Heavy Metal Phytoremediation by Bioenergy Plants and Associated Tolerance Mechanisms

Bioenergy plants that are better adapted to metal-contaminated lands can be used for phytoremediation purposes and also can be additionally used to produce biofuels such as bioethanol, biodiesel, and biogas. These plants offer the dual advantages of phytoremediation and bioenergy production and majority of them are heavy metal accumulators sequestering exceptionally high amount of the absorbed metals into their biomass. Although diverse heavy metal stress tolerance mechanisms are observed in plants, mainly the metals are effectively immobilized in the roots or if transported to shoots, metal ions are avoided from the sensitive sites and thereby protect the plants from toxicity of the metals. Owing to the fact that most of the reviews published earlier have been focusing on the production of biofuels from the biomass, mostly emphasizing on edible plants, in the present review the heavy metals immobilization mechanisms operational in non-edible bioenergy plants having phytoremediation potential is highlighted. Growing energy plants in heavy metal-contaminated lands is a means of sustainable utilization of the contaminated lands and it also prevents the entry of heavy metals into the food chain. This review, therefore, gives an overview of heavy metal accumulating non-edible bioenergy plants, benefits of using bioenergy plants for phytoremediation, metal tolerance mechanisms in these accumulators, and future perspectives.