ORIGINAL PAPER

Differential responses to drought stress in leaves and roots of wildjujube, Ziziphus lotus

Mouna Maraghni • Mustapha Gorai •

Mohamed Neffati • Marie Christine Van Labeke

Received: 19 March 2013 / Revised: 13 December 2013 / Accepted: 16 December 2013

� Franciszek Gorski Institute of Plant Physiology, Polish Academy of Sciences, Krakow 2013

Abstract The aim of this study was to investigate the

effects of drought stress induced by polyethylene glycol-

6000 in wild jujube, Ziziphus lotus. One-month-old,

hydroponically grown seedlings were subjected to three

treatments, i.e. normal watering (-0.2 MPa), moderate

(-1.2 MPa) and severe (-2.1 MPa) drought stress for

14 days under controlled climatic conditions. Plant growth

was markedly reduced with increasing osmotic stress. The

shoot water potential (Ww) and leaf relative water content

followed similar patterns and significantly decreased with

increasing osmolality of solutions. As a consequence of

drought, contents in proline and soluble sugars were found

to be more elevated in leaves than in roots. The level of

lipid peroxidation in terms of malonyldialdehyde contents

increased in both leaves and roots of drought-stressed

plants. Wild jujube displayed higher activities of antioxi-

dant enzymes in the roots than in the leaves. Catalase and

guaiacol peroxidase activities increased significantly in

drought-stressed roots, whereas ascorbate peroxidase

activity showed a slight decline with no significant

changes. These findings suggest that Z. lotus was able to

adapt to severe drought stress by accumulation of com-

patible solutes and by activation of free radical-scavenging

enzymes. Overall, defence mechanisms in Z. lotus against

oxidative stress are organized differently in plant tissues,

with higher solute accumulation in leaves and increased

activity of antioxidants in roots, during drought stress.

Keywords Ziziphus lotus � Drought � Growth � Water

relations � Osmotic adjustment � Oxidative stress

Abbreviations

APX Ascorbate peroxidase

CAT Catalase

DM Dry mass

MDA Malondialdehyde

FM Fresh mass

PEG Polyethylene glycol

POD Guaiacol peroxidase

RWC Relative water content

Ww Water potential

TM Turgid mass

Introduction

Ziziphus species are sclerophyllous evergreen trees or

shrubs with a high degree of drought tolerance. Several

reports have investigated their physiological and morpho-

logical adaptations to water deficit stress (e.g. Clifford

et al. 1998; Arndt et al. 2001; Kulkarni et al. 2010; Mar-

aghni et al. 2011). The ability of Ziziphus species to survive

drought has been attributed to a combination of avoidance

Communicated by G. Bartosz.

M. Maraghni � M. Neffati

Laboratoire d’Ecologie Pastorale, Institut des Regions Arides,

4119 Medenine, Tunisia

M. Gorai (&)

Departement des Sciences de l’Environnement, Institut

Superieur de Biologie Appliquee de Medenine,

4119 Medenine, Tunisia

e-mail: gorai.mustapha@yahoo.fr

M. C. Van Labeke

Department of Plant Production, Faculty of Bioscience

Engineering, Ghent University, Coupure links 653,

9000 Ghent, Belgium

123

Acta Physiol Plant

DOI 10.1007/s11738-013-1473-9

and tolerance mechanisms, including osmotic adjustment

and stomatal control (Arndt et al. 2001; Pareek 2001;

Maraghni et al. 2011). Z. lotus is a native species of the

Mediterranean region and indigenous to Tunisia where it

has a wide ecological and geographical distribution and

grows under a variety of environmental conditions (Gorai

et al. 2010). It reaches 2–5 m, is dormant from October

through March, flowers in May and June, and produces

fruits in August (Gorai et al. 2010). The fruits, subglobose

drupes (c. 1–1.5 cm in diameter), are the edible part of the

plant (Maraghni et al. 2010). This spiny shrub is of great

economic and ecological interest: it stabilizes sand dunes,

and has food, feed, fuel and medicinal uses (Le Floc’h

1983; Borgi et al. 2008; Borgi and Chouchane 2009; Gorai

et al. 2010; Maraghni et al. 2010).

