Transgenic Approaches to Enhance Phytoremediation of Heavy Metal-Polluted Soils
Bioremediation using living plant species, referred to as phytoremediation, covers several different strategies, of which phytoremediation of metal-contaminated soils employs phytoextraction, rhizofiltration, phytostabilization, and phytovolatilization. A
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Transgenic Approaches to Enhance Phytoremediation of Heavy Metal-Polluted Soils Pavel Kotrba
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Introduction
Contamination of soils and sediments with toxic heavy metals contributes to serious environmental, economic, and health problems. Plants are predominant organisms in most ecosystems and have the natural ability to take up toxic metals along with micronutrients (Sarwar et al. 2010; Kabata-Pendias 2011). A promising and relatively new technology, referred to as phytoremediation, offers benefits of affordable and environmentally sustainable in situ bioremediation method (Pilon-Smits 2005; Macek et al. 2008; Doty 2008; Kotrba et al. 2009; Aken et al. 2010; Bhargava et al. 2012; Rajkumar et al. 2012). The phytoremediation approaches considered particularly suitable for reclamation of metal-polluted soils are phytoextraction and phytovolatilization. Phytoextraction aims at use of metal-accumulating plants that concentrate the pollutant in aboveground harvestable parts. Phytovolatilization is a process by which plants allow the accumulated pollutant to evaporate through their leaf surface when converted in planta to volatile forms. There are also other tactics relevant to phytoremediation of inorganic xenobiotics. In phytostabilization, plants are employed to prevent migration of contaminants to sites where they may pose a danger, and in rhizofiltration plant roots are used to absorb, concentrate, and/or precipitate pollutants from contaminated effluents. Soils with abnormally high concentrations of some of the elements vary widely in their effects on different plant species. Some plants, including several metallophyte crops such as Indian mustard (Brassica juncea) or sunflower (Helianthus annuus),
This chapter is dedicated to the memory of my colleague, Professor Martina Mackova´ (1965–2012). P. Kotrba (*) Department of Biochemistry and Microbiology, Institute of Chemical Technology, Prague, Technicka´ 5, Prague 166 28, Czech Republic e-mail: [email protected] D.K. Gupta (ed.), Plant-Based Remediation Processes, Soil Biology 35, DOI 10.1007/978-3-642-35564-6_12, # Springer-Verlag Berlin Heidelberg 2013
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have an inherent ability to accumulate high concentrations of metals in the aboveground biomass (Kabata-Pendias 2011). Of particular interest are species, referred to as hyperaccumulators, that are able to accumulate in their shoots more than two and up to four orders of magnitude higher concentrations of heavy metals than other adjacent plants (Brooks 1998; Reeves 2006; Verbruggen et al. 2009; Kra¨mer 2010). The term hyperaccumulation was coined by Jaffre et al. (1976) who reported an extreme phenotype of Sebertia acumunata. This species produces latex containing up to 26 g Ni kg1, probably the most extreme metal concentration reported in plants to date. Currently, the accepted concentration criterions in shoot tissues of hyperaccumulators on a dry-weight basis are >0.1 wt% for most metals, except, for example, for zinc (>1 wt%), cadmium (>0.01 wt%), or gold (>0.0001 wt%) (Baker et
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