Environmental Engineering Reference
In-Depth Information
(Robinson et al.
1999
).
FRE1
and
FRE2
genes
isolated from
Saccharomyces cerevisae
(Dancis
et al.
1990
; Georgatsou and Alexandra
1994
) were
cloned in tobacco (Samuelsen et al.
1998
) and the
double mutants (
FRE1
+
FRE2
) were found to be
more tolerant, having high Fe concentration in
leaves than the control and
FRE1
plants. Ferritin
gene from soybean increased Fe accumulation
in
Nicotiana
and rice (Goto et al.
1998
,
1999
).
The gene for the phytoremediation of arsenic,
ʳ-glutamyl cysteine synthetase (
g-ECS
), was iso-
lated from
Escherichia coli
and cloned in
Ara-
bidopsis
with an
actin
promoter. The plant had
moderate tolerance for arsenic. Selenium is an-
other major environmental hazard and is lethal
if amounts go larger than required dose. The
oxidized selenium (selenate or selenite) is less
hazardous than the inorganic ones because the
inorganic selenium (selenide or elemental Se) is
insoluble, and therefore, available in low quanti-
ties for degradation (Eapen and D'Souza
2005
).
Genes such as ATP sulphurylase activates the
assimilation of sulphate and selenium and con-
verts it into adenosine phosphoselenite, which
gets converted to selenite (DeSouza et al.
2000
).
The APS transgenics are more tolerant to Se and
grow at a faster pace than the wild type (Pilon-
Smits et al.
1999
). Various metallothionein (MT)
genes such as
MT2
gene from humans,
MT1
gene
from mice and
MTA
gene from pea has been
transferred to
Nicotiana sp.
and
Arbidopsis sp.
(Misra and Gedamu
1989
; Evans et al.
1992
; Pan
et al.
1994
) for Cd tolerance. MTA gene in
Ara-
bidopsis
augmented copper (Cu) accumulation.
The
CUP1
gene from yeast provided Cd toler-
ance in
Nicotiana
and
B. oleracea
(Hasegawa
et al.
1997
; Thomas et al.
2003
).
YCF1
gene from
yeast provided Cd and Pb tolerance in
Arabidop-
sis
.
NtCBP4
gene in
Nicotiana
showed Ni toler-
ance and Pb accumulation (Arazi et al.
1999
).
Besides metal, genetic engineering also aided
in the phytoremediation of PCBs. Pioneering
work was done by Francova et al. (
2003
), but the
plants were not tested for their capability to me-
tabolize PCB. But then the
bPh
gene from
Bur-
kholderia xenovorans
LB400 was transformed
into
Nicotiana sp
., and the purified enzymes
showed that it was capable of oxidizing 4-chlo-
robiphenyl into 2,3-dihydro-2,3-dihydroxy-4′-
chlorobiphenyl (Mohammadi et al.
2007
).
bphC
gene from
Pseudomonas testosteroni
B-356
when transferred in
Nicotiana sp
. and grown in
the presence of 2,3-dihydroxybiphenyl (0.5 mM),
then one of the transgenic lines exhibited greater
toxic resistance than the wild type (Novakova
et al.
2009
).
More development is required for the success-
ful application of this innovative strategy such as
improvement of metal and PCB-degrading en-
zymes through genetic engineering and studies
on molecular level to bring success regarding the
coordinated expression of different genes respon-
sible for degrading different contaminants.
5.7
Future Research Prospects and
Impact
Presently, trends for phytoremediation technol-
ogy are approaching commercialization. Concur-
rently, short-term advances in phytoremediation
are likely to occur through selection of more ef-
ficient plant varieties and soil amendments and
from optimizing agronomic practices used for
plant cultivation. Major long-term improvements
achieved through identification of potential can-
didate genes from plants and microorganisms
and through understanding of hyperaccumulation
mechanisms in plants, leading to biotransforma-
tion or biodegradation of organics. Additionally,
genetically modified rhizospheric bacteria for
bioremediation and symbiotic association with
plants are required to increase the efficiency of
the future phytoremediation efforts. Transgenic
plants also represent the candidates for the most
efficient and cost-effective phtoremediation.
Transgenic events include modifications in spec-
ificity of trnasporters, overexpression of trans-
porters resulted in increased number of trans-
porters, intracellular ligand production directing
metal targeting into vacuoles without disturbing
cellular processes and biochemical transforma-
tion of metal volatile forms. The biology alone
cannot make phytoremediation work. Multidisci-
plinary research efforts are required that integrate
plant biologists, microbiologists, soil chemists
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