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Journal of Plant Physiology 164 (2007) 685—694

0176-1617/$ - sdoi:10.1016/j.

Abbreviationacid; WUE, wa�Correspond

fax.: +92 41920E-mail addr

www.elsevier.de/jplph

Does exogenous application of salicylic acidthrough the rooting medium modulate growth andphotosynthetic capacity in two differently adaptedspring wheat cultivars under salt stress?

Muhammad Arfana, Habib R. Atharb, Muhammad Ashrafa,�

aDepartment of Botany, University of Agriculture, Faisalabad, PakistanbDepartment of Botany, Institute of Pure and Applied Biology, Bahauddin Zakariya University, Multan, Pakistan

Received 7 March 2006; accepted 10 May 2006

KEYWORDSCarotenoids;Hydroponics;Photosynthesis;Photosyntheticpigments;Salinity stress;Yield

ee front matter & 2006jplph.2006.05.010

s: A, net CO2 assimilatter use efficiency.ing author. M. Ashraf, D0312.ess: ashrafbot@yahoo.c

SummaryIn order to assess whether exogenous application of salicylic acid (SA) through therooting medium could modulate the photosynthetic capacity of two wheat cultivarsdiffering in salinity tolerance, a hydroponic experiment was conducted undergreenhouse conditions. Seeds of a salt tolerant (S-24) and a moderately salt sensitive(MH-97) cultivar were germinated at 0 or 150mM NaCl in Hoagland’s nutrientsolution containing different levels of salicylic acid (SA) (0, 0.25, 0.50, 0.75 and1.00mM) for 7 d. Seven-day old wheat seedlings were transferred to hydroponics andgrown at 0, or 150mM NaCl for for further 30 d. Different levels of salicylic acid (SA)were also maintained in the solution culture. After 30 d, four plants out of six wereharvested and the remaining plants were left for the estimation of yield attributesSalt stress reduced the growth and grain yield of both cultivars. However, cv. S-24performed better than MH-97 under salt stress with respect to leaf area, and grainyield. Exogenous application of SA promoted growth and yield, and counteracted thesalt stress-induced growth inhibition of salt tolerant S-24, whereas for MH-97 therewas no improvement in growth or grain yield with SA application. Of the varying SAlevels used, the most effective levels for promoting growth and grain yield were 0.75and 0.25mM under normal and saline conditions, respectively. The improvement ingrowth and grain yield of S-24 due to SA application was associated with improvedphotosynthetic capacity. Changes in photosynthetic rate due to SA application were

Elsevier GmbH. All rights reserved.

ion rate; Ci, sub-stomatal CO2; E, transpiration rate; gs, stomatal conductance; SA, salicylcic

epartment of Botany, University of Agriculture, Faisalabad, Pakistan. Tel and

om (M. Ashraf).

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not due to stomatal limitations, but were associated with metabolic factors, otherthan photosynthetic pigments and leaf carotenoids.& 2006 Elsevier GmbH. All rights reserved.

Introduction

Salt stress can affect physiological processesfrom seed germination to plant development,resulting in reduced growth and yield (Ashraf,2004). The complexity of the plant responses tosalt stress can be partially explained by the factthat salinity imposes both ionic and osmotic stressas well as nutritional imbalance (Ashraf, 2004).Photosynthesis is a key metabolic pathway inplants. Maintaining good photosynthetic rate leadsto maintenance of growth under salt stress. Thedecline in net photosynthesis under salt stresscould be due to stomatal or non-stomatal limita-tions, or both (Dubey, 2005).