Drought is the major factor limiting crop production

worldwide (Ludlow and Muchow 1990). Therefore, phys-

iological and biochemical adaptations involved in cellular

and whole plant responses to drought generate considerable

interest. A very common response to drought is an

increased production of compatible organic solutes such as

soluble sugars, sugar alcohols, proline and betaines (Serraj

and Sinclair 2002). These compatible solutes contribute to

cellular osmotic adjustment, detoxification of reactive

oxygen species, protection of membrane integrity, and

stabilization of enzymes/proteins (Bohnert and Jenson

1996; Attipali et al. 2004).

Drought stress promotes the production of reactive

oxygen species (ROS), such as superoxide (�O2-), singlet

oxygen (O2� ), hydrogen peroxide (H2O2), and hydroxyl

radicals (OH�-) in plants. In higher plants, ROS are con-

tinuously produced in chloroplasts, mitochondria and per-

oxisomes (Apel and Hirt 2004). However, H2O2 produced

in peroxisomes and chloroplasts diffuses to the cytosol and

is converted to hydroxyl radicals by the Fenton reaction

(Moller et al. 2007). Overproduction of ROS in plant cells

under stress can damage cellular components, including

DNA, proteins and membrane lipids, and leads to destruc-

tion of photosynthetic pigments (Yordanov et al. 2000;

Mittler 2002). Different abiotic stress factors may induce

oxidative stress in plants, which lead to similar cellular

adaptive responses such as accumulation of compatible

solutes, induction of stress proteins and acceleration of

ROS-scavenging systems (Zhu 2002). To scavenge reactive

oxygen species, plants have evolved both enzymatic and

non-enzymatic defence systems (Ingram and Bartels 1996).

The non-enzymatic systems include b-carotenes, a-

tocopherol, ascorbate, glutathione and the enzymatic anti-

oxidants including superoxide dismutase (SOD), catalase

(CAT), ascorbate peroxidase (APX), guaiacol peroxidase

(POD) and glutathione reductase (GR) (Sofo et al. 2007).

ROS is converted by SOD into H2O2, which is further

scavenged by CAT and various peroxidases (APX, POD) to

H2O (Noctor and Foyer 1998). Oxidative stress increases

lipid peroxidation, forming adducts to deoxyguanosine and

deoxyadenosine (Marnett 1999). Under drought conditions

the behaviour of various shrubs indicated that activities of

antioxidant enzymes are correlated with their tolerance to

abiotic stress (Dichio et al. 2002; Sofo et al. 2004; Guo et al.

2006). Plant physiological processes, such as osmotic

adjustment and activities of antioxidant enzymes, depend

on the rapidity, severity and duration of the drought

(DaCosta and Huang 2007).

Involvement of antioxidant defence mechanisms against

water deficit stress was not studied in Z. lotus. Hence, this

study is the first report in this respect and aims to under-

stand the physiological and biochemical processes under-

lying differential tolerance to drought. We evaluated the

changes in growth parameters, water relations, lipid

membrane peroxidation (MDA), osmotic adjustment (pro-

line and soluble carbohydrates), and activity of three

antioxidant enzymes: CAT, APX, and POD.

Materials and methods

Plant material and drought stress applications

The experiments were carried out at the Faculty of Bio-

science Engineering—Ghent University, Ghent, Belgium.

Mature fruits were collected in September 2009 from

plants in natural Z. lotus populations growing at Samaaliate

(33�170N, 10�550E; Ben Guerdane, Southeast Tunisia).

