As a consequence of industrial development, the environment is increasingly polluted with heavy metals. Plants possess homeostatic mechanisms that allow them to keep correct concentrations of essential metal ions in cellular compartments and to minimize the damaging effects of an excess of nonessential ones. one of their adverse effects on plants is the generation of harmful active oxygen species, leading to oxidative stress. Besides the well-studied antioxidant systems consisting of low-molecular antioxidants and specific enzymes, recent works have begun to highlight the potential role of flavonoids, phenylopropanoids and phenolic acids as effective antioxidants. During heavy metal stress phenolic compounds can act as metal chelators and on the other hand phenolics can directly scavenge molecular species of active oxygen.
Phenolics, especially flavonoids and phenylopropanoids, are oxidized by peroxidase, and act in H₂O₂scavenging, phenolic/ASC/POX system. their antioxidant action resides mainly in their chemical structure. There is some evidence of induction of phenolic metabolism in plants as a response to multiple stresses (including heavy metal stress).