Hairy Roots: A Promising Tool for Phytoremediation

Environmental pollution caused by natural processes or anthropogenic activities is a major global problem. Although several physical and chemical strategies have been used for environmental remediation, these methods are expensive and associated with certain limitations. Phytoremediation is an alternative, biological approach where different plant species are used for the removal of pollutants from the environment or for converting toxic molecules to non toxic forms. Both organic and inorganic compounds of various types are the targets of phytoremediation. The technique is cheaper than other established methods and has several advantages like soil stabilization, production of biofuels, non invasiveness etc. Plants readily absorb certain compounds, otherwise considered contaminants, through the root system and utilize for their normal growth and development. Hairy roots of plants are among the several experimental systems which have been employed to improve the efficiency of phytoremediation. Hairy root disease, characterized by a massive production of adventitious roots with numerous root hairs at the wound site, is caused by Agrobacterium rhizogenes, a gram negative soil bacterium. The bacterium transfers a segment (the transferred DNA or T-DNA) of its root inducing (Ri) megaplasmid into the plant genome, modifying the normal hormonal metabolism of the plant; this hormonal imbalance induces the formation of hairy roots at the site of infection. Apart from being suitable for the production of a wide array of valuable secondary metabolites, hairy roots possess tremendous potential for phytoremediation. Hairy roots of different plant species have been investigated for the accumulation and biodegradation of hazardous compounds. The present review summarizes the role of plant hairy roots in phytoremediation research.