Seeds were provided by the seed bank of the Laboratoire

d’Ecologie Pastorale at the Institut des Regions Arides,

Medenine, Tunisia. Seeds were disinfected in an aqueous

solution of calcium hypochlorite 5 % for 5 min, sown in

alveolar plates filled with loam and placed at controlled

conditions (Maraghni et al. 2010). When the cotyledons

were exposed, seedlings were transplanted in PVC pot

(8 9 7 cm). The temperature was maintained at 25/30 �C

(night/day), the level of photosynthetically active radiation

was 250 lmol m-2 s-1 and the day time humidity was

between 60 and 70 %. The plants were hydroponically

grown with standard Hewitt’s (1966) nutrient solution

using a circulating system (Fig. 1). This nutrient solution

contains following macronutrients: 1.5 mM MgSO4,

1.6 mM KH2PO4, 0.4 mM K2HPO4, 3 mM KNO3, 2 mM

NH4NO3, 3.5 mM Ca (NO3)2, and micronutrients: 8 lM

MnCl2, 0.7 lM CuSO4 5H2O, 0.76 lM ZnSO4 7H2O,

0.3 lM Mo7O24(NH4)6, 46 lM H3BO3 (Arnon and Hoa-

gland 1940) and 45 lM EDTA-Fe (Jacobson 1951). The

pH of the nutrient solution was daily adjusted to 6. Each

reservoir feeds two channels by pipes in which each

channel has 20 seedlings and was equipped with two tubes

of bubbling air, allowing good aeration.

Acta Physiol Plant

123

The experiment was arranged in a growth chamber in a

completely randomized design with three levels of drought

treatment 9 40 replicates. One-month-old seedlings were

supplied with PEG solutions at varying water potentials of

-0.2 MPa (control), -1.2 MPa (moderate stress) and

-2.1 MPa (severe stress) for 14 days. The concentration of

PEG-6000 in the nutrient solution needed to obtain the

respective drought stress levels was determined following

Michel and Kaufmann (1973) and adjusted using a Wescor

vapour pressure osmometer (model C-52 5500, Logan, UT,

USA).

Growth parameters

After 2 weeks of culture under different drought treatments,

shoots and roots were separated. Number of leaves and fresh

weights of shoots and roots were determined. Leaves and

roots were frozen in liquid nitrogen and blended using a

mortar and pestle previously chilled with liquid nitrogen.

The frozen powder was stored at -80 �C until analysis.

Plant water relations

Plant water status was evaluated by measuring water

potential (Ww) using a Scholander pressure chamber (PMS

Instruments co., Corvallis, R, USA) and relative water

content RWC = (FM - DM)/(TM - DM) 9 100, where

FM, DM and TM are the fresh, dry and turgid masses,

respectively. Wild jujube leaves were weighed immedi-

ately on harvest to determine FM. Turgid mass was

determined after leaves had been immersed for 24 h in

distilled water. After the determination of TM, leaves were

oven-dried at 80 �C for 48 h and DM was determined.

Determination of contents in proline, soluble

carbohydrates and starch

Free proline content was quantified as described by Bates

et al. (1973). Root and leaf samples (0.5 g) from each group

were homogenized in 3 % (w/v) sulphosalicylic acid and

homogenate was filtered through filter paper. After addition

of acid ninhydrin and glacial acetic acid, resulting mixture

was heated at 100 �C for 1 h in water bath. Reaction was then

stopped in ice. The mixture was extracted with toluene, and

the absorbance was read at 520 nm. Proline concentration

was determined using a calibration curve and expressed as

lmol proline g-1 FM.

Sugars from leaves and roots were extracted with 80 %

ethanol at 70 �C, and centrifuged at 5,0009g for 10 min.

Glucose, fructose and sucrose were analysed using high-pH

anion-exchange chromatography with pulsed amperometric

detection (Waters; CarboPac MA1 column with companion

guard column, eluent: 50 mM NaOH, 22 �C). The residual

ethanol insoluble material was washed twice with ethanol

80 % and the residue was treated with HCl 1 M for 2 h at

95 �C for starch hydrolysis. Starch was determined spec-

trophotometrically at 340 nm by the enzymatic reduction

of NADP?.

Extraction of malondialdehyde

The degree of lipid peroxidation was used to calculate

membrane integrity. Malondialdehyde (MDA) content was

measured as described by Hudges et al. (1999) with some

adaptations. 0.5 g aliquot of frozen powder was added to

1 ml of 0.1 % (w/v) trichloroacetic acid (TCA). The

homogenate was centrifuged at 3,0009g for 5 min. A 1-ml

aliquot of supernatant was added to 4.0 ml of 0.5 % (w/v)

thiobarbituric acid (TBA) in 20 % (w/v) trichloroacetic acid.

The mixture was heated at 100 �C for 30 min and then

quickly cooled in ice. After centrifugation at 3,0009g for

10 min, the absorbance of the supernatant at 600, 532 and

440 nm were determined. MDA content was calculated

using an absorption coefficient, e = 157 mM-1 cm-1 and

expressed as nmol MDA g-1 FM.