Photosynthesis plays an important role in plantproductivity. While working with modern andobsolete cotton cultivars, Faver et al. (1997)suggested that improvements in cotton yield maybe achieved through enhanced assimilatory pro-cesses in modern cultivars. Similarly, Shuting et al.(1997) found that the maize cultivars with highergrain yield maintained higher rates of photosynth-esis than low yielding cultivars during plant devel-opment. Stomatal conductance, transpiration rate,leaf area and length of grain filling period were allhigher in high yielding cultivars. In asparagus,Faville et al. (1999) found that rate of photosynth-esis had a positive association with the crop yield.Thus, final biological or economic yield can beincreased by increasing the rate of photosynthesis.Therefore, increasing the efficiency of photosynth-esis has long been a goal of plant research (Natr andLawlor, 2005).

The site of the photosynthesis in plants ispredominantly the green leaf and its productivitydirectly depends upon the chlorophyll bearing sur-face area, irradiance and its potential to utilize CO2

(Hirose et al., 1997). Leaves are the majorcontributors to net productivity during vegetativeand reproductive growth stages. The leaf photosyn-thetic activity becomes crucially important whenthe fruit is a harvestable yield (Hansen, 1969).

Salicylic acid is a common plant-produced phe-nolic compound that can function as a plant growthregulator (Arberg, 1981). Although various physio-logical and biochemical functions of SA in plantshave been reported (Raskin, 1992); exogenousapplication of SA may also influence a range of

developmental and physiological processes, e.g.,seed germination and fruit yield (Cutt and Klessing,1992), transpiration rate (Larque-Saavedra, 1979),stomatal closure (Rai et al., 1986), membranepermeability (Barkosky and Einhellig, 1993),growth and photosynthesis (El-Tayeb, 2005; Khanet al., 2003; Khodary, 2004). SA also has receivedmuch attention due to its role in plant responses toabiotic stresses such as ozone (Koch et al., 2000),UV-B (Surplus et al., 1998), heat stress (Clark et al.,2004; Dat et al., 1998, 2000) drought (Nemeth etal., 2002; Senaratna et al., 2000; Singh and Usha,2003), oxidative stress (Shim et al., 2003), salt andosmotic stress (Borsani et al., 2001; El-Tayeb, 2005;Khodary, 2004).

In view of all afore-mentioned reports, thepresent study was conducted to assess whetherexogenous application of SA through the rootingmedium could alleviate the adverse effects of saltstress on wheat cultivars differing in salinitytolerance. The present study also aimed to examinewhether SA-induced changes in photosyntheticcapacity could modulate growth and grain yield oftwo differently adapted wheat cultivars.

Materials and methods

Seed of a salt tolerant (S-24) and a moderatelysalt sensitive cultivar (MH-97) of spring wheat wereobtained from the Department of Botany, Univer-sity of Agriculture, Faisalabad, Pakistan and AyubAgricultural Research Institute, Faisalabad, Paki-stan, respectively. A hydroponic experiment wasconducted during the winter of 2004–2005 in a net-house at the Botanic Garden of the University ofAgriculture, Faisalabad, Pakistan (latitude 311300N,longitude 731100E and altitude 213m), with 10/14light/dark period at 800–1100 mmolm�2 s�1 PPFD, aday/night temperature cycle of 26/15 1C and6575% relative humidity. The seed of both culti-vars were surface sterilized with 5% sodium hypo-chlorite for 5min and then thoroughly rinsed withdistilled water before further experimentation.Seed (100 seeds of each cultivar; 25 seeds perPetri plate) of both cultivars were allowed togerminate on filter paper moistened with half-strength Hoagland’s nutrient solution and salicylicacid (0.00, 0.25, 0.50, 0.75 and 1.00mM in Petri

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plates) under non-saline (0mM NaCl) or salineconditions (150mM NaCl) for 7 d. Seven-day oldwheat seedlings of both cultivars were thentransferred in plastic containers (45� 66� 23 cm)containing 20 L of half strength Hoagland’s nutrientsolution supplemented with or without salicylicacid (0.00, 0.25, 0.50, 0.75 and 1.00mM in therooting medium) under non-saline (0mM NaCl) orsaline conditions (150mM NaCl). The treatmentswere organized following a completely randomized(CRD) with four replicates (six seedlings perreplicate of each cultivar). The nutrient solutionwas replaced weekly. All treatment solutions werecontinuously aerated. After 30 d, the followingphysiological attributes were measured.

