5 Genetically Engineered Plants in Phytoremediation
of Heavy Metals and Organic Pollutants
Phytoremediation is the engineered use of green plants/trees with associated
microbiota for the degradation and detoxification of organic and inorganic pollutants
from the contaminated matrix (soil/water) to safeguard the environment and public
health. Genetically engineered plants were first developed for the phytoremediation
of heavy metals (Misra and Gedamu 1989; Rugh et al. 1996). However, the tobacco
plants were the first genetically engineered plants for the phytoremediation of
organic pollutants (explosives and halogenated organic compounds) (Doty et al.
2000). Genetically engineered plants are developed by introducing the transgene of
interest that are responsible for the metabolism of xenobiotic compounds and offer
increased resistance to pollutants (Abhilash et al. 2009). Due to the increased
capacity to accumulate toxic metals from contaminated matrix, plants are chiefly
preferred for the phytoremediation of heavy metals-contaminated sites. After
phytoremediation, the aboveground harvestable plant biomass is safely disposed of
or utilized to recover the valuable metals for future use (Salt et al. 1998). Genetically
engineered plants used for the phytoremediation of environmental contaminants are
listed in Table 1.2.
Phytoremediation has several advantages over microbial bioremediation approaches
such as high biomass of the remediating plants with less nutrient requirements, which
prevent migration of pollutants from one place to another and greater acceptance
among public (Alkorta et al. 2004). The best known metal hyperaccumulating plant
is alpine pennycress, Thlaspi caerulescens, which hyperaccumulates Zn
2+
, Cd
2+
, and
Ni
2+ from contaminated matrix (Milner and Kochian 2008; Baker et al. 2000). Members of Brassicaceae, Alyssum sp. (a serpentine-endemic shrub), Astragalus racemosus,
Leguminosae milkvetch, and Indian mustard Brassica juncea, are known to accumulate
high concentration of heavy metals from contaminated environment (Reeves and Baker
2000). Recently, Asian stonecrop, Sedum alfredii of Crassulaceae, has gained more
attention to researchers as it hyperaccumulates Pb
2+ and Cd
2+ and Zn
2+ with more than
2% of shoot weight (Yang et al. 2003; Lu et al. 2008; Deng et al. 2008).
Further, the genetically engineered, fast-growing, and high-biomass-producing
metal hyperaccumulators with required genetic traits have been proved to be the
suitable candidates for the phytoremediation of contaminants and include shrub
tobacco Nicotiana glaucum, B. juncea, yellow poplar Liriodendron tulipifera, and
sunflower Helianthus annuus (Eapen and D’Souza 2005). Several publications have
reported the potential of phytoremediation to restore the polychlorophenolcontaminated soil/water (Newman and Reynolds 2004). Different plant-based remediation approaches are known including the rhizosphere biodegradation of
chlorophenols inside the plant tissues (Van 2009). de Araujo et al. (2002) showed
that Agrobacterium rhizogenes-transformed roots removed up to 90% phenolics,
including phenol, 2-chlorophenol (2-CP), 2,6-dichlorophenol (2,6-DCP), and 2,4,6TCP, from culture medium within 120 h. Sandermann (1994) studied the plant
1 Genetically Modified Organisms (GMOs) and Their Potential in. . .
9
of Heavy Metals and Organic Pollutants
Phytoremediation is the engineered use of green plants/trees with associated
microbiota for the degradation and detoxification of organic and inorganic pollutants
from the contaminated matrix (soil/water) to safeguard the environment and public
health. Genetically engineered plants were first developed for the phytoremediation
of heavy metals (Misra and Gedamu 1989; Rugh et al. 1996). However, the tobacco
plants were the first genetically engineered plants for the phytoremediation of
organic pollutants (explosives and halogenated organic compounds) (Doty et al.
2000). Genetically engineered plants are developed by introducing the transgene of
interest that are responsible for the metabolism of xenobiotic compounds and offer
increased resistance to pollutants (Abhilash et al. 2009). Due to the increased
capacity to accumulate toxic metals from contaminated matrix, plants are chiefly
preferred for the phytoremediation of heavy metals-contaminated sites. After
phytoremediation, the aboveground harvestable plant biomass is safely disposed of
or utilized to recover the valuable metals for future use (Salt et al. 1998). Genetically
engineered plants used for the phytoremediation of environmental contaminants are
listed in Table 1.2.
Phytoremediation has several advantages over microbial bioremediation approaches
such as high biomass of the remediating plants with less nutrient requirements, which
prevent migration of pollutants from one place to another and greater acceptance
among public (Alkorta et al. 2004). The best known metal hyperaccumulating plant
is alpine pennycress, Thlaspi caerulescens, which hyperaccumulates Zn
2+
, Cd
2+
, and
Ni
2+ from contaminated matrix (Milner and Kochian 2008; Baker et al. 2000). Members of Brassicaceae, Alyssum sp. (a serpentine-endemic shrub), Astragalus racemosus,
Leguminosae milkvetch, and Indian mustard Brassica juncea, are known to accumulate
high concentration of heavy metals from contaminated environment (Reeves and Baker
2000). Recently, Asian stonecrop, Sedum alfredii of Crassulaceae, has gained more
attention to researchers as it hyperaccumulates Pb
2+ and Cd
2+ and Zn
2+ with more than
2% of shoot weight (Yang et al. 2003; Lu et al. 2008; Deng et al. 2008).
Further, the genetically engineered, fast-growing, and high-biomass-producing
metal hyperaccumulators with required genetic traits have been proved to be the
suitable candidates for the phytoremediation of contaminants and include shrub
tobacco Nicotiana glaucum, B. juncea, yellow poplar Liriodendron tulipifera, and
sunflower Helianthus annuus (Eapen and D’Souza 2005). Several publications have
reported the potential of phytoremediation to restore the polychlorophenolcontaminated soil/water (Newman and Reynolds 2004). Different plant-based remediation approaches are known including the rhizosphere biodegradation of
chlorophenols inside the plant tissues (Van 2009). de Araujo et al. (2002) showed
that Agrobacterium rhizogenes-transformed roots removed up to 90% phenolics,
including phenol, 2-chlorophenol (2-CP), 2,6-dichlorophenol (2,6-DCP), and 2,4,6TCP, from culture medium within 120 h. Sandermann (1994) studied the plant
1 Genetically Modified Organisms (GMOs) and Their Potential in. . .
9