Enzyme extractions and assays

For protein and enzyme extractions, 0.5 g of leaf and root

samples was homogenized with 50 mM potassium phos-

phate buffer (pH 7.8) containing 1 mM EDTA-2Na and 7 %

(w/v) polyvinylpolypyrrolidone (PVPP). The whole extrac-

tion procedure was carried out at 4 �C. Homogenates were

Fig. 1 Experimental setup to study the response of Z. lotus seedlings

to water deficit induced by PEG at varying water potentials (-0.2,

-1.2 or -2.1 MPa) in nutrient solution under controlled cli-

matic conditions, a and b

Acta Physiol Plant

123

then centrifuged at 4 �C for 15 min at 13,0009g, and

supernatants were used for determination of enzyme activity.

Protein concentration was determined according to Bradford

(1976), using bovine serum albumin as a standard.

Catalase (CAT) activity (EC 1.11.1.6) was determined

using the method of Aebi (1984) with slight modification

by measuring the rate of decomposition of H2O2

(e = 2.3 mM-1 cm-1) at 240 nm. This activity was

assayed in a reaction mixture containing 1,900 ll of

potassium phosphate buffer (50 mM, pH 7.0 not containing

EDTA), 100 ll sample and 1,000 ll H2O2 (30 mM). CAT

activity is expressed as lmol H2O2 decomposed

min-1 mg-1 proteins.

Ascorbate peroxidase (APX) activity (EC 1.11.1.11)

was quantified as described by Nakano and Asada (1981).

The reaction mixture contained 50 mM of potassium

phosphate buffer (pH 7.0), 4.4 ll ascorbate (1 mM) and

10 ll EDTA-2Na (0.5 M). Adding H2O2 started the reac-

tion and the decrease in absorbance at 290 nm. Activity

was calculated using the extinction coefficient,

e = 2.8 mM-1 cm-1. Each sample was measured in trip-

licate. APX activity is expressed as lmol oxidized ascor-

bate min-1 mg-1 proteins.

Guaiacol peroxidase (POD) activity (EC 1.11.1.7) was

assayed by the method of Chance and Maehly (1955). The

reaction mixture with a final volume 1 ml contained 700 ll

of 0.05 M phosphate buffer (pH 7.8), 100 ll of plant extract

and 200 ll of guaiacol (25 mM). To start the reaction, 100 ll

of H2O2 was added. The increase of absorbance due to oxi-

dation of guaiacol to tetraguaiacol was monitored for 3 min

at 436 nm. Activity was calculated using the extinction

coefficient, e = 25.5 mM-1 cm-1. POD activity is expres-

sed as lmol oxidized guaiacol min-1 mg-1 proteins.

Statistical analysis

Data were analysed using SPSS statistical software version

17.0. All measurements were subjected to analysis of

variance (ANOVA) and differences among treatments were

compared by Tukey’s HSD test at the level of significance

P = 0.05.

Results

Growth attributes

Increasing drought stress, induced by PEG, significantly

decreased the growth attributes of Z. lotus seedlings

(Table 1; P \ 0.001). The number of leaves decreased

significantly by 54 and 75 % as compared to the controls

for moderate and severe stress, respectively. Fresh mass

was considerably reduced under severe drought stress in

both shoots and roots (ca. 76 and 69 % of the control value,

respectively).

Water relations

As shown in Fig. 2a, the shoot Ww decreased significantly

(P \ 0.001) by increasing the osmolarity of the growing

solutions. At the highest PEG concentration, shoot Ww

Table 1 Number of leaves, and root and shoot fresh mass (mg FM

plant-1) of Ziziphus lotus when 1-month-old plants were subjected for

14 days to water deficit induced by PEG at varying water potentials

(-0.2, -1.2 or -2.1 MPa) in nutrient solution

Water potential

(MPa)

Number of

leaves

Shoot FM Root FM

-0.2 44.89 ± 6.63 a 1.29 ± 0.16 a 0.52 ± 0.08 a

-1.2 20.67 ± 3.85 b 0.54 ± 0.10 b 0.42 ± 0.12 ab

-2.1 11.00 ± 1.92 b 0.31 ± 0.04 b 0.16 ± 0.02 b

Mean ± SE (n = 9) within a column followed by the same letter are

not significantly different at the 0.05 probability level

Fig. 2 Changes in a shoot water potential (Ww, MPa), and relation-

ship between b shoot water potential and leaf relative water content

(RWC, %) of Z. lotus. One-month-old plants were subjected for

14 days to water deficit induced by PEG at varying water potentials in

nutrient solution. A Line describing the dependency was obtained

using polynomial regression and values are from three treatments

with four replicates (n = 12). Data represent mean ± SE, n = 3.

