Environmental Engineering Reference
In-Depth Information
soil remediation technique, and has been exten-
sively used in immobilization of heavy metals in
contaminated soils (Kumpiene et al.
2008
). The
application of silicon, H
2
O
2
, and iron are also
discussed.
the ability to inhibit nicotinamide adenine di-
nucleotide phosphate (NADPH) oxidation and
centered free radical generation (Cakmak
2000
).
Aly and Soliman (
1998
) studied the effect of
SA on iron uptake in soybean genotypes. They
found that SA was effective in correcting iron
chlorosis in soybean genotypes grown in calcar-
eous soils. Al-Hakimi and Hamada (
2001
) also
observed similar effects of SA in the Na, K, Ca,
and Mg content of wheat plants grown under sa-
linity, whereas in maize, exogenous SA applica-
tions inhibited Na
+
accumulation, but stimulated
N, P, K, Mg, Fe, Mn, and Cu uptake (Gunes et
al
.
2007
). According to El-Tayeb (
2005
), an in-
crease in concentrations of K and Ca in plants
under salt stress could ameliorate the deleterious
effects of salinity on growth and yield. Therefore,
alteration of mineral uptake from SA applications
may be one mechanism for the alleviation of salt/
metal stress (Karlidag et al.
2009
).
Recently, Singh and Chaturvedi (
2012
) ob-
served that SA at concentration of 10 ﾵM was
inducing nitrate reductase (NR) activity. On the
contrary, Fariduddin et al
.
(
2003
) reported low
concentrations of SA increased NR activity,
while higher concentrations were inhibitory in
B.
juncea
. The concentration of SA might play an
active role in such a regulation, where the lower
concentration favored an increase in the NR pro-
tein and higher quantity of SA decreased it by
affecting the balance between its synthesis/acti-
vation and degradation/inactivation. The increase
in the content of nitrates and thereby activity of
NR due to exogenous SA treatment under normal
growth conditions was also reported by Hayat
et al. (
2012
). Incorporation of NH
4
+
into gluta-
mate is brought about by successive and highly
regulated actions of nitrogen metabolism en-
zymes (glutamine synthetase, GS; glutamate syn-
thase, GOGAT; and glutamate dehydrogenase,
GDH). SA, due to its action at transcriptional
and/or translational levels, might have acceler-
ated the synthesis and thereby activity of GDH,
GS, and GOGAT (Hayat et al.
2010
). Hence, it
might be possible that lower concentration of SA
might enhance the release of auxins and increase
the activity of GS, GOGAT, and GDH enzymes
(Hayat et al.
2012
).
6.2.1
Phytohormones Application
for Amelioration of Chromium
Phytotoxicity
1. Salicylic acid application
Several reports were published in the last decade
demonstrating the role of salicylic acid (SA)
applied as a seed soaking treatment on various
physiological processes. In several recent stud-
ies, application of SA through different modes
was found to be beneficial for the growth of
Ara-
bidopsis thaliana
under arsenic stress (Odjegba
2012
), wheat under salinity stress (Shakirova
2007
), tomato and amaranth under water stress
(Umebese et al.
2009
), garlic under drought
stress (Bideshki and Arvin
2010
), and common
bean under water stress (Sadeghipour and Aghaei
2012
). Hayat et al. (
2010
) reported that presoak-
ing of pea seeds in SA had a beneficial effect on
growth and photosynthesis with decreased oxida-
tive injuries caused by heavy metal stress. Simi-
larly, Fariduddin et al. (
2003
) investigated that
dry matter accumulation was significantly in-
creased in
Brassica juncea
with spray of SA. Fur-
thermore, Farooq et al. (
2010
) demonstrated ap-
plication of some other chemicals such as glycine
betaine (GB), nitric oxide, brassinosteroid (BR),
and spermine along with SA to improve growth
of rice under drought stress with a possible effect
on improved carbon assimilation, enhanced syn-
thesis of metabolites, and maintenance of tissue
water status. Addition of SA could induce activity
of H
+
-ATPase (Gordon et al.
2004
), which plays
an important role in the transport of multiple ions
through plasma membrane (Shi and Zhu
2008
).
Application of SA was also reported to increase
the Zn concentration, which is required for the
synthesis of indole-3-acetic acid (IAA) and has
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