Low-molecular weight organic acids and peptides involved in the long-distance transport of trace metals

Higher plants evolved mechanisms of uptake, distribution and accumulation of trace metals essential for the proper functioning of the organism (e.g., copper, zinc). Non-essential metals (e.g., cadmium, arsenic, lead) can also enter plant cells using the routes dedicated to the essential ones, because of the shared similar chemical and physical properties. Generally, trace elements are very reactive, able to generate reactive oxygen species and to interact or bind various organic ligands composed of C, H, O, N, P or S. Thus, after entering to the cells, metals are transported and sequestered mainly in a complex form, bound with amino acids, organic acids, peptides or specific metal-binding ligands. Considering diverse properties (e.g., pH value, abundancy of ions, redox state) characterizing cells, tissues and phloem or xylem sap, plants use various ligands to form stable complexes in different conditions. This literature review aims to provide a comprehensive overview on the role of low-molecular weight acids and peptides in trace metals translocation.