Bars with different letters are significantly different among treatments

(P \ 0.05, Tukey’s test)

Acta Physiol Plant

123

dropped to -2 MPa. RWC had a decreasing trend as Ww of

growth solutions dropped. This parameter decreased from

83 % for control leaves to 78 and 69 % for drought-stres-

sed leaves under moderate and severe stress, respectively.

The relationship between shoot Ww and the leaf RWC

changed significantly in drought-stressed plants versus

control plants (Fig. 2b).

Solute accumulation

Ziziphus lotus seedlings in the presence of PEG-enriched

nutrient solution accumulated higher amounts of proline in

the leaves than in the roots (Fig. 3, P \ 0.001). When

subjected for 14 days to moderate and severe water deficit

stress, the leaves accumulated 12- and 19-fold, respec-

tively, more proline than controls.

Plants accumulated higher soluble sugars (glucose,

fructose and sucrose) contents in leaves than in roots

(Fig. 4a–c). On day 14 of severe drought stress, glucose

and fructose contents in leaves changed significantly

compared to the controls; however, those in roots remained

unchanged and were not statistically significant. At low

water potential of the growth medium (-2.1 MPa), the

sucrose fraction increased either in leaves or roots (ca. 173

and 400 % of the control value, respectively). Starch

content changed significantly in 14-day drought-stressed

plants at Ww = -2.1 MPa of nutrient solution. This con-

tent increased in roots but decreased in leaves (Fig. 4d).

Lipid peroxidation

As seen in Fig. 5, lipid peroxidation, measured as MDA

content, increased significantly in the leaves and roots of

treated plants versus the controls. At 14 days of severe

drought stress, MDA content was increased by six and

sevenfold in roots and leaves, respectively, as compared to

the controls.

Enzyme activities

The activity of catalase was higher in roots than in leaves,

whatever the PEG dose in the nutrient solutions. The

increase of PEG-osmolarity enhanced the activity of CAT

in roots, while no significant changes were observed in the

leaves (Fig. 6a). CAT activity was increased 1.5- and 2.1-

fold at water potentials of -1.2 and -2.1 MPa in nutrient

solution, respectively, as compared to controls.

Most changes in APX activity for drought-stressed roots

versus the controls were not statistically significant

(Fig. 6b). At all water potentials, APX activity in leaves

was lower than in roots. APX activity remained unchanged

under moderate drought (-1.2 MPa), whereas it was sig-

nificantly reduced in both organs under severe drought

(-2.1 MPa), as compared to controls.

High values of POD activity were recorded in the roots.

At water potential of -2.1 MPa of nutrient solution, POD

activity was induced significantly in roots (2.1-fold), while

it was inhibited significantly in leaves (4.7-fold), as com-

pared to the controls (Fig. 6c).

Discussion

The present study shows that the osmotic potential of the

solution induced by PEG reduced the growth of Z. lotus by

restricting leaf formation and biomass production. This

response has been reported in several species subjected to

drought, like Z. mauritiana (Clifford et al. 1998), Z. ro-

tundifolia (Arndt et al. 2001), Olea europaea (Bacelar et al.

2007) and Adansonia digitata (De Smedt et al. 2012). The

drought-induced growth reduction might be related to

accelerated senescence of older leaves and reduction of

their size. For instance, Larcher (2003) showed that small

leaves are a characteristic for plants growing in dry envi-

ronments. Several authors have reported the strong impli-

cation of the root elongation and the ability to shed leaves

on Ziziphus species in extremely hot and arid environments

(Sankhla 1998; Jones 1999). Ziziphus species are typical

phreatophytes and behaves as arido-active species (Gorai

et al. 2010) throughout dry seasons.

