1Department of Botany, Faculty of Science, Ain Shams University, Cairo, Egypt2Department of Biology, Faculty of Science, Taif University, Taif, Saudi Arabia

*Corresponding author: mf_mansour@yahoo.com

Effect of heavy metals on plasma membrane lipidsand antioxidant enzymes of Zygophyllum species

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EurAsian Journal of BioSciences Eurasia J Biosci 6, 1-10 (2012)DOI:10.5053/ejobios.2012.6.0.1

Heavy metals are defined as group of elements

that have specific weights higher than about 5

g/cm3. Iron, Mn, Mo, Ni, Zn and Cu are essential

micronutrients that required for normal growth and

metabolic processes in plants (Vangronsveld and

Clijsters 1994). Cd, Pb, Cr and Hg are nonessential

and highly toxic for plants (Devi and Prasad 1998,

Sebastiani et al. 2004, Rai et al. 2004). Heavy metals

inhibit physiological processes such as respiration,

photosynthesis, cell elongation and affect plant

water relationship as well as mineral nutrition

(Vangronsveld and Clijsters 1994, Zornoza et al.

2002). Large areas of land are contaminated with

heavy metals resulting from urban activities,

agricultural practices and industry (Khan et al. 2000,

Ciemense 2001).

Damage of the cellular membranes, especially for

the plasma membrane, is one of the primary events

in heavy metal toxic effects in plants (Harwood

1995, Janicka et al. 2008). Heavy metals disrupt

cellular membranes resulting in the conversion of

unsaturated fatty acids into small hydrocarbon

fragments such as malondialdehyde (Tappel 1973,

Kappus 1985). Metal ions can also replace calcium

ions at its essential sites on the membranes (Breckle

Received: September 2011Accepted: January 2012

Printed: January 2012

INTRODUCTION

AbstractBackground: Heavy metals are major environmental pollutant when they present in highconcentration in soil and have toxic effects on growth and development of plants. Industrialactivities result in heavy metal pollution of large areas of land, which greatly affects naturalvegetation. Understanding the mechanism of how plants combat heavy metals adverse effects ishence of great importance.Materials and Methods: Two different localities were chosen; one locality was in the vicinity ofgypsum factory and the other one was 25 km away from the factory. Two Zygophyllum species (Z.album and Z. coccineum) were naturally grown in the studied areas. The effects of soil heavy metalstress on shoot heavy metal concentrations, lipid peroxidation, antioxidant enzyme activities andthe root plasma membrane (PM) lipid composition were analyzed.Results: Heavy metal concentrations and Lipid peroxidation increased in the shoot of both speciesgrown in the polluted area. The activities of ascorbate oxidase (ASO), guaiacal peroxidase (GPX),ascorbate peroxidase (APX) and superoxide dismutase (SOD) were increased whereas these ofcatalase (CAT) were decreased in both species under the polluted conditions. PM total lipids,phospholipids, glycolipids and sterols were decreased in Z. album and Z. coccineum as a result of thepolluted soil. Heavy metal stress increased phosphatidylethanolamine (PE) and decreasedphosphatidylinositol (PI) and phophatidylglycerol (PG), with no significant change inphosphatidylcholine (PC) in the root PM of both species. Phosphatidylserine (PS) decreased in thePM of Z. album whereas it increased in the PM of Z. coccineum under the pollution conditions. Heavymetal stress changed the composition and concentration of fatty acids of the root PM, resulting inincreased sat/unsat ratio of both species.Conclusion: the results suggest that efficient antioxidant machinery and favorable PM lipidhomeostasis are important to enable Zygophyllum species to withstand the prevailing heavy metalstress.Keywords: Antioxidant enzyme, fatty acid, heavy metal, lipid peroxidation, plasma membrane lipid,Zygophyllum sp.

Morsy AA, Salama HHA, Kamel HA, Mansour MMF (2012) Effect of heavy metals on plasmamembrane lipids and antioxidant enzymes of Zygophyllum species. Eurasia J Biosci 6: 1-10.

DOI:10.5053/ejobios.2012.6.0.1

Amal Ahmed Morsy1, Karima Hamid Ali Salama2, Hend Ahmed Kamel1, Mohamed Magdy Fahim Mansour2*

©EurAsian Journal of BioSciences

and Kahle 1991). Furthermore, plant plasma

membrane is dynamic and its lipid composition/

structure is changed with variations in the external

environment. Plasma membrane changes might

have an adaptive value or injuriously affects

membrane properties and functions (Mansour et al.

