Environmental Engineering Reference
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NHL repeat membrane-spanning protein, a metal
transporter and a putative transcription factor
providing cadmium tolerance. Additional can-
didates in the QTL intervals include a putative
homolog of a glutamate cysteine ligase, and a
glutathione-S-transferase. Functional character-
ization of these candidate genes further enhances
our understanding of cadmium metabolism and
transport and phytoremediation capabilities of
Populus
(Induri et al.
2012
).
suppression subtraction hybridization (SSH) and
found 43 genes specifically involved in Cr de-
toxification (Zulfiqar et al.
2011
).
5.4.5
Other Plants
Elsholtzia splendens
is a Cu-tolerant and high
metal-accumulating plant species, thus a likely
candidate for phytoremediation of Cu-contami-
nated soils. Li et al. (
2009
) conducted proteomic
analysis of copper stress response in
E. splendens
roots and leaves by two-dimensional gel electro-
phoresis and found that 45 protein spots were
significantly changed in roots, but only 6 were
changed in leaves. The identified root proteins
were involved in various cellular processes such
as signal transduction, regulation of transcription
and translation, energy metabolism, regulation
of redox homeostasis and cell defence, while the
leaf proteins were mainly degraded fragments of
RuBisCo and antioxidative protein. Lyubenova
et al. (
2009
) showed that when tobacco (
Nico-
tiana tabacum
) plants originating from different
mutants were grown under field conditions with
varying fertilizer application, the uptake of cad-
mium and zinc from soil increased with increas-
ing biomass. Depending on Cd and Zn uptake,
several antioxidant enzymes showed signifi-
cantly different activities. Among them SOD and
CAT were usually elevated; however, isoforms
of GST and several other enzymes were strongly
inhibited.
Zhou et al. (
2009
) revealed the broccoli (
Bras-
sica oleracea
var.
italica
) COQ5 methyltrans-
ferase (
BoCOQ5-2
) gene's involvement in the
ubiquinone biosynthetic pathway. It was found
to promote Se volatilization in both bacteria and
transgenic
Arabidopsis
(
A. thaliana
) plants. Bac-
teria expressing
BoCOQ5-2
showed an over 160-
fold increase in volatile Se compounds under sel-
enate exposure and exhibited enhanced tolerance
to selenate. Transgenic
Arabidopsis
expressing
BoCOQ5-2
volatilized three times more Se than
the vector-only control plants when treated with
selenite and exhibited an increased tolerance to
Se. Ding et al. (
2011
) showed As concentration
in different tissues of maize using a set of re-
5.4.3
Brassica juncea
Brassica juncea
is another promising plant species
that can be used for phytoremediation of heavy
metals.
B. juncea
root proteome was analysed in
response to cadmium exposure, and it was found
that enzymes such as peptide methionine sulf-
oxide reductase and 2-nitropropane dioxygenase
play a role in alternative redox regulation mecha-
nisms, whereas O-acetylserine sulfhydrylase,
glutathione-S-transferase and glutathione-conju-
gate membrane transporter were involved in the
Cd hyperaccumation and tolerance of
B. juncea
(Alvarez et al.
2009
). Another study reported that
under stress condition of Zn, Cd, NaCl or Polyeth-
ylene glycol (PEG), the transcript levels of two
B.
juncea
cation-efflux family proteins, BjCET3 and
BjCET4, substantially increased, suggesting their
roles in stress resistance (Lang et al.
2011
).
5.4.4
Crambe abyssinica
Crambe abyssinica
is a member of Brassicaceae
and an ideal candidate for phytoremediation due
to nonfood, fast-growing, high biomass crop.
Thirty-eight genes encoding glutathione-S-trans-
ferases, antioxidants, sulphur metabolism, heat
shock proteins, metal transporters and enzymes
in the ubiquitination pathway of protein degrada-
tion as well as several unknown novel proteins in-
volved in arsenic metabolism and detoxification
were analysed and isolated successfully (Paulose
et al.
2010
). Zulfiqar et al. (
2011
) reported 72
differentially expressed transcripts after com-
parative Cr exposure analysis using PCR-based
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