Basic HTML Version
Plant Gene and Trait, 2013, Vol.4, No.20, 109
-
123
http://pgt.sophiapublisher.com
112
possible mechanisms of H
2
O
2
induced abiotic stress
tolerance in plants, however, still today there is no
evidence whether H
2
O
2
priming could induce a
systemic upregulation of glyoxalase system that
ultimately led to drought induced oxidative stress
tolerance. The prime objective of this study is
therefore to investigate the effects of H
2
O
2
pre-treatment on drought tolerance in mustard
seedlings with special reference to ROS and MG
metabolism. Towards this objective, a biochemical
approach was employed, aiming to assess several key
components of ROS in MG detoxification pathways
and to explore the possible biochemical mechanisms
of oxidative stress tolerance in mustard seedlings
exposed drought stress. Our data indicate that drought
tolerance is invoked by H
2
O
2
through the modulation
of antioxidative and glyoxalase systems.
1 Results
1.1 Effects of
H
2
O
2
pre-treatment on AsA and GSH
contents
Upon exposure to drought stress, leaf AsA content
showed a significant (P<0.01) increase (34%) whereas
a non-significant increase (6%) was observed in H
2
O
2
pre-treated seedlings compared to the control group
(Figure 3A). Compared with drought stress treatment,
Figure 3 Effects of H
2
O
2
pre-treatment on
ascorbate (AsA) (A),
reduced glutathione (GSH) (B), oxidized glutathione (GSSG)
(C) and GSH/GSSG ratio (D) in mustard seedlings under
drought stress conditions. Mean (±SD) was calculated from
three replicates from each treatment. Dr and H+Dr indicate
drought, hydrogen peroxide+drought stresses, respectively.
Bars with different letters are significantly different at p<0.01
applying LSD test
treatment with H
2
O
2
+drought showed a significant
(P<0.01) decrease (20%) in AsA content.
When comparing drought treated plants to the control,
the level of GSH showed a 2-fold increase in leaf
tissues (Figure 3B). Drought exposure with H
2
O
2
pre-treated also showed a significant (P<0.01)
increase (19%) in GSH content as compared to control.
Compared with drought stress treatment, treatment
with H
2
O
2
+drought showed a significant (P<0.01)
decrease (39%) in GSH content.
Compared to the control group, drought stress caused
a sharp (P<0.01) increase (338%) in GSSG content
(Figure 3C). Compared with drought stress treatment,
treatment with H
2
O
2
+drought showed a significant
(P<0.01) decrease (77%) in GSSG content.
Drought stress treatment led to a significant (P<0.01)
decrease (56%) in redox ratio (GSH/GSSG) relative to
control. Treatment with H
2
O
2
+drought showed a
non-significant increase (16%) in redox ratio
compared to the control. Compared with drought
stress treatment, treatment with H
2
O
2
+drought showed
a significant (P<0.01) increase (98%) in redox ratio.
1.2 Effect of
H
2
O
2
pretreatment on ascorbate-
glutathione (AsA-GSH) cycle enzyme activities
Influences of H
2
O
2
on the activities of AsA-GSH cycle
enzymes are shown in Fig. 4. As compared to the
control group, drought stress resulted in a significant
(P<0.01) decrease in APX activity (Figure 4A).
Furthermore, treatment with H
2
O
2
+drought caused a
significant (P<0.01) increase (26%) in APX activity
relative to control. Compared with drought stress
treatment, treatment with H
2
O
2
+drought showed a
significant (P<0.01) increase (53%) in APX activity.
Seedlings treated with drought stress showed a slight
increase (17%) in MDHAR activity when compared
with control group (Figure 4B). H
2
O
2
pre-treatment
didn’t significantly change the MDHAR activity
relative to control. The activity of MDHAR remains
unchanged in H
2
O
2
pre-treated and non-treated
drought-stressed seedlings.
The activity of DHAR showed a significant (P<0.01)
increase (26%) in response to drought stress (Figure
4C)
.
Treatment with H
2
O
2
+drought caused a
significant (P<0.01) increase (22%) in DHAR activity
as compared to the control group. Importantly, H
2
O
2