Our data show a significant decrease in leaf RWC and

shoot Ww with increasing osmolality of solutions. These

changes may also result in stomatal closure, reduction of

CO2/O2 ratio in leaves and CO2 assimilation (Gindaba

et al. 2004; Boussadia et al. 2008). Maintaining leaf RWC

under lower shoot Ww is an important adaptation exhibited

by Z. lotus to cope with extreme drought conditions. The

present data agree with findings reported on Z. mauritiana

(Clifford et al. 1998), Z. rotundifolia (Arndt et al. 2001)

and Z. mauritiana (Kulkarni et al. 2010).

Fig. 3 Changes in leaf proline content (lmol g-1 FM) of Z. lotus.

One-month-old plants were subjected for 14 days to water deficit

induced by PEG at varying water potentials in nutrient solution. Data

represent mean ± SE, n = 3. Bars with different letters are signif-

icantly different among treatments (P \ 0.05, Tukey’s test)

Acta Physiol Plant

123

On the other hand, proline accumulation in Z. lotus was

more pronounced in leaves than in roots under water deficit

stress. At the lowest Ww (-2.1 MPa), leaf proline accu-

mulation was 19-fold higher than that of control conditions.

This is in agreement with findings of Choudhary et al.

(1996) and Clifford et al. (1998) who reported a similar

response in other species of the genus Ziziphus under

osmotic stress. For instance, Sundaresan and Sudhakaran

(1995) mentioned that water stress induced by PEG

(-1.65 MPa) caused a 25-fold increase in proline levels in

young excised leaves of the susceptible cultivar of cassava

(M-4), while the increase was about ninefold in the tolerant

cultivar (S-1215).

Leaves accumulated soluble sugars at higher levels than

roots, as signs of osmotic adjustment with increasing PEG-

osmolality. Sucrose, glucose and fructose accounted for the

vast majority of change in sugars and sucrose content was

higher than other osmolytes. According to Arndt et al.

(2001), the decreased demand for carbon caused by low

photosynthetic rates in drought-stressed leaves contributes

to the increase of soluble sugars concentrations. Starch

accumulation decreases in leaves of Z. lotus, whereas it

increases in roots as osmotic stress intensified. Clifford

et al. (1998) reported that decrease in leaf starch content of

Z. mauritiana could account for the increase of hexose

concentration (64 %) under drought stress. Interestingly,

starch degradation could be increased under water deficit as

b-amylase activity increased (Todaka et al. 2000). How-

ever, high starch concentrations in roots are strongly cor-

related with carbon allocation to roots under water deficit

as shown by Arndt et al. (2000, 2001) for Z. mauritiana and

Z. rotundifolia, respectively.

Osmotic adjustment by net accumulation of solutes in

cells in response to a fall in the water potential of their

environment can in part offset this deterioration of growth

conditions. As a consequence of this net accumulation, the

cell osmotic potential is lowered, and turgor pressure tends

to be maintained (Blum et al. 1996). In our experiments,

shoot Ww becomes more negative with increasing osmo-

lality of the nutrient solution. Thus, turgor could be

maintained, and obviously the osmotic adjustment was

sufficient to compensate the reduction in shoot Ww in plants

growing under dry conditions.

The ROS level during drought stress may indicate the

occurrence of oxidative stress in plants (Foyer and Noctor

2005). Lipid peroxidation is an indicator of oxidative dam-

age under water stress conditions and is one of the most

Fig. 4 Changes in a glucose

(lmol g-1 FM), b fructose

(lmol g-1 FM), c sucrose

(lmol g-1 FM) and d starch (g/

100 g FM) concentrations in

leaves and roots of Z. lotus.

One-month-old plants were

subjected for 14 days to water

deficit induced by PEG at

varying water potentials in

nutrient solution. Data represent

mean ± SE, n = 3. Bars with

different letters are significantly

different among treatments

(P \ 0.05, Tukey’s test)

Fig. 5 Changes in malondialdehyde content (MDA, nmol g-1 FM)

in leaves and roots of Z. lotus. One-month-old plants were subjected

for 14 days to water deficit induced by PEG at varying water

potentials in nutrient solution. Data represent mean ± SE, n = 3.