Chlorophyll contents

Chlorophyll ‘a’ and ‘b’ contents were deter-mined according to the method of Arnon (1949).Fresh leaves (0.2 g) were cut and extracted over-night with 80% acetone at 0–4 1C. The extracts werecentrifuged at 10,000� g for 5min. Absorbance ofthe supernatant was read at 645, 663 and 480 nmusing a spectrophotometer (Hitachi-U2001, Tokyo,Japan).

Chlorophyll fluorescence

The polyphasic rise of fluorescence transientswas measured by a plant Efficiency Analyzer (PEA,Handsatech Instruments Ltd., King’s Lynn, UK)according to Strasser et al. (1995). The transientswere induced by red light at 3000 mmolm�2 s�1

provided by an array of six light emitting diodes(peak 650 nm), which were focused on the samplesurface to give homogenous illumination over theexposed area of sample surface. All the sampleswere dark adapted for 30min prior to fluorescencemeasurements.

Gas exchange parameters

Measurements of gas exchange attributes weremade on second intact leaf from the top of eachplant using an ADC LCA-4 portable infrared gasanalyzer (Analytical Development, Hoddesdon,UK). These measurements were made from 10:30to 12:30 h with the following specifications/adjustments: leaf surface area, 11.25 cm2; watervapor pressure into the chamber ranged from6.0 to 8.9mbar, ambient CO2 concentration,352 mmolmol�1; temperature of the leaf chambervaried from 28.4 to 32.4 1C; leaf chamber gas flowrate (U), 251 mmol s�1; molar flow of air per unit

leaf area (Us) 221.06molm�2 s�1; RH of thechamber 41.2%; PAR (Qleaf) at the leaf surface atnoon was up to 918 mmolm�2 s�1; ambient pressurewas 98.8 kPa.

After 30 d, four plants out of six were harvestedand the remaining plants were left for the estima-tion of yield attributes such as grain yield per plant,and 100-grain weight. Plant roots were removedfrom the hydroponic system and washed in coldLiNO3 solution isotonic with the correspondingtreatment. Plants were separated into shoots androots and then blotted dry before recording theirfresh masses. All plant parts were dried at 65 1Cuntil constant dry mass, and their dry massesmeasured.

Statistical analysis of data

The data were subjected to analysis of varianceusing a COSTAT computer package (Cohort Soft-ware, Berkeley, CA). The mean values werecompared with the least significance differencetest following Snedecor and Cochran (1980).

Results

Salt stress reduced (Po0.001) the shoot freshand dry mass, and leaf area of both cultivars(Fig. 1). However, root fresh and dry masses, shootand root lengths and number of tillers were notreduced due to salt stress. Application of 0.75mMsalicylic acid (SA) through the rooting mediumincreased (Po0.001) in fresh and dry masses ofboth shoots and roots, shoot length, and leaf areaof cv. S-24 under non-saline conditions, whereasunder saline conditions this was true at 0.25mM SA.However, in MH-97 application of 0.75mM SA alsoincreased fresh and dry masses of both shoots androots under non-saline conditions, but this effectwas very small.

Salt stress caused a reduction (Po0.001) in grainyield per plant, 100-grain weight and number ofspikelets for both cultivars, whereas number ofspikes per plant and number of fertile tillersremained largely unaffected in both cultivars(Fig. 2). Exogenous application of 0.75mM SAimproved the grain yield, number of grains, andnumber of spikelets per spike of cv. S-24 under non-saline conditions. However, 100-grain weight of cv.S-24 was improved by 0.25 and 0.50mM SAapplication through the rooting medium undernon-saline conditions. In contrast, in MH-97 onlynumber of grains was increased, due to 0.75mM SAapplication under non-saline conditions (Fig. 2).