2003, Mansour and Salama 2004).

Reactive oxygen species (ROS) are regarded as

the main source of damage to cells under the biotic

and abiotic stresses (Mittler 2002, Candan and

Tarhan 2003, Gara et al. 2003, Vaidyanathan et al.

2003). This is because under normal conditions

production and destruction of ROS is well regulated

in cell metabolism (Mittler 2002). When a plant is in

the harsh conditions, ROS production will overcome

scavenging systems and oxidative stress will burst.

ROS includes superoxide (O2.-), hydrogen peroxide

(H2O2) and hydroxyl radical (HO·) (Mittler 2002). ROS

are highly cytotoxic and can seriously react with vital

bio-molecules such as lipids, proteins, nucleic acid,

these can cause lipid peroxidation, protein

denaturation and DNA mutation (Mittler 2002,

Quiles and López 2004). Plants have developed

various protective mechanisms to eliminate or

reduce ROS deleterious effects (Mittler 2002, Beak

and Skinner 2003). Antioxidant system consists of

enzymatic and non-enzymatic compounds.

Enzymatic antioxidants include superoxide

dismutase, catalase, peroxidases, glutathione

reductase and ascorbate reductase (Mittler 2002,

Candan and Tarhan 2003). Non-enzymatic

antioxidants are ascorbate, glutathione, tocopherol

and carotenoids.

The current study was undertaken to analyze the

changes in the heavy metal composition, plasma

membrane lipids, lipid peroxidation and antioxidant

enzymes of two Zygopyllum species (Zygophyllum

album and Zygophyllum coccinum) grown in their

natural habitats in absence and presence of heavy

metal pollution. These changes will be correlated

with the responses of the two Zygopyllum species

grown in polluted and non-polluted habitats.

The study areas and plant materials

The present work was conducted in two different

desert habitats at south Sinai, Egypt; the first habitat

was Ras Malaab where the factory of gypsum exists.

The second habitat was Wadi Thal placed 25 km

away from the factory. The plant species used in the

present investigation were Zygophyllum album L.

and Zygophyllum coccineum L.

Soil samples

The samples of two composite soil were collected

at three depths (0-20 cm, 20-40 cm and 40-60 cm).

One sample was collected near an industrial effluent

channel and the other sample was collected 25 km

away. The soil samples collection were replicated

three times over space. Granulometric analyses of

the soil samples were accomplished using the sieve

method according to Jackson (1967). Soil-water

extract (1:10) was used for the different

determinations as described by Richards (1954). Al,

Cu, Zn, and Fe were determined using atomic

absorptions spectrophotometer (Unicam 929 AA,

UK) as described by Black (1965).

Plant samples

The samples of shoot and root of both species

were collected from their natural vegetation in Ras

Malaab and Wadi Thal. The samples were replicated

three times over space. The samples were kept in

liquid nitrogen immediately after collection, and

then stored under -80°C for the further analysis.

Determination of antioxidant enzyme

activities

The shoots were homogenized in a chilled mortar

for 30s using 50 mM potassium phosphate buffer

(pH 7). Homogenates were centrifuged at 15,000 g

at 4°C and the supernatant was used for enzyme

activities. The activity of APX was measured

according to Zhang et al. (2007). The reaction

mixture contained 50 mM potassium-phosphate

buffer, 0.5 mM L-ascorbate, 0.1 mM H2O2 and the

enzyme extract. H2O2 dependent oxidation of

ascorbate was followed by a decrease in absorbance

at 290 nm. APX activity was expressed as the

absorbance decrease (ΔE) min-1 g-1 F. W. GPX activity

was estimated according to Hammerschmidt et al.

Morsy et al.

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EurAsian Journal of BioSciences 6: 1-10 (2012)

MATERIALS AND METHODS

(1982). The reaction mixture contained 25 mM

potassium phosphate buffer (pH 7.0), 0.2 mM

guaiacol, 0.09 mM H2O2 and the enzyme extract.

