Biotechnological Aspects of Soil Decontamination - Biotechnologies and Biomimetics for Civil Engineering - page 389

Table 17.6 Plant enzymes that have a role in transforming organic compounds (Susarla

et al. 2002 )
Enzymes Plants known to produce enzymatic

activity

Application

Dehalogenases Hybrid poplar (populus spp.), algae

(various spp.), Parrot feather
(Myriophyllum aquaticum)

Dehalogenates chlorinated solvents

Laccase Stonewort (Nitella spp.), parrot-

feather (Myriophyllum aquaticum)

Cleaves aromatic ring after TNT is
reduced to triaminotoluene

Nitrilase Willow (Salix spp.) Cleaves cyanide groups from

aromatic rings

Nitroreductase Hybrid poplar (Populus spp.),

Stonewort (Nitella spp.), parrot
feather (Myriophyllum aquaticum)

Reduces nitro groups on explosives
and other nitroaromatic compounds,
and removes nitrogen from ring
structures

Peroxidase Horseradish (Armoracia rusticana

P.Gaertner, Meyer & Scherb)

Degradation of phenols (mainly used
in wastewater treatment)

Phosphatase Giant duckweed (Spirodela

polyrhiza)

Cleaves phosphate groups from large
organophosphate pesticides

atmosphere (LeDuc et al. 2004 ). The well-known example of genetic manipulation
is the transfer and expression of a modified E. coli Hg 2+ reductase gene (merA9pe)
in transgenic Arabidopsis thaliana plants (Rugh et al. 1996 ). Bacteria possessing
merA are capable of converting highly toxic, Hg 2+ to less toxic elemental Hg.
Thus, expression of merA in transgenic plants helps the removal of elemental Hg
as vapors through natural mechanisms of respiration. Rugh et al. ( 1998 ) also
examined the ability of yellow poplar (Liriondendron tulipifera) tissue cultures
and plantlets to express modified mercuric reductase (merA) gene constructs
(Table 17.4 ).
Phytovolatization potentially offers a low cost alternative for Se removal from
soil and water. During the process of Se volatilization, plants metabolize various
inorganic species of Se [e.g., selenate, selenite, and Se-Met (Met)] into a gaseous
form dimethyl selenide, the major volatile form of Se, is more than 600 times less
toxic than inorganic forms (Evans et al. 1968 ; Berken et al. 2002 ; Neumann et al.
2003 ). Terry et al. ( 1992 ) reported that members of Brassicaceae are capable of
releasing up to 40 g Se/ha/day as various gaseous compounds. Indian mustard
(Brassica juncea) has a high rate of Se accumulation and volatilization, and a fast
growth rate, making it a promising species for Se remediation (Pilon-Smits 2005 ).
Some aquatic plants, such as cattail (Typha latifolia L.), have potential for Se
phytoremediation (Pilon-Smits et al. 1999 ). Volatilization of arsenic (As) as
dimethylarsenite has also been postulated as a resistance mechanism in marine
algae (Salt et al. 1995a , b ). Phytovolatilization has been successful in tritium (3H),
a radioisotope of hydrogen; it is decayed to stable helium with a half-life of about
12 years reported by Dushenkov ( 2003 ). This remediation method has the added
benefits of minimal site disturbance, less erosion, and no need to dispose of
contaminated plant material (Heaton et al. 1998 ). However, phytovolatilization