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International Journal of Research in Plant Science 2012; 2(1): 1-7

ISSN 2249-9717

Original Article

Effect of NaCl Stress on Biochemical and Enzymes Changes of the Halophyte Suaeda

maritima Dum.

M. Rajaravindran and S. Natarajan*

Department of Botany, Annamalai university, Annamalainagar, Tamilnadu, India- 608 002

Email; s.natarajan20@yahoo.com

Received 01 February 2012; accepted 15 February 2012

Abstract

The present study was made to study the effect of different concentrations of sodium chloride on biochemical constituents and antioxidant enzymes of the seedlings of Suaeda maritima. The plant could survive a wide range of 100-500 mM NaCl

concentrations. The upper limit for the survival of the seedlings was 300 mM NaCl. Organic compounds such as amino acids

and sugar decreased upto optimum level of 300mM NaCl concentration. The starch and chlorophyll content increased upto

300mM NaCl. Beyond these levels the content decreased marginally. The proline content increased with the increasing

concentration of the salt. The antioxidant enzymes such as catalase (CAT), peroxidase (POX) and poly phenol oxidase (PPO)

increased up to the optimum level of 300mM NaCl concentration and beyond these levels the contents decreased marginally.

© 2011 Universal Research Publications. All rights reserved Key words: NaCl, Salinity,Halophytes,Organic constituents, antioxidant enzymes, Suaeda maritima

INTRODUCTION

Salinity stress is one of the most significant limiting

factors in agricultural crop productivity (Boyer, 1982).

Salinity and drought are among the major stresses that

adversely affect plant growth and crop productivity. These

constraints remain the primary causes of crop losses

worldwide, reducing average yields by more than 50%

(Boyer, 1982; Wang et al., 2003). Salt stress alters various

biochemical and physiological responses in plants, and thus affects almost all plant processes including photosynthesis,

growth and development (Iqbal et al., 2006).

Salt induces osmotic stress by limiting absorption of

water from soil, and ionic stress resulting from high

concentrations of potentially toxic salt ions within plant cells.

Plants have evolved a variety of protective mechanisms to

allow with these unfavorable environmental conditions for

survival and growth including the accumulation of ions and

osmolytes such as proline. The accumulation of these

compounds prevents water loss and ion toxicity. The

alleviation of oxidative damage and increased resistance to

salinity and other environmental stresses are often correlated

with an efficient antioxidative system (Jaleel et al., 2007 a,b;

Manivannan et al., 2007). Salinization of agricultural soils is

a worldwide concern, especially in irrigated lards. Saline soil

is characterized by the presence of toxic levels of sodium and

its chlorides and sulphates.

Salt tolerance is the ability of plants to grow and

complete their life cycle on a substrate that contains high

concentrations of soluble salt. Plants that can survive on high

concentrations of salt in the rhizosphere and grow well are called halophytes. Salinity tolerance is defined as the ability

of plants to continuously grow under salt stress conditions

(Munns, 2002).iAnother major factor of salt tolerance

mechanisms is the ability of plant cells to adjust osmotically

and to accumulate organic solutes (proteins, sugar, amino

acids, etc.). The accumulation of these compounds is not only

important for cell osmoregulation but also for the protection

of subcellular structure (Munns, 2002) and maintenance of

protein structures. Many of the physiological adaptations of

plants to saline conditions are similar to the adaptations

shown by plants to desiccation stress and it has been

suggested that plants showing drought resistance would also

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International Journal of Research in Plant Science

Universal Research Publications. All rights reserved

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International Journal of Research in Plant Science 2012; 2(1): 1-7

exhibit salinity tolerance (Munns, 2002). However, in some

halophytes, the salt tolerance mechanisms are not sufficient for

tolerance of drought or frost (Ueda et al., 2003). Halophytes and

other salt-tolerant plants may provide sensible alternatives for

many developing countries (Squires and Ayoub, 1994).

