ABSTRACT
Increasing industrialization and urbanization have led to unprecedented bioaccumulation of heavy metals in the environment, causing serious threats to all living organisms, including plants. At toxic levels, heavy metals can stimulate excessive generation of reactive oxygen species (ROS), which impose serious morphological, metabolic, and physiological anomalies in plants. In order to deal with heavy metal–induced oxidative stress, plants have adopted a few strategies, including a sophisticated antioxidant defense system and a glyoxalase system to scavenge the ROS and methylglyoxal (MG), respectively. Glutathione plays a very important role in both these defense systems by direct and indirect control of levels of ROS and MG, thus protecting the plants from heavy metal stress. In addition to this, plants produce certain cellular biomolecules such as phytochelatins (PCs), metallothioneins (MTs), proline, organic acids, amino acids, and so on , which serve to form ligand–metal complexes followed by the removal of metals from the sensitive sites through vacuolar sequestration. Another important feature of plants’ defense system is the symbiotic association with mycorrhizal fungi that can effectively immobilize heavy metals and reduce their uptake by plants. The present chapter discusses in detail the different adaptation strategies adopted by plants to ameliorate heavy metal stress. Here, we also emphasize the role of different phytoremediation strategies that can act as important tools in mitigating heavy metal stress in plants in the near future.
