Role of root exudates in metal acquisition and tolerance

•Strategy I plants secrete riboflavins or phenolics to facilitate Fe acquisition.•Strategy II plants secrete phytosiderophores to acquire Fe.•Exudation of organic acids is important for heavy metal detoxification.

Plants acquire mineral nutrients mostly through the rhizosphere; they secrete a large number of metabolites into the rhizosphere to regulate nutrient availability and to detoxify undesirable metal pollutants in soils. The secreted metabolites are inorganic ions, gaseous molecules, and mainly carbon-based compounds. This review focuses on the mechanisms and regulation of low-molecular-weight organic-compound exudation in terms of metal acquisition. We summarize findings on riboflavin/phenolic-facilitated and phytosiderophore-facilitated iron acquisition and discuss recent studies of the functions and secretion mechanisms of low-molecular-weight organic acids in heavy-metal detoxification.