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Figure 1. Fresh and dry weights of shoots and roots, shoot and root length, number of leaves and number of tillers perplant of two wheat cultivars differing in salinity tolerance when plants were grown hydroponically to varyingconcentrations of salicylic acid under saline or non-saline conditions (number of replicates n ¼ 4; vertical lines ingraphs are standard errors).

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However, salt-induced reduction in grain yield, 100-grain weight and number of grains was considerablyameliorated in S-24 due to 0.25mM SA application.In contrast, grain yield of MH-97 was slightlyimproved with 0.50mM SA application under salineconditions (Fig. 2).

Imposition of salt stress reduced (Po0.001) thenet CO2 assimilation rate (A), transpiration rate(E), stomatal conductance (gs), sub-stomatal CO2

(Ci), and water use efficiency (WUE ¼ A/E) of both

cultivars, but did not alter Ci of S-24 (Fig. 3).Exogenous application of 0.50 and 0.75mM SAincreased A of S-24 under non-saline conditions,whereas that of non-salinized MH-97 plants wasdecreased by 1.00mM SA. However, under salineconditions, application of 0.25mM SA was found tobe effective in increasing A in S-24 (Fig. 3).Similarly, under saline conditions, the higher con-centrations of SA (0.75 and 1.00mM) increased theA in MH-97.

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Figure 2. Grain yield per plant, 100 grain weight, number of spikes per plant, number of spikelets per spike, number offertile tillers per plant and number of grains per plant of two wheat cultivars differing in salinity tolerance when plantswere grown hydroponically at varying concentrations of salicylic acid under saline or non-saline conditions (number ofreplicates n ¼ 4; vertical lines in graphs are standard errors).

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Transpiration rate and stomatal conductance ofboth cultivars were decreased by SA applicationunder non-saline conditions, whereas under salineconditions the pattern of increase or decrease in gsand E of both cultivars was inconsistent withincrease in SA level (Fig. 3) However, Ci in MH-97was increased due to 0.25, 0.50 or 0.75mM SAapplication under saline conditions. In contrast, Ci

of S-24 was decreased due to SA applicationthrough the rooting medium (Fig. 3). Furthermore,exogenous application of SA improved the WUE ofboth cultivars under saline conditions.

Neither salt stress nor SA application changed thelight reaction efficiency of PSII (Fv/Fm) for eitherwheat cultivar (Fig. 3). However, salt stressreduced (Po0.001) the chlorophyll ‘a’ content of

both cultivars (Fig. 4). Leaf chlorophyll ‘a’ of S-24was increased with 0.25 or 1.00mM SA applicationunder saline conditions, whereas that of MH-97decreased with an increase in SA application underboth non-saline and saline conditions (Fig. 4).However, the pattern of increase or decrease inleaf chlorophyll ‘a’ of S-24 was inconsistent with anincrease in SA application under both non-salineand saline conditions. The chlorophyll ‘a/b ratio’ ofMH-97 remained almost unchanged by salt stress,whereas it decreased in S-24 (Fig. 4). All doses of SAcaused a reduction in chlorophyll ‘a/b ratio’ of MH-97 under both non-saline and saline conditions.In contrast, in S-24, 0.75 and 1.00mM SA applica-tions caused an increase in chlorophyll ‘a/b ratio’under non-saline conditions, whereas under saline

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Figure 3. Net photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs) substomatal CO2 (Ci), A/E andFv/Fm of two wheat cultivars differing in salinity tolerance when plants were grown hydroponically to varyingconcentrations of salicylic acid under saline or non-saline conditions (number of replicates n ¼ 4; vertical lines ingraphs are standard errors).

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conditions only 1.00mM SA application increasedchlorophyll ‘a/b ratio’. Leaf carotenoids of bothcultivars were not changed due to salt stress (Fig. 4).All doses of SA application caused a reduction(Po0.01) in carotenoids of MH-97 under non-salineconditions, whereas under saline conditions only0.25mM SA application reduced carotenoids in MH-97. In contrast, the pattern of increase or decreasewith an increase in SA level was inconsistent in S-24under both saline and non-saline conditions.

