Transgenic approaches for phytoextraction of heavy metals

Abstract

Large areas of developed as well as developing countries have been contaminated with high concentration of heavy metals resulting from emissions from combustion plants, oil, mining and other industrial processes, incinerators, and military and waste practices. These heavy metals are a health hazard to all forms of life and pose serious danger to public health by entering the food chain or by leaching into drinking water, besides having a negative impact on ecosystems and other natural resources. Phytoextraction refers to the removal of contaminants from soils by plants and their transportation and concentration in the harvestable parts. Several plant species are known that flourish in the presence of high concentration of metals in the soil and even hyperaccumulate them in their shoots. However, most of the metal-accumulating plants exhibit metal selectivity, show sluggish growth, produce little biomass, and cannot be utilized for remediation other than in their natural habitats. An interesting alternative can be the modification of a rapidly growing non-accumulator plant to achieve some of the features of the hyperaccumulators. Although conventional breeding approaches coupled with suitable agronomic practices can go a long way in enhancing the phytoextraction capacity, several anatomical constraints severely restrict sexual compatibility between taxa and pose serious limitations in developing hybrids with increased phytoextraction capability. Recombinant DNA technology has opened new gateways in phytoremediation technology by offering the opportunity for direct gene transfer that would overcome sexual incompatibility, if present. This approach of the development of transgenics having increased uptake, accumulation, and tolerance can be considered as a good alternative. The present work discusses various approaches used to develop transgenic plants having increased phytoextraction capacity and the future of transgenic technology for effective remediation of heavy metal-contaminated soils.