MATERIALS AND METHODS

Plant Materials and Treatments

Healthy seedlings of Suaeda maritima were up rooted

without damaging the root system and brought to the

laboratory in polythene bags. Uniform sized and healthy

seedlings after a through wash in the tap water were planted

individually in polythene bags (7 5). The polythene bags filled with homogenous mixture of garden soil containing red

earth, sand and farmyard manure (1:2:1). The seedlings were

irrigated with tap water and allowed to establish well. After

establishment in polythene bags for 30 days about 300

healthy plants were subjected to saline treatment. The

treatment constituted control, 100, 200, 300, 400 and 500

mM NaCl concentration. At higher concentrations, seedlings mortality occurred within a week after the salt treatment. The

experimental plants thereafter, maintained upto 500mM

NaCl. Salt solutions were prepared with NaCl (Laboratory

Grade, Glaxo Laboratories, India). The treatments were

continued until the plants received the required

concentrations of the salt, after this all the plants were

irrigated with tap water. The experimental yard was roofed

with transparent polythene sheet at the height of 3 m from the

ground in order to protect the plants from rain. Sampling for

various studies was taken on the 60th day after NaCl

treatment.

Estimation of total free amino acids Total free amino acid content was estimated by the

method Moore and Stein (1948), the leaf, stem and root

tissues were treated with 80 per cent boiling ethanol for

taking extracts (5 ml extract representing 1 g tissue). One ml

of ethanol extract was taken in 25 ml test tube and neutralized

with 0.1 N sodium hydroxide using methyl red indicator. One

ml of ninhydrin reagent was added (800 mg stannous chloride

in 500 ml citrate buffer pH, 5.0, 20 g ninhydrin in 500 ml

methylcellosolve, both solutions were mixed). The contents

were boiled in a water bath for 20 minutes and 5 ml of

diluting solution (distilled water and n-propanol mixed in equal volume) was added, cooled and diluted to 25 ml with

distilled water. The absorbance was measured at 570 nm in a

spectrophotometer (U-2001, HITACHI).

Estimation of total sugars

Total sugars were determined by Nelson (1944), One ml

of ethanol extract taken in the test tube was evaporated in a

water bath. To the residue, 1 ml of distilled water and 1 ml of

1 N sulphuric acid were added and incubated at 49C for 30 minutes. The solution was neutralized with 1N sodium

hydroxide using methyl red indicator. One ml of Nelson

reagent was added to each test tube prepared by mixing

reagent A and B in 25:1 ratio (Reagent-A: 25 g sodium

carbonate, 25 g sodium potassium tartarate, 20 g sodium

bicarbonate and 200 g anhydrous sodium sulphate in 1000

ml; Reagent – B: 15 g cupric sulphate in 100 ml of distilled

water with 2 drops of concentrated sulphuric acid). The test

tube were heated for 20 minutes in a boiling water bath, cooled and add 1 ml of arsenomolybdate reagent (25 g

ammonium molybdate, 21 ml concentrated sulphuric acid, 5 g

sodium arsenate dissolved in 475 ml of distilled water and

incubated at 37C in a water bath for 48 h) was added. The solution was thoroughly mixed and diluted to 25 ml and read

at 495 nm in a spectrophotometer. The reducing sugar

contents of unknown samples were calculated from glucose

standards.

Estimation of protein

Protein was assayed as described by Lowry et al.

(1951), to 0.5 ml of protein extract, 5 ml of the reagent C

was added (prepared by mixing reagent A and reagent B in

25:1 ratio; Reagent-A: 400 mg of NaOH was dissolved in distilled water and made upto 100 ml. To this solution, 2 g of

Na2CO3 was added. Reagent-B: 2 g of CuSO4 was dissolved in

distilled water and made upto 100 ml and 2 g sodium potassium

tartarate was dissolved in distilled water and made upto 100

ml, both solution were mixed equal volume) and it was allowed

to stand for 10 minutes at 28C. 0.5 ml of folin-phenol reagent (Folin-ciocalteu and distilled water were mixed in the ratio 1:2

(v/v)) was added to this solution and kept at room temperature

(30C) for 10 minutes and the absorbance was read at 660 nm in a spectrophotometer. The protein contents of unknown

samples were calculated from Bovine Serum Albumin

standards.

Estimation of proline

Proline was assayed according to the method Bates et al.

(1973). Five hundred mg of plant tissue was homogenized in 10 ml of 3 per cent aqueous sulphosalicylic acid. The

homogenate was filtered through Whatmann No. 42 filter

paper. Two ml of acid ninhydrin (1.25 g ninhydrin in 30 ml

of glacial acetic acid and 20 ml of

6 M phosphoric acid) and 2 ml of glacial acetic acid in a test

tube was heated for an hour at 100C. The reaction mixture was extracted with 4 ml of toluene and mixed vigorously by

using a vortex mixture for 15-20 seconds. The chromophore

containing toluene was aspirated from the aqueous phase.