H2O2-dependent oxidation of guaiacol was followed

by an increase of absorbance at 470 nm. Enzyme

activity was calculated as the increase of absorbance

(ΔE) min-1 g-1 F. W. For ASO, the method of Chinoy et

al. (1976) was used. The reaction mixture consisted

of 1 mL of 0.1 mM ascorbic acid, 1 mL of 0.5 mM

phosphate buffer (pH 6.8) and 2 mL of enzyme

extract. This reaction mixture was incubated at 37°C

for 25 min. After incubation, the 2, 6-dichlorophenol

indophenol was added and the absorbance was

measured at 620 nm. CAT activity was assayed

spectrophotometrically (Hitachi U-3000, Japan) by

measuring the decrease in absorbance at 240 nm

because of H2O2 decomposition (Zhang et al. 2007).

SOD activity was determined by measuring the

inhibition of the auto-oxidation of pyrogallol using a

method described by Zhang et al. (2007). Ten mL of

the reaction mixture comprised: 3.6 mL of distilled

water, 0.1 mL of the enzyme extract, 5.5 mL of 50

mM phosphate buffer (pH 7.8) and 0.8 mL of 3 mM

pyrogallol (dissolved in 10 mM HCl). The rate of

pyrogallol reduction was measured at 325 nm using

UV- spectrophotometer. One unit of enzyme activity

was defined as the amount of the enzyme that

resulted in 50% inhibition of the auto-oxidation rate

of pyrogallol at 25°C (Zhang et al. 2007). The enzyme

activity was expressed as unit/mg protein.

Determination of malondialdehyde (MDA)

MDA content, as an indicator of lipid

peroxidation, was determined using the procedure

described by Zhang et al. (2007). The plant shoot was

homogenized in 1% trichloroacetic acid and then

centrifuged at 10,000 rpm for 15 min. Supernatant

was heated with 0.05 thiobarbituric acid for 30 min

at 95°C. The heated supernatant was then

centrifuged at 5000 rpm for 5 min and the

absorbance was measured at 532 and 600 nm.

Plasma membrane isolation

Two-phase partitioning method (Mansour et al.

2002, Salama et al. 2007) was used to isolate the

root PM of Zygophyllum album and Zygophyllum

coccinum. The root was washed in cold bidistilled

water and homogenized in a blender with a

homogenization medium (the pH was adjusted to 7.5

with Hepps-KOH): 250 mM sucrose, 5 mM EGTA, 5

mM EDTA, 10 mM KF, 25 mM MOPS, and 1 mM PMSF.

Two mM of DTT was added as powder. The

homogenization of the root tissue was carried out

three times for 20-s each with a 10-s pause. The

homogenate was filtered through miracloth. A new

homogenization medium was added to the tissue

and was homogenized once again. The pooled

solution was centrifuged at 10,000 g for 20 min. The

supernatant containing the PM and other

membranes was then centrifuge at 50,000 g for 1 h.

The microsomal membrane pellet was resuspended

in 5 mM potassium phosphate buffer (pH 7.8)

containing 250 mM sucrose and 4 mM KCl. The PM

were prepared by partitioning of microsomal

suspension in 27 g aqueous polymer two-phase

system containing 6.5% dextrane T-500 (Pharmacia),

6.5% polyethylene glycol 3350 (Sigma) in 250 mM

sucrose, 5 mM potassium phosphate buffer (pH 7.8),

4 mM KCl and 25 mM DTT. Into the two-phase

system 108 μL of the solution (333 mM DTE and 33.3

mM EDTA) was added, mixed thoroughly and

centrifuged at 1,500 g for 5 min. The microsomal

pellet was subjected to three successive phase

partitioning steps. The upper phase, containing the

PM fraction, centrifuged at 50,000 g for 1 h and the

pellet resuspended in 1 mL of storage buffer (pH

7.5). All steps of the PM isolation were carried out at

0-4°C. The purity of our PM preparation was based

on Mansour et al. (1994).

PM lipid extraction and separation

Boiled isopropanol was immediately added to the

PM suspension to inhibit the activity of lipase (Kates

1972). Lipids were then extracted with 3.75 mM

chloroform: isopropanol (2:1, v/v) and 2.25 mL of 0.1

M KCl was added to enhance the chloroform phase

separation. Then, the mixture was centrifuged in

cold room at 1,000 g for 5 min. The upper water

phase was re-extracted with 2 mL chloroform. The

first and second chloroform phases (containing

lipids) were collected and dried under CO2 stream.