Discussion

In the present study, salt stress caused areduction in growth and grain yield in both wheatcultivars. This adverse effect of salt stress was

considerable on photosynthesizing leaves, grainyield and grain weight. In addition, the inhibitoryeffect of salt stress was more pronounced on MH-97than on S-24. This cultivar variation for salinitytolerance was expected, because line S-24 is knownfor high salt tolerance (Ashraf, 2002) and MH-97 ismoderately salt sensitive (Iqbal and Ashraf, 2005).Exogenous application of SA through the rootingmedium had an ameliorative as well as growthpromoting effect under both non-saline and salineconditions. These results can be related to earlierstudies which observed that exogenous applicationof SA promotes growth and counteracts the stress-induced growth inhibition due to abiotic stresses ina range of crop species (Zhou et al., 1999; Tariet al., 2002; Shakirova et al., 2003; Singh andUsha, 2003; Khodary, 2004; El-Tayeb, 2005). Forexample, salinity stress-induced growth inhibition

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Figure 4. Chlorophyll ‘a’ and ‘a/b’ ratio, and carote-noids of two wheat cultivars differing in salinity tolerancewhen plants were grown hydroponically to varyingconcentrations of salicylic acid under saline or non-salineconditions (number of replicates n ¼ 4; vertical lines ingraphs are standard errors).

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was alleviated by exogenous SA application throughthe rooting medium on the growth of tomato (Tariet al., 2002) and Phaseolus vulgaris (Stanton,2004). Similarly, foliar spray with SA also mitigatedthe adverse effects of salt stress on growth ofmaize (Khodary, 2004) or promoted the growth insoybean (Gutierrez-Coronado et al., 1998). Whileworking with wheat, Singh and Usha (2003) re-ported that foliar spray with SA counteractedgrowth inhibition in wheat caused by water stress,one of the major factors caused by salinity stress inplants. Salicylic acid-induced increase in growth ofwheat under non-saline or saline conditions can beattributed to an increase in photosynthesizingtissue, i.e., leaves (Dhaliwal et al., 1997; Zhou

et al., 1999), which is in agreement with ourresults, because a positive relationship was foundbetween A and leaf area (Leaf area vs.Ar ¼ 0.232*).

Growth and grain yield of S-24 were increased bySA applied through the rooting medium and thiseffect was more pronounced at 0.75mM SA undernon-saline conditions, whereas under saline condi-tions the most effective concentrations of SA were0.25 and 0.50mM. Overall, there was no effect ofSA application on growth and yield of cv. MH-97under both non-saline and saline conditions. Fromthese results, it can be concluded that beneficialeffect of SA application depends on type of speciesor cultivar. This is supported by earlier studies. Forexample, Bezrukova et al. (2004) reported that0.05mM SA application through the rooting mediumwas effective in improving growth of wheat.However, the same positive effect of 0.5mM SAwas observed on the growth of barley when addedto the solution culture for 24 h in the presence orabsence of Cd (Metwally et al., 2003). Exogenousapplication of 0.5mM SA for 24 h led to increasedantioxidant capacity of barley plants (Ananievaet al., 2004). In view of these reports, as well asthe data reported here, it is evident that effectiveconcentrations of SA differ from species to species.In addition, the effectiveness of SA dose dependson the plant age at which it is applied.