The absorbance of the toluene layer was measured in a

spectrophotometer at 520 nm using toluene as blank.

Estimation of chlorophyll

Chlorophyll content was estimated by the standard method Arnon (1949). Five hundred mg of leaf tissue was

taken in a pestle and mortar with 10 ml of 80 per cent acetone

and it was ground well. Then the homogenate was

centrifuged at 800 g for 10 minutes and the supernatant was

saved. The pellet was re-extracted with 5 ml of 80 per cent

acetone each time till the pellet become colorless.

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International Journal of Research in Plant Science 2012; 2(1): 1-7

Estimtaion of catalase (EC 1.1.1.6)

Catalase activity was assayed as described Chandlee and

Scandalios (1984). 500 mg of frozen material was

homogenized in 5ml of ice cold 50 mM PMSF (Phenyl

methyl sulfonyl fluoride). The extract was centrifuged at 4ºC

for 20 min at 12500 rpm. The supernatant was used for enzyme assay. The activity of enzyme catalase was measured

using the method of Chandlee et al. (1984) with modification.

The assay mixture contained 2.6 ml of 50 mM potassium

phosphate buffer (pH 7.0), 0.4 ml of 15 mM H2O2 and 0.04

ml of enzyme extract. The decomposition of H2O2 was followed

by the decline absorbance at 240 nm. The enzyme activity was

expressed in units per min per mg protein.

Estimation of peroxidase (donor: hydrogen peroxide

oxidoreductase; (EC. 1.11.17)

Peroxidase activity was assayed by the method Kumar

and Khan (1982). Assay mixture of peroxidase contained 2ml

of 0.1 M phosphate buffer (pH 6.8), 1ml of 0.001M pyrogallol, and 1ml of 0.005M hydrogen peroxide and 0.5ml

of enzyme extract. The reaction mixture was incubated for 5

minutes at 25C, after which the reaction was terminated by adding 1ml of 2.5 N sulphuric acids. The amount of

purpurogallin formed was determined by reading the

absorbance at 420 nm against a blank prepared by adding the

extract after the addition of 2.5 N sulphuric acid at zero time.

The activity was expressed in unit per minute per mg protein.

Estimation of polyphenoloxidase (O-Diphenol: O2

oxidoreductase, EC. 1.10.3.1)

Polyphenol oxidase activity was assayed Kumar and

Khan (1982). Assay mixture for polyphenol oxidase

contained 2 ml of 0.1M phosphate buffer pH (6.0), 1ml of 0.1M catechol and 0.5 ml of enzyme extract. This was

incubated for 5 minutes at 25C, after which the reaction was stopped by adding 1ml of 2.5N sulphuric acid. The

absorbance of the purpurogallin formed was recorded at 495

nm. The enzyme activity was expressed in units. One unit is

defined as the amount of purpurogallin formed, which raised

the absorbance by 0.1 per minute under the assay condition.

Statistical analysis

Each treatment was analyzed with at least five replicates

and a standard deviation (SD) was calculated; data are

expressed in mean ± SD of five replicates.

RESULTS AND DISCUSSION

Effect of salinity on amino acid content

The results on the effect of NaCl salinity on the free

amino acid are presented (Fig. 1). The amino acid content of

the leaf, stem and root decreased with increasing NaCl

concentrations upto 300 mM in Suaeda maritima. Of the

three tissues the leaf had more amino acids then the other two

tissues. The total free amino acid content was found to

decrease gradually with increasing concentration of NaCl

treatment upto 300 mM respectively, and at higher

concentrations, there was a gradual increase in the amino acid

content. Greater accumulation of amino acids was also

observed in halophytic plants of Aeluropus logopoides and

Sporobolus madraspatanus in response to increased seawater

salinity in growth medium (Joshi and Misra, 2000). Similar

observations were made in other halophytes such as

Helochola setulasa (Joshi et al., 2002). A gradual increase in amino acid at high salinity level could be due to increased

degradation of protein. Proline was the most abundant amino

acid that increased with NaCl treatment in the plants.

Fig.1.Effect of NaCl on amino acid content (mg g-1 fr. Wt.) of Suaeda Maritima on 60th day qfter treatment.