The dried lipids were dissolved in 2.5 mL chloroform

and stored at -80°C until analysis.

Determination of PM fatty acids

The method of Mansour et al. (2002) was used for

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Morsy et al.EurAsian Journal of BioSciences 6: 1-10 (2012)

the analysis of PM fatty acids. One mL of lipid

extract, 6 mL of benzene and 1.5 mL of 10% alcoholic

KOH were mixed together. The tubes were refluxed

for 4 h in a boiling water bath and then the mixture

was evaporated. Excess of diethyl ether was added

and shaken well. The organic phase (upper phase)

was pipetted and the aqueous phase (lower phase)

was further washed three times with diethyl ether.

The aqueous phase containing fatty acids was

acidified by 1 N H2SO4 and the pH was adjusted to

two. The sample was methylated by the addition of

2.5 mL of H2SO4 and 50 mL methanol and refluxed

for 24 h. The mixture was evaporated; excess of

diethyl ether was added and shaken well. The

organic phase was evaporated to determine the

different fatty acids. The fatty acid methyl esters

were determined by gas chromatography (HP-5890,

Little Falls, DE) equipped with a flame-ionization

detector. An HP-FFAP (free fatty acid phase) column

(25 m, 0.3 mm diameter) was used with helium (35

cm s-1) as a carrier gas. The injector temperature was

250°C, detector temperature was 260°C, and the

temperature program during the analysis went from

50 to 240°C (7°C min-1), after which temperature was

kept constant at 240°C for 30 min.

Determination of PM phospholipids

Phospholipids (polar lipids) were assayed

according to Deinstrop and Weinheim (2000). The

lipid extract was spotted along a glass thin layer

chromatography plate (TLC, Merk, Germany).

Phospholipid classes were separated by two-

dimensional TLC with solvent mixtures of

chloroform: methanol: deionized bidistilled water

(75: 25: 2.5, v/v) in the first direction. After allowing

sufficient time for drying, the plate was developed

at right angles to the first development in

chloroform: methanol: acetic acid: water (80: 9: 12: 2,

v/v) for the second direction. After separation of

phospholipids, spots were located by exposure to I2

vapor. Individual phospholipids were identified by

co-chromatography with authentic standards. The

area on TLC corresponding to each individual

phospholipids was marked and scraped into a test

tube and 0.5 mL HCl was added to neutralize silicate.

All tubes were heated for 10 min in a sand bath.

After cooling, 0.26 mL of 70% perchloric acid was

added. The tubes were closed with a glass covers

and heated at 180°C for 20 min and cooled. Next, 3.3

mL of deionized bi-distilled water, 0.4 mL of 10%

ascorbic acid were added. After each addition, the

contents of the tube were mixed thoroughly. The

tubes were then heated for 5 min in a boiling water

bath to develop the color and allowed to stand until

the color was settled for 5 min. The absorbance of

the developed color was read at 797 nm. The

standard curve of KH2PO4 was always run together

with samples.

Soil and plant analysis

Industrial activities in Ras Malaab area resulted in

significant increase of soil heavy metal

concentrations comparing with Wadi Thal soil (Table

1). This result is consistent with those of Khan et al.

(2000) and Ciemense (2001) who reported that large

areas of land are contaminated with heavy metals as

a result of urban activities and industry. The heavy

metal content of the soil samples of Ras Malaab

exceeded that established by Anonymous (1986) for

Al3+ and was very close to exceed the permissible

limits for Zn2+. Table 1 showed increased heavy

metal pollution of Ras Malaab soil, which was

reflected in increasing their level in the shoot of

both species (Table 2). Heavy metal contents of the

shoot of both species were significantly increased in

Ras Malaab area comparing with those of Wadi Thal,

and more so in Z. coccineum (Table 2). On the

percentage basis, the greatest increase was found in

Al3+, Zn2+ and Cu2+ in the shoot of both species

(Table 2). Previous published data indicated that soil

heavy metal pollution increased heavy metal

concentrations in different plant species (Sanders et

al. 1986, Devi and Prasad 1998, Sebastiani et al.

