Heavy Metal Stress

Environmental contamination by hazardous heavy metals (HMs) is increasing worldwide and poses a serious threat to plant production and human health. Subjection of plants to HM stress lead to a variety of morphological, physiological, and biochemical alterations or even death of plants. The prime drawback to developing HM stress-tolerant plants is the lack of information on in-depth molecular mechanisms and signaling events underlying plant responses to HM toxicity. Plants have array of defense mechanisms to counter the deleterious effects of HM stress. The primary defense mechanisms include the reduced absorption or their sequestration in root cells and secondary mechanisms include the binding of HM ions by phytochelatins, glutathione, and amino acids and modulation of antioxidant defense systems. In recent years, the dual role of reactive oxygen species in HM toxicity because both oxidative damage inducers and signaling molecules has been well-documented and recent developments in molecular biology have facilitated transcriptomics and proteomics studies to identify regulatory genes and signaling pathways implied in HM tolerance in plants. The integration of the current findings will be of extreme significance to dissecting the actual HM stress response network. In this review, we endeavor to describe the specific aspects of the molecular mechanisms of HM stress response and signaling that may contribute for better understanding to produce plants that have traits desirable for imparting HM stress tolerance as well as to provide scientific clues for the development of phytoremediation strategies.