Effect of salinity on protein content

Fig.2.Effect of NaCl on total sugar content (mg g-1 fr. wt.) of

Suaeda maritima on 60th day after treatment.

Changes in the protein content in the leaf stem and root

in response to different concentrations of NaCl are given in (Fig. 2). The protein content increased with increasing NaCl

salinity upto 300 mM in Suaeda maritima. And at higher

concentrations it steadily declined. The changes in soluble

protein showed a reverse trend to that of free amino acids

implying that the increase in protein content may be at the

expense of amino acids and that the salinity changes

influenced the inter conversion of these compounds. In

halophytes, the protein content increased with increasing

concentrations such as Helochola setulosa (Joshi et al.,

2002), and Thellanjiella halophila (M‟rah et al., 2006). In

general, the protein content increased with increasing concentration upto an optimal level. Beyond the optimum

level, the protein content decreased in Sesuvium portulacastrum

(Venkatesalu et al., 1994) and Helianthus annuus (Manivannan

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International Journal of Research in Plant Science 2012; 2(1): 1-7

et al., 2008). Protein content in the tissues of many plants

declined under drought or salinity stress, because of

proteolysis and decreased protein synthesis (Joshi and Misra,

2000).

Effect of salinity on sugar content

Changes in total sugar content in leaf stem and root in response to different concentrations of NaCl are given in

(Fig.3). The total sugar content decreased with increasing

concentrations upto 300mM NaCl. At higher concentrations,

total sugar content increased gradually. The total sugar

content had decreased with increasing NaCl salinity up to the

optimum level and at higher salinities the sugar content had

increased. The higher sugar content in the extreme salinity

levels is regarded as an additional mechanism to prevent salt

injury (Rathert, 1982). Under severe salinity stress, a low

carbohydrate level could be due to either high respiration or a

decrease in photosynthetic activity accompanied by reduction in

growth rate. The changes in the carbohydrate are regulation primarily by K+ and Cl- ions (Rathert, 1982). An increasing sugar

content and corresponding decrease in the starch at higher

salinities have been reported in several halophytes (Joshi et

al., 2002; Ashraf and Haris, 2004). Sugars are the source of

energy and carbons needed for adaptative or defensive

responses to stresses.

Fig.3.Effect of NaCl on protein content (mg g-1 fr. wt.) of

Suaeda maritima on 60th day after treatment.

Effect of salinity on proline content

The effect of NaCl on the proline content in the leaf,

stem and root are given in (Fig. 4). There was a gradual rise

in the level of proline in all the three tissues on 60th day sampling with increasing concentration of NaCl. The leaf

always had more proline than the stem and root. An

increasing accumulation of proline was found with increasing

concentrations of NaCl. The accumulation of proline was

more in the leaf tissues than in the stem and root tissues of

NaCl treated plants. The positive correlation exists between

the proline and salinity treatment. Salinity tolerance has been

associated with the capacity of a species to accumulate proline

and it acts as an intracellular osmoticum. Proline is believed to

function as compatible solute in balancing cytoplasmic and

vacuolar water potentials (Hassine et al., 2008). Generally salt

Fig.4. Effect of NaCl on proline content (mg g-1 fr. wt.) of

Suaeda maritima on 60th day after treatment

stress induces proline accumulation in many halophytes

(Brown and Pezeshki, 2007; Song et al., 2006).The present

observations are in accordance with several studies that

proline content progressively increased with high levels of

salinity in Thellungiella halophilla (Inan et al., 2004) and

Sesuvium portulacastrum (Ramani et al., 2006). Proline may act

as an enzyme protectant stabilizing the structure of

macromolecules and organelles. Recent studies indicate that

adaptation to salinity is closely associated with proline accumulation. A significant increase in proline content was

found only at high salinity salinity (Wang, 2006).

Effect of Salinity on chlorophyll content

Fig.5.Effect of NaCl on chlorophyll „a‟, chlorophyll „b‟ and total chlorophyll (mg g-1 fr. wt.) of Suaeda maritima on 60th day

after treatment.