2004, Rai et al. 2004, Tohidi et al. 2009). It is thus

obvious that industrial activities polluted the soil of

Ras Malaab, which resulted in increased heavy metal

levels in the shoots of both Zygophyllum species

Lipid peroxidation

MDA concentration increased in the shoot of

both species grown in the polluted soil of Ras

Malaab (Table 3), the increase was greater in Z.

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Morsy et al.EurAsian Journal of BioSciences 6: 1-10 (2012)

RESULTS AND DISCUSSION

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Morsy et al.EurAsian Journal of BioSciences 6: 1-10 (2012)

album than Z. coccineum. Lipid peroxidation

observed in the current work is indicative of heavy

metal-induced oxidative stress in both species. Our

results are in agreement with previous reports

where lipid peroxidation increased under soil heavy

metal pollution in different plant species (Chaffai et

al. 2005, Chaffai et al. 2009, Janicka et al. 2008). The

results of lipid peroxidation were comparable with

those of reactive oxygen species scavengers

(antioxidant enzyme activities) reported in the

following section (Table 3), where the increase in the

antioxidant enzyme activities was greater in Z. album

than Z. coccineum, in order to alleviate the greater

oxidative stress in induced Z. album.

Antioxidant enzymes

Antioxidant enzymes are very good biochemical

markers of stress and increasing their activities

could be a potential for remediation (Rucinska et al.

1999, Mittler 2002, Zembala et al. 2010). Except CAT,

the activities of GPX, ASO, APX and SOD were

increased in both species (Table 3), more so with

SOD. On the percentage basis, the increase in the

antioxidant enzyme activities was greater in Z. album

than in Z. coccineum (Table 3) to scavenge greater

lipid peroxidation observed in Z. album. Similar

results have been reported in different plant

species, where oxidative stress-induced by heavy

metals was alleviated by increasing antioxidant

enzyme activities (Rucinska et al. 1999, Ciemense

2001, Candan and Tarhan 2003, Zembala et al. 2010).

Increased oxidative defense systems have been

reported to be correlated with tolerance to

different stress conditions, thus plants perform

normally under the adverse environment (Mittler

2002, Candan and Tarhan 2003, Zembala et al. 2010).

Decreased activity of CAT observed in the current

study was previously found in pea seedlings under

cadmium stress (Sandalio et al. 2001). It can be

concluded that soil heavy metal pollution enhanced

oxidative stress in both Zygophyllum species, and

both species combat the heavy metal stress via

production of scavenging systems.

Table 1. Minerals and heavy metal concentrations of Ras Malaab (polluted) and Wadi Thal (unpolluted) soils.

Table 2. Shoot minerals and heavy metal concentrations of two Zygophyllum species grown in Ras Malaab (polluted) andWadi Thall (unpolluted).

Each value is the mean±S.E. of three replicates.*indicates significant difference of the control at least at 5% level.ND: not detected, possibly its level was under the spectrophotometer sensitivity.

Table 3. Effect of heavy metal pollution on anitioxidant enzyme activities and lipid peroxidation (MDA concentration) oftwo Zygophyllum species grown in Ras Malaab (polluted) and Wadi Thall (unpolluted).

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Morsy et al.EurAsian Journal of BioSciences 6: 1-10 (2012)

Plasma membrane lipids

Total lipids, total phospholipids, total glycolipids

and total sterols were significantly decreased in

both species grown in polluted soil, the effect was

more pronounced in Z. coccineum (Table 4). Previous

published results indicated that copper and

cadmium stress decreased the total lipids,

phospholipids, glycolipids and sterols in pea

(Quartacci et al. 2000) pepper (Jemal et al. 2000) and

cucumber (Janicka et al. 2008).

Remarkable changes in the root PM

phospholipids (Table 5) and free fatty acids (Table 6)

were found in plants grown in polluted area. A

significant increased in PE was observed in the two

Zygophyllum species with a reduction in the PG and

PI contents, whereas the increase in PC was

insignificant (Table 5). The response of PS to heavy

metal pollution was varied in both species: it

increased in Z. coccineum while it was decreased in Z.

album. Heavy metal stress decreased PC/PE ratio in

both species, the decrease was greater in Z. album.

The reduction in PC/PE ratio may influence the

plasma membrane performance under pollution,

because PC and PG have membrane stabilizing

effect relative to PE (Thompson 1992, Mansour et al.

