and molecular mechanisms about detoxification of organic ligands in more species of hyperaccumulators in the future, so as to provide theoretical basis for clarifying the relevant mechanisms of selective hyperaccumulation of heavy metals in plants and for the application of hyperaccumulators in phytoextraction.

Key words: ligands, zinc, nickel, hyperaccumulator