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Plant Gene and Trait, 2013, Vol.4, No.20, 109
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Figure 2 Reactive oxygen species detoxification systems in plants. Abbreviations are defined in the text
Similarly, plants avoid excessive accumulation of MG
under stress through the up-regulation of glyoxalase
system that convert MG to less toxic hydroxylacids
and glyoxalase system play crucial role in plant
abiotic stress tolerance by regulating MG levels
appropriate level to perform its signalling functions
and by regulating GSH-based ROS detoxification. A
number of recent studies in plants involving stress
tolerant and transgenic plants have demonstrated that
both ROS and glyoxalase removal systems are equally
important for stress tolerance in plants (Hoque et al.,
2008; Kumar and Yadav, 2009; El-Shabrawi et al.,
2010; Hossain and Fujita, 2009; 2010; Hossain et al.,
2009; 2010; 2011b; 2012a; 2012b; 2013a; 2013b;
Upadhyaya et al., 2011; Mostofa and Fujita, 2013) and
favourable modulation of both of these detoxification
pathways rendering the plants more tolerant to various
abiotic stresses.
Hydrogen peroxide has received the most attention
from the scientific community being a master
regulator of plant stress signalling pathways. Many
evidences have recently emerged that H
2
O
2
also
functions as an important signal molecule mediating
the phenomena of acclimation and cross-tolerance, in
which previous exposure to one stress can induce
tolerance of subsequent exposure to the same or
different stresses (Gong et al., 2001; Neill et al., 2002;
Petrov and Van Breusegem, 2012; Hossain et al.,
2013a; 2013b). A transient increase in the endogenous
levels of H
2
O
2
obtained by exogenous cold or heat
pre-treatment can lead to drought stress tolerance in
different plant species (Gong et al., 2001; Hossain et
al., 2013a). Hydrogen peroxide at optimum level acts
as a signal that induces the expression of numerous
defense genes and activates multiple defense
responses to abiotic stresses, while excessive
accumulation leads to cellular oxidative damage and
even programmed death (Levine et al., 1994; Prasad et
al., 1994). Hydrogen peroxide positively used by
plants to acclimate some stress-responsive genes that
help them to cope with environmental changes. Plenty
of research demonstrated that the appropriate level of
H
2
O
2
pre-treatment can enhance abiotic stress
tolerance by modulating multiple stress responsive
pathways including antioxidant defense systems. Li et
al. (2011) reported that exogenously applied H
2
O
2
decreased the MDA content, enhanced the GSH
content and increased the activities of SOD, POD,
CAT and APX in salt-stressed wheat seedlings. Jing et
al (2009) found that pre-treatment with H
2
O
2
can
enhanced drought-induced oxidative stress tolerance
by modulating SOD, CAT, GPOX, APX, DHAR,
DHAR, and GR activities and the levels of AsA and
GSH. Later on, Liu et al (2010) showed that H
2
O
2
pre-treatment induces drought stress tolerance by
up-regulating the activities of SOD, APX, MDHAR,
DHAR, GR, CAT as well as AsA and GSH content
and their redox state with a concomitant decrease in
oxidative damage as indicated by lower O
2
•−
, H
2
O
2
and MDA levels. Hu et al (2009) showed that
exogenous H
2
O
2
application induced Cd-stress
tolerance by inducing the antioxidant enzymes (SOD,
CAT, GPX, APX and GST) as well as by elevating the
GSH and AsA pool. Recently, Wang et al (2010a)
showed that pre-treatment with H
2
O
2
turfgrass cultivar
showed enhanced chilling tolerance by increasing the
activities of CAT, POD, APX, GR, and GPX.
Although a large number of studies have shown the