1994, Salama et al. 2007). Our finding supports

previous published data where copper and cadmium

stress increased PE while they reduced PG content in

Zea mays (Chaffai et al. 2005, Chaffai et al. 2009).

Increased PE might have an adaptive value to

counterbalance the membrane rigidifying impact of

increasing saturated fatty acids (Thompson 1992,

Mansour et al. 1994, 2002, Salama et al. 2007)

induced in the current study under heavy metal

stress (Table 6).

The root PM unsaturated fatty acids (18:1, 18:2

Table 4. Effect of heavy metal pollution on the root PM total lipids, total sterols, total glycolipids and total phospholipidsof two Zygophyllum species grown in Ras Malaab (polluted) and Wadi Thall (unpolluted).

Table 5. Effect of heavy metal pollution on the root PM phospholipid composition (nmol g-1) and PC/PE ratio of twoZygophyllum species grown in Ras Malaab (polluted) and Wadi Thall (unpolluted).

Table 6. Effect of heavy metal pollution on the root PM fatty acid composition (mol %) and saturated/unsaturated ratio oftwo Zygophyllum species grown in Ras Malaab (polluted) and Wadi Thall (unpolluted).

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Morsy et al.EurAsian Journal of BioSciences 6: 1-10 (2012)

Anonymous (1986) Council directive on the protection of the environment, and in particular of the soil, when sewagesludge is used in agriculture. Official Journal of the European Community, L181/6.

Beak KH, Skinner DZ (2003) Alteration of antioxidant enzyme gene expression during cold acclimation of near-isogenicwheat lines. Plant Science 165: 1221-1227. doi: 10.1016/S0168-9452(03)00329-7

Ben Ammar W, Nouairi I, Zorrouk M, Jemal F (2007) Cadmium stress induces changes in the lipid composition andbiosynthesis in tomato (Lycopersicon esculentum Mill.) leaves. Plant Growth Regulation 53: 75-85. doi:10.1007/s10725-007-9203-1

Black CA (1965) Methods of soil analysis. Parts 1 & 2, American Society of Agronomy, Madison, Wisconsin.Breckle SW, Kahle H (1991) Geobotany and ecology. Progress in Botany 52: 391-406.Candan N, Tarhan L (2003) The correlation between antioxidant enzyme activities and lipid peroxidation levels in

Mentha pulegium organs grown in Ca2+, Mg2+, Cu2+, Zn2+ and Mn2+ stress conditions. Plant Science 163: 769-779.doi: 10.1016/S0168-9452(03)00269-3

Chaffai R, Ali T, Ferjani E (2005) Comparative effects of copper and cadmium on growth and lipid content in maizeseedlings (Zea mays L.). Pakistan Journal of Biological Sciences 8 (4): 649-655. doi: 10.3923/pjbs.2005.649.655

Chaffai R, Seybon TN, Marzouk B, Ferjani E (2009) A comparative analysis of fatty acidcomposition of root and shootlipids in Zea mays under copper and cadmium stress. Acta Biologia Hungarian 60: 109-125. doi:10.1556/ABIOL.60.2009.1.10

Chinoy JJ, Singh YD, Gurumurti K (1976) Colorimetric determination of ascorbic acid turnover in plants. Indian JournalPlant Physiology 19: 122-30.

Ciemense S (2001) Molecular mechanisms of plant metal tolerance and homeostasis. Planta 212: 475-480. Deinstrop EH, Weinheim W (2000) Applied thin layer chromatography. Scottish Crop Research Institute, Dundee.Devi SR, Prasad MN (1998) Copper toxicity in Ceratophyllum demeresum, a free floating macrophyte: response of

antioxidant enzymes and antioxidants. Plant Science 138: 157-165.

and 20:1) was reduced whereas the saturated fatty

acids (14:0, 16:0) was increased in both species

under soil pollution (Table 6). This change in PM

fatty acid abundance lead to increased sat/unsat

ratio in the PM of both species, the effect was more

pronounced in Z. album. A decrease in fatty acyl

unsaturation of the PM under heavy metal pollution

has been also reported in wheat (Quartacci et al.

