Environmental Engineering Reference
In-Depth Information
6.2.6
Hydrogen Peroxide
in Amelioration of Cr(VI)
Phytotoxic Effects
carbohydrate metabolism and protein synthesis
(Taiz and Zeiger
2002
). Similarly, potassium (K)
also plays an important role in regulation in os-
motic potential in plant cells and also activates
many enzymes in respiration and photosynthe-
sis (Bassi et al.
1990
). In protein synthesis, K is
probably involved in several steps of the trans-
lation processes, including the binding of tRNA
to ribosomes (Evans and Wildes
1971
). The high
K concentrations in the sieve tubes are probably
related to the mechanism of phloem loading of
sucrose. The adverse effect of Cr was found to
be nullified by the supply of suitable amounts
of Fe and Zn in moong, gram, and pea plants,
possibly due to importance of these two essen-
tial nutrients in growth and metabolism of plants
(Vazquez et al.
1987
). In addition, Fe also plays
an important role as a component of enzymes in-
volved in the transfer of electron redox reaction,
like with cytochromes, and it is reversibly oxi-
dized from Fe
2+
to Fe
3+
during electron transfer.
Under condition of Fe deficiency, the activity of
both types of enzyme declines. Nath et al. (
2009
)
have shown that lower levels of tannery effluent
can be used for irrigation of
R. sativus
L. plants
in combination with Zn, K, and Fe sulfate. The
application of Zn in combination with tannery ef-
fluent has been shown to reduce the toxicity of
Cr, leading to increased growth.
The exogenous application of hydrogen peroxide
(H
2
O
2
) has been found to counter toxic effects of
several abiotic stresses (Yıldız et al.
2013
). There
are evidences from several studies that H
2
O
2
in-
creases tolerance of plants to salinity, drought,
heavy metal, and heat stress (Uchida et al.
2002
;
Xu et al.
2008
; Hu et al.
2009
). To evaluate the
ameliorating effects of H
2
O
2
(200 μM) on Cr(VI)
toxicity in canola (
Brassica napus
L.), Yıldız
et al. (
2013
) observed plant growth, chlorophyll
content, thiol contents, lipid peroxidation, anti-
oxidant enzymes, and the expression of metallo-
thionein protein (BnMP1) mRNA. Cr(VI) at
50 μM significantly decreased the plant growth
(fresh and dry weights) accompanied by in-
creased lipid peroxidation and decreased chlo-
rophyll content in leaves. H
2
O
2
pretreatment,
however, enhanced plant growth parameters and
led to the reduced levels of lipid peroxidation
and higher levels of pigment. In addition, H
2
O
2
pretreatment increased Cr accumulation in aerial
parts of seedlings. The tendency of increase in
thiol content under Cr(VI) stress was further in-
creased with H
2
O
2
pretreatment. The activities of
antioxidant enzymes such as SOD, APX, POD,
and CAT were differentially altered. SOD and
POD activities increased under Cr(VI) stress,
whereas APX and CAT activities decreased. This
study suggested that H
2
O
2
may act as a signal
that triggers defense mechanisms which in turn
protects canola seedlings from Cr(VI)-induced
oxidative damage.
6.3.2
Amendment in Phosphorus
Levels and Addition of Glucose
in Soil
Phosphorus (P) is well known as an essential and
limiting nutrient for plant growth and develop-
ment. P and Cr compete with each other during
the plant uptake process. Sayantan (
2013
) studied
the role of P in moderating the Cr toxicity in
R.
sativus
L. The toxic effects of Cr and the modera-
tion of toxicity due to P amendment were deter-
mined as accumulation of Cr, nitrogen, and P in
root tissues, and their effects were also examined
in the changes in biomass, chlorophyll, and anti-
oxidant enzyme levels. Cr and N accumulation
were almost doubled at the highest concentration
of Cr supply, without any P amendment, whereas
6.3
Soil Amendments for Enhanced
Cr Tolerance in Plants
6.3.1
Potential of Micro- and
Macronutrient Amendments
in Soil
Many plant enzymes require Zn ions for their
activity and for chlorophyll biosynthesis, while
Zn deficiency is associated with an important
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