2nd IeCAB symposium June 1-15 2009.

2nd IeCAB symposium June 1-15 2009.2

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 .mibrahim@ksu.edu.sa , sbafil@kau.edu.sa

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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 pro-

oxidants and antioxidants in favor of the pro-

oxidant leading to cell injury or death.

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Environmental stresses such as heavyEnvironmental stresses such as heavy metalsmetals that that

disturb the normal cellular metabolism disturb the normal cellular metabolism can upsetcan upset

the the balance of production and quenching of balance of production and quenching of

reactivereactive oxygen species (ROS)oxygen species (ROS) like O like O2•, H•, H2OO2 and and

•OH and •NO•OH and •NO .

.

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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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- 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 of lead.

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- 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 superoxide anion radical (O2_– ) production rate

Determination of lead content

Isoenzyme profile of some antioxidant enzymes

Semi-quantitative RT-PCR

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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.

10

Treatments Pb2+

(ppm)

Pb2+

(µg g-1 D.W)Total lipid peroxide TBARS

(nmol g-1 F.W.)

ShootRoot

C0.000.0080.24± 4.23

1000.080.0100.280.01991.56± 4.83

2000.240.030.90٭0.17٭5.23±107.87٭

4000.380.081.94٭0. 13٭6.23 ± 128.76٭

6000.850.103.18٭0.91٭

٭7.23 176.43±

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.

2nd IeCAB symposium June 1-15 2009.

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.

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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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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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Both the plant’s physiological oxidative stress

indicator (lipid peroxide) and the indicator of

unbalanced metabolism of free radicals (superoxide

anion radical (O2_–) production rate) varied with Pb2+

accumulation especially in roots.

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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.

2nd IeCAB symposium June 1-15 2009.

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 economically

important plants.

21

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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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Thank You