2000), Brassica juncea (Nouairi et al. 2006) and

tomato (Ben Ammar et al. 2007). The effect of fatty

acid saturation may be counterbalanced by the non-

significant increase in the PM PC, since PC increases

membrane lamellar structure and stability

(Thompson 1992, Mansour et al. 1994, 2002, Nouairi

et al. 2006, Ben Ammar et al. 2007, Salama et al.

2007). An increase in the degree of fatty acid

saturation is a typical reaction of plant PM to

different environmental stresses. In addition, certain

changes in the membrane lipids were reported to be

an adaptive response to different environmental

stresses, in order to restore optimum physical

membrane properties (Devi and Prasad 1999,

Mansour et al. 1994, 2002, 2003, Mansour and

Salama 2004, Nouairi et al. 2006, Ben Ammar et al.

2007, Salama et al. 2007). This appears to be the case

in the current work, where some PM lipid changes

might maintain membrane integrity under heavy

metal stress.

In conclusion, industrial activities increased the

level of heavy metals in the soil of Ras Malaab, which

resulted in drastic increase of shoot heavy metals of

both species. Accumulated heavy metals induced

oxidative stress in both species. Both Zygophyllum

species alleviated oxidative stress via increased

antioxidant enzyme activities. The root PM lipid

composition of Zygophyllum species was altered in

response to heavy metal pollution. Some of the PM

lipid changes might be in the favorable direction to

restore optimum membrane properties and

functions. Increased antioxidant enzyme activities as

well as PM lipid alterations might thus enable both

Zygophyllum species to withstand the prevailing

stressful environment.

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Ağır Metallerin, Zygophyllum Türlerinin Plazma Zarları ve Antioksidan EnzimleriÜzerine Etkisi

ÖzetGiriş: Ağır metaller, toprakta yüksek konsantrasyonlarda bulunduklarında, büyük çevresel kirleticilerdir ve bitkilerinbüyüme ve gelişimi üzerinde toksik etkileri vardır. Endüstriyel aktiviteler, çok geniş alanlarda ağır metallerin birikmesive doğal bitki örtüsünün etkilenmesini netice vermektedir. Bu yüzden, bitkilerin ağır metallerin olumsuz etkileri ilenasıl başa çıktıklarının anlaşılması çok büyük önem arzetmektdir.Materyal ve Metot: İki farklı alan seçildi. Bunlardan biri, bir alçıtaşı fabrikası yakınlarında, diğeri ise fabrikadan 25 kmuzaklıktaydı. İki Zygophyllum türü (Z. album ve Z. coccineum) çalışma alanlarında doğal olarak yetişmekteydi. Topraktakiağır metal stresinin; sürgün ağır metal konsantrasyonu, lipid peroksidasyonu, antioksidan enzim aktiviteleri ve kökplazma zarı (PM) lipid kompozisyonu üzerine etkileri analiz edildi.Bulgular: Çevre kirliliğine maruz kalan alanda yetişen her iki türün sürgünlerinde, ağır metal konsantrasyonları ve lipidperoksidasyonu arttı. Kirlilik şartları altında, her iki türde de; askorbat oksidaz (ASO), gayakol (GPX), askorbatperoksidaz (APX) ve süperoksit dismutaz (SOD) aktiviteleri artarken, katalaz (CAT) aktiviteleri azaldı. Z. album ve Z.coccineum'da PM toplam lipidleri, fosfolipidler, glikolipidler ve steroller azaldı. Ağır metal stresi; her iki türün kökPM'ında fosfatidiletanolamini (PE) artırdı, fosfatidilinositol (PI) ve fosfatidilgliserolü (PG) azalttı, fosfatidilkolinde (PC) iseönemli bir değişiklik oluşturmadı. Fosfatidilserin; kirlilik koşullarında, Z. album PM'ında (PS) azalırken, Z. coccineumPM'ında arttı. Ağır metal stresi, kök PM'ındaki yağ asitlerinin kompozisyon ve konsantrasyonunu değiştirdi ve her ikitürde doymuş/doymamış oranının değişmesine yol açtı.Sonuç: Zygophyllum türlerinin ağır metal stresine dayanabilmesi için, etkin bir antioksidan mekanizmasının ve olumluPM lipid dengesinin önemli olduğunu göstermektedir.

Anahtar Kelimeler: Ağır metal, antioksidan enzim, lipid peroksidasyonu, plazma zarı yagı, yağ asidi, Zygophyllum sp.