An increasing trend in chlorophyll content of the leaf

was noticed (Fig.5) with increasing NaCl concentration upto

300mM NaCl on the 60th day of salt treatment and thereafter,

it steadily declined. The chlorophyll „a‟ was always higher

than that of chlorophyll „b‟ at all concentrations. The

chlorophyll content of Suaeda maritima was found to increase

with the increasing NaCl concentration upto 300 mM and at

higher concentrations of NaCl, there was a decrease in the

chlorophyll content. A decrease in the chlorophyll content

under salinity has been reported by several workers in a number of halophytes such as Avicennia sp. and Aegiceras

corniculatum (Shinde and Bhosale, 1985). The decrease of

chlorophyll is mainly attributed to the destruction of

chlorophyll “a‟ which is considered to be more sensitive to

salinity than chlorophyll “b” (Shinde and Bhosale, 1985).

Similar results have been reported for other halophytes that

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International Journal of Research in Plant Science 2012; 2(1): 1-7

increased the chlorophyll content with increasing salinity

upto an optimal level; Ipomoea pes-caprae (Venkatesan et

al., 1995) and Ceriops roxburghiana (Rajesh et al., 1998).

Effect of salinity on catalase Activity

The effect of NaCl on the catalase activity in the leaves

at various NaCl concentrations is presented in (Fig. 6). There was a steady increase in the enzyme activity with increasing

salinity upto 300mM in Suaeda maritima at higher

concentrations, the enzyme activity decreased. Enhanced

activity of catalase was reported to be essential for the

survival of the halophytes, Halimions portulacoides in natural

saline habitats (Kalir and Poljak off-Mayber, 1981). The

catalase activity increased with increasing concentration of

NaCl upto optimum level in Ipomoea pes-caprae

(Venkatesan and Chellappan, 1999). The catalase activity

decreased with increasing concentration in Phaseolus

radiatus (Saha and Gupta, 1999).

Fig.6. Effect of NaCl on catalase, peroxidase and

polyphenol oxidase activity (units min-1 mg-1 protein.) in the

leaf of Suaeda maritima on 60th day after treatment.

Effect of salinity on peroxidase activity

The peroxidase activity showed a similar increasing

trend as that of catalyse upto the optimum level of NaCl

salinity and data are given in (Fig. 6). The highest activity was recorded in Suaeda maritima at the optimum level

(300mM NaCl). Even at the extreme salinity the peroxidase

activity was equal to that of control. Increase in peroxidase

activity indicated the formation of large amount of H2O2 and

which could release enzyme from membrane structure

(Zhang and Kirkham, 1994). Peroxidase is a scavenging

enzyme which removes the toxic oxygen radicles from the

cells. Significant increase in the peroxidase activity in the

halophytes such as Aegiceras corniculatum (Manikandan and

Venkatesan, 2004), in the salt tolerant varieties of spinach

leaves (Oztiirk and Demir, 2003) and Xanthosoma sagittifolium (Kanmegne and omokoto, 2003). The increased peroxidase

activity was mainly due to increased enzyme synthesis and

might be useful for adaptation under conditions requiring

prevention of peroxidation of membrane lipids (Kalir et al.,

1984).

Effect of salinity on polyphenol oxidase activity

The sodium chloride salinity enhanced the PPO activity

upto the optimum level of 300 mM in Suaeda maritima and

the data are given in (Fig. 6). Beyond, the optimum level, the

PPO activity reduced gradually. Polyphenol oxidase activity

increased with increasing salinity upto optimum concentration of 300 mM in Suaeda maritima. Increased

polyphenol oxidase activity has been reported in halophytes such

as Aegiceras corniculatum (Manikandan and Venkatesan, 2004).

High polyphenol oxidase activity under stress indicates its

ability to oxidize and to degrade the toxic substances such as

phenolic compounds which are generally reported to be

accumulated during salt stress (Subhashini and Reddy, 1990).

Sharp increase in polyphenol oxidase activity under salinity

stress was associated with enhanced rooting in Excoecaria

agallocha, Cynometra iripa and Heritiera fomes (Basak et al.,

2000).

CONCLUSION In the present investigation, the effect of different

concentration of sodium chloride on organic components,

chlorophyll synthesis and activities of certain key enzymes of

Suaeda maritima has been studied. Suaeda maritima could

survive a wide range of 100-500 mM NaCl concentration.

The upper limit for survival of this species to NaCl salinity

was 500 mM. howere, favorable growth response by the

seedlings was confined to 300 mM NaCl.

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Source of support: Nil; Conflict of interest: None declared