Changes caused by heavy metals in micronutrient content and antioxidant system of forage grasses used for phytoremediation: an overview

An increase in the content of heavy metals in the environment causes many socio-environmental problems, and phytoremediation is a tool to reduce the environmental impact caused by these elements, with prospects for the use of forage grasses. This group of plants features characteristics for the environment-decontamination process, but further studies are necessary about the damages caused by heavy metals on the uptake of cationic micronutrients and on the antioxidant system, which are essential processes for the growth of plants in contaminated sites. Exposure of forage grasses to heavy metals results in a lower content of Mn in the shoots of almost all plants, but the contents of Cu, Fe, and Zn vary according to heavy metal and forage grass. Activities of enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and guaiacol peroxidase (GPX) usually increase to reduce the oxidative stress induced by heavy metals, but when the content of any of these metals is high, enzymatic activity is decreased. Scale of toxicity of heavy metals to forage grasses can be described as: Pb approximate to Cr > Cd approximate to As > Zn approximate to Cu approximate to Ni > Mn.