2nd IeCAB symposium June 1-15 2009.
Mohamed M. Ibrahim1* and Sameera O. Bafeel2
1Science
Department ( Biology section), Teacher's College, King Saud University, Riyadh, Saudi Arabia
2Biology
Department, College of Science, King Abdul Aziz University, Jeddah, Saudi Arabia
E. mail. [email protected] , [email protected]
2
What
is
an
Oxidant
and
Oxidative
Stress?
Oxidant : Refers to all “Reactive oxygen/Nitrogen
species”
including
O2•,
H2O2
and
•OH
and
•NO.
Oxidative stress : Is an imbalance between prooxidants and antioxidants in favor of the pro-oxidant
leading to cell injury or death.
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Environmental stresses such as heavy metals that
disturb the normal cellular metabolism can upset
the balance of production and quenching of
reactive oxygen species (ROS) like O2•, H2O2 and
•OH and •NO.
.
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2nd IeCAB symposium June 1-15 2009.
Inevitable biological process associated with general
decline in physiological function.
Increased probability of death with accumulation of
diverse, adverse changes as an organism gets older.
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2nd IeCAB symposium June 1-15 2009.
- A rapid change of gene expression in plants in
response to
heavy metal stress is important for
environmental adaptation.
- mRNA Differential Display technique was used in this
study to analyze alterations in gene expression in garden
cress (Lepidium sativum) in response to different
concentrations
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of
lead.
2nd IeCAB symposium June 1-15 2009.
- Some Molecular, physiological as well as the response
of oxidative stress indices to Pb2+ toxicity were
investigated in an effort to identify the possible
involvement of Pb2+ in the generation of oxidative
stress.
Also we investigated the molecular and
physiological mechanisms by which Lepidium
sativum cope with Pb2+ toxicity to overcome the
drastic effect of ROS.
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Estimation of lipid peroxides
Determination of lead content
Determination of superoxide anion
radical (O2_– ) production rate
Isoenzyme profile of some antioxidant enzymes
Semi-quantitative RT-PCR
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2nd IeCAB symposium June 1-15 2009.
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2nd IeCAB symposium June 1-15 2009.
Table 1: Effect of increasing concentration of Pb2+ in the growth medium on Lead
accumulation in shoot and root and total lipid peroxide of Lepidium sativum
roots after 10 days treatment. Each value is the mean of three replicates ( SD).
Values carrying asterisk are significantly different at P  0.05.
Pb2+
(µg g-1 D.W)
Treatments
Pb2+
(ppm)
Shoot
Root
C
0.00
0.00
80.24± 4.23
100
0.080.010
0.280.019
91.56± 4.83
200
0.240.03‫٭‬
0.900.17‫٭‬
107.87±5.23‫٭‬
400
0.380.08‫٭‬
1.940. 13‫٭‬
128.76 ± 6.23‫٭‬
600
0.850.10‫٭‬
3.180.91‫٭‬
176.43± 7.23‫٭‬
10
Total lipid peroxide TBARS
(nmol g-1 F.W.)
2nd IeCAB symposium June 1-15 2009.
Fig. (1): Changes in the rate of superoxide production rate in
roots of control and stressed plants of Lepidium sativum
subjected to various concentrations of Pb2+ for 10 days. The
control for these measurements are non treated roots. Each
value represents the mean ±SE of five replicates.
Fig. 2. Effect of increasing concentration of Pb2+ in the growth medium on
SOD, CAT and APX activities in roots of Lepidium sativum after 10 days
treatment. Values are mean±/S.D. Based on three replicates, bars
carrying
asterisk
are
significantly
different
at
P

0.05.
2nd IeCAB symposium June 1-15 2009.
Fig.3: Isoenzyme profile of superoxide dismutase (SOD), A;
catalase(CAT), B; ascorbic peroxidase (APX), C in enzyme
preparations from leaves of 25 days grown seedlings of Lepidum
sativum. Seedlings were raised for 10 days under different
concentrations of Pb2+ in the growth medium. (C) Control; 100 =
100 ppm Pb2+; 200 = 200 ppm Pb2+; 400 = 400 ppm Pb2+; 600 =
600 ppm Pb2+. For details see text.
2nd IeCAB symposium June 1-15 2009.
2nd IeCAB symposium June 1-15 2009.
Deleterious effects resulted from the oxidative stress
caused by lower and moderate concentrations of lead
can be prevented by the defense mechanism in plants
via scavenging of the ROS.
2nd IeCAB symposium June 1-15 2009.
The antioxidative system, is composed not only of
the low-molecular components but also of enzymatic
components such as SOD, CAT, and APX.
Can serve in convalescing from deleterious effect of
ROS.
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2nd IeCAB symposium June 1-15 2009.
When Pb2+ concentration exceeded 200 ppm, the
emergence rate of roots of Lepidium sativum was
inhibited, this effect became more marked when
Pb2+concentration was above 400 ppm.
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2nd IeCAB symposium June 1-15 2009.
Both the plant’s physiological oxidative
indicator
(lipid
peroxide)
and
the
stress
indicator
of
unbalanced metabolism of free radicals (superoxide
anion radical (O2_–) production rate) varied with Pb2+
accumulation especially in roots.
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2nd IeCAB symposium June 1-15 2009.
A close relationship was found between the
activities of enzymes (SOD, CAT and APX) and
Pb2+accumulation
in
roots.
Also the differential gene expression of different
isozymes was associated with varying Pb2+
treatment.
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Genetic,
Physiological
and
Biochemical
responses of some plants to interactive biotic and
abiotic
stress.
Effect of heavy metals on ultra structure and
antioxidant
isozymes
of
some
important plants.
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2nd IeCAB symposium June 1-15 2009.
economically
Deanship of Scientific Research at King Abdul-Aziz University,
for supporting this research project no. 428/524;
Professor Nigel, Professor of Environmental Pollution for his
suggestions;
Mubarak City for Scientific Research for excellent technical
assistance in RT-PCR.
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2nd IeCAB symposium June 1-15 2009.
2nd IeCAB symposium June 1-15 2009.
Thank You
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2nd IeCAB symposium June 1-15 2009.