Bars with different letters are significantly different among treatments

(P \ 0.05, Tukey’s test)

Acta Physiol Plant

123

investigated ROS actions in membrane structure and func-

tion (Blokhina et al. 2003). The results showed that water

deficit reduces damage in cell membranes of Z. lotus by

accumulation of MDA. Different levels of lipid peroxidation

between root and leaf were found and higher MDA content

was found in leaves. The lower level of lipid peroxidation

marked in roots of stressed plants suggests a better protection

against oxidative damage. The evolution pattern in lipid

peroxidation for wild jujube plants is in agreement with

several species subjected to drought (Bacelar et al. 2006;

Turkan et al. 2005; Hassine and Lutts 2010).

Although several studies have been performed charac-

terizing Ziziphus species responses to drought, limited

information is available on the effect of water deficit stress

at the level of antioxidant enzyme system. The improved

protection in Z. lotus may reflect a more efficient antioxi-

dative system as evidenced by higher enzymes activities in

roots than leaves. The CAT activity remained almost

unchanged in drought-stressed leaves. These data are

similar to Bian and Jiang (2009) who reported no changes

in leaf CAT activity of Kentucky bluegrass under drought

stress and recovery. However, increased root CAT activity

in Z. lotus under water deficit stress is in agreement with

various studies (Sofo et al. 2004; Ben Ahmed et al. 2009).

The higher root CAT activity in Z. lotus would partly

explain the lower H2O2 concentration in the root, protect-

ing the organism against oxidative damage, in turn

enhancing drought tolerance.

The non-significant decrease of root APX activity indi-

cated an adaptive feature to PEG-induced osmotic stress in

Z. lotus. This promotes H2O2 accumulation, which could

result in hydroxyl radical formation; therefore, it explains

lipid peroxidation and starch accumulation to reduce oxi-

dative damage. This is consistent with response observed in

mycorrhizal Phillyrea angustifoli showing lower APX

activity in roots and shoots during drought (Porcel and

Ruiz-Lozano 2004).

Our data show that wild jujube increases root POD

activity under water deficit. This suggests that POD func-

tion as key enzymes that scavenge H2O2 in Z. lotus under

drought stress. According to Foyer et al. (1997), the dif-

ference in activation of POD, following water deficit

treatment, might indicate a physiologically different

response as oxidative stress develops. Similar to our find-

ings Bian and Jiang (2009) and Sofo et al. (2004) found

significant increase in root POD activity in drought-stres-

sed plants. Dichio et al. (2002) reported that an increase of

total POD activity during water deficit stress contributes to

the restriction in cell expansion, which in turn reduces

shoot growth.

An important relationship between drought tolerance

and antioxidant defence such as SOD, CAT, APX, under

water deficit has been reported in several studies (Schwanz

and Polle 2001; Sofo et al. 2004; Dichio et al. 2005). The

maintenance of a favourable balance between SOD, APX

and CAT is essential to avoid ROS accumulation, to pre-

serve the photochemical apparatus and to avoid significant

oxidative damage (Guo et al. 2007).

In conclusion, it is possible that defence against oxida-

tive stress is organized differently in Z. lotus, increasing the

solute accumulation in leaves and antioxidant enzymes in

roots. This might indicate that this shrubby species devel-

oped differential mechanisms as a function of organ type to

avoid oxidative damage produced during drought stress.

Author contribution Mouna Maraghni carried out all

experiments and analysis and drafted the initial version of

Fig. 6 Changes in the activities of three antioxidant enzymes in

leaves and roots of Z. lotus when one-month-old plants were

subjected for 14 days to water deficit induced by PEG at varying

water potentials in nutrient solution. a catalase (CAT), b ascorbate

peroxidase (APX) and c guaiacol peroxidase (POD). Data represent

mean ± SE, n = 3. Bars with different letters are significantly

different among treatments (P \ 0.05, Tukey’s test)

Acta Physiol Plant

123

the manuscript. Mustapha Gorai wrote part of the text,

prepared figures and was responsible for verification of

paper during the online submission. Mohamed Neffati

coordinated the study. Marie-Christine Van Labeke con-

tributed to the implementation of the study and manuscript

preparation.

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