Basic HTML Version
Plant Gene and Trait, 2013, Vol.4, No.20, 109
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123
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Figure 6 Effects of H
2
O
2
pre-treatment on the activities of Gly I
(A) and Gly II (B) in mustard seedlings under drought stress
conditions. Other details as in figure 3
Compared to drought treatment, treatment with
H
2
O
2
+drought showed a significant (P<0.01) increase
(22%) in Gly II activity.
1.5 Effect of
H
2
O
2
pre-treatment on
H
2
O
2
and MDA
levels
The level of endogenous H
2
O
2
showed a significant
(P<0.01) increase (2
-
fold) in response to drought
stress as compared to control group (Figure 7A).
Treatment with H
2
O
2
+drought also showed a
significant (P<0.01) increase (18%) in H
2
O
2
as
compared to the control group. Importantly, H
2
O
2
pre-treatment bought a substantial decline (36%) in
H
2
O
2
content as compared to the seedlings subjected
to drought stress without pre-treatment.
Figure 7 Effects of H
2
O
2
pre-treatment on endogenous H
2
O
2
(A)
and MDA (B) levels in mustard seedlings under drought stress
conditions. Other details as in figure 3
The level of lipid peroxidation, measured as MDA,
showed a significant (P<0.01) increase (103%) as
compared to the control group (Figure 7B). Treatment
with H
2
O
2
+drought also showed a significant (P<0.01)
increase (38%) in MDA content as compared with
control group. Most importantly, H
2
O
2
pre-treated
seedlings showed a significantly (P<0.01) lower (32%)
level of MDA content as compared to the seedlings
subjected to drought stress without H
2
O
2
pre-treatment.
2 Discussion
Acceleration in ROS production under abiotic stress
conditions is one of the most important and best
documented features of plants stress response.
Hydrogen peroxide in plant functions as a
double-edged sword: its lower concentration has been
demonstrated to be a signal transducer whilst
overproduction of H
2
O
2
could lead to oxidative
damage (Miller et al., 2008; Mittler et al., 2011;
Suzuki et al., 2012). To overcome the oxidative stress,
it is important to maintain a stronger ROS-scavenging
ability under stress conditions, especially in plant
leaves where photosynthesis is dramatically impacted.
Plants under abiotic stress have evolved a defense
system to counteract the ROS induced damage by
increasing the activity of ROS scavenging enzymes.
An increased capacity of the antioxidant defense
system and glyoxalase system is one of the possible
mechanisms responsible for oxidative stress tolerance
as demonstrated by the existence of stress-resistant
lines with naturally enhanced antioxidant systems
(El-Shrabarwi et al., 2010) or the properties of
transgenic plants over-expressing particular antio-
xidant enzymes (Xu et al., 2008; Wang et al., 2010b;
Wang et al., 2012). Direct evidence has recently been
provided for the role of H
2
O
2
in inducing
stress-related promoters and genes (Mittler et al.,
2012). Drought or desiccation tolerant cells undergo
less oxidative damages than cells that are sensitive to
these stresses (Turkan et al., 2005). This could be the
result of an effective decrease in ROS production or of
the activation of effective antioxidant systems, or both.
The present study hypothesized that transient
pre-exposure of seedlings to H
2
O
2
may induce
tolerance to subsequent drought stress in mustard
seedlings through the activation of antioxidative
and glyoxalase defense system.
Drought stress invariably leads to oxidative stress in
plant cells through direct enhancement of ROS
production or indirectly through excessive accumulation
of MG that has the capacity to inhibit antioxidant
enzyme activity. To control the over-accumulation of
ROS and MG plant cell express a network of
antioxidative and glyoxalase system to counter the
adverse effects imposed by them. Ascorbate and
GSH are the two most important water soluble
non-enzymatic antioxidant related to a broad range of
biological functions including growth and development,