In the present study, increase in grain yield alongwith increase in 100-grain weight, number of grainsand number of spikelets per spike of cv. S-24 with0.25mM SA application under saline conditions(Fig. 2) suggested that improvement in salt-inducedreduction in grain yield with SA application wasmainly due to increase in grain size and number.This is in agreement with Grieve et al. (1992) whoobserved that reduction in total yield in saltstressed wheat occurs through inhibition of spikeletnumber and spikelet survival, but it varies withgenotype and level of stress. Although actual roleof SA in improving grain yield is not evident, it canbe stated that the beneficial effect of SA on grainyield may have been due to translocation of morephotoassimilates to grains during grain filling,thereby increasing grain weight. These results aresimilar to those of Zhou et al. (1999) who reportedthat maize plants stem injected with SA, produced9% more grain weight than those with sucrose anddistilled water treatments. The second possiblemechanism of SA-induced yield enhancement mightbe an increase in the number of spikelets andnumber of grains, because SA has the capacity toboth directly or indirectly regulate yield. Forexample, flower induction in cocklebur (Clelandand Ajami, 1974) and Spirodela polyrrhiza (Khurana

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and Maheshwari, 1980), photosynthesis in barley(Pancheva et al., 1996), maize (Zhou et al., 1999;Khan et al., 2003), and soybean (Kumar et al.,2000; Khan et al., 2003), and boll number in cotton(Hampton and Oosterhuis, 1990) were found to beup-regulated by SA application. The third possibi-lity is the enhancement in net CO2 assimilation rate(A) of S-24 when 0.75 and 0.25mM SA was appliedunder non-saline and saline conditions, respec-tively. Thus, an improved photosynthetic rate of S-24 due to SA application might have contributedmore to biomass production and grain yield undernon-saline or saline conditions. The results for S-24can be related to earlier findings reported regard-ing improvement in photosynthetic rate due toexogenous SA application which enhanced growthand/or yield in several crops, e.g., barley (Pan-cheva et al., 1996), maize (Khan et al., 2003;Khodary, 2004; Zhou et al., 1999), soybean (Khan etal., 2003; Kumar et al., 2000). Although exogenousapplication of SA improved A in MH-97 under salineconditions, it did not in turn improve growth andyield. A similar cultivar variation for relationshipbetween growth and yield, and photosyntheticcapacity has earlier been observed in hexaploidwheat cultivars (Ashraf and Bashir, 2003), andpotato (Gawronska et al., 1990; Hammes and DeJager, 1990).

Changes in photosynthesis due to exogenous SAapplication under environmental stresses are dueto either stomatal or non-stomatal limitations(Athar and Ashraf, 2005; Brugnoli and Bjorkman,1992; Dubey, 2005). Since SA application canreverse the stomatal closure induced by ABA (Raiet al., 1986), an increase in photosynthetic rate byreversing salt-induced stomatal closure with SAapplication is plausible. However, in the presentstudy, gs was decreased with SA application,particularly under non-saline conditions. The re-duction in gs and E due to SA application can berelated to the findings of Larque-Saavedra (1978)who observed that exogenous SA application had anantitranspirantion effect on the leaves of Phaseolusvulgaris and caused reduction in stomatal conduc-tance in epidermal strips of Commelina communis(Larque-Saavedra, 1979). However, an increase ordecrease in A due to SA application in both cultivarswas not accompanied by an increase or decrease ings and E under both saline and non-saline condi-tions. This is in agreement with some other findingson different crops, e.g., cotton (Constable andRawson, 1980), sunflower (Rawson and Constable,1980), and wheat (Ashraf, 2002; Ashraf and Bashir,2003). Furthermore, increased photosynthetic ratein cv. S-24 along with low sub-stomatal CO2,suggests that S-24 can utilize available CO2 inside

the leaf more effectively at 0.75 and 0.25mM SAapplied under non-saline or saline conditions,respectively. In addition, an increase in A due toSA application with a decrease in gs, along with Ci

suggests that the increase in A is probably due tometabolic factors including photosynthetic pig-ments, carotenoids, efficiency of photosystem II(PSII), rubisco enzyme concentration and activity,supply of ATP and NADPH to photosynthetic carbonreduction cycle and use of assimilation products(Athar and Ashraf, 2005; Lawlor and Cornic, 2002).Of these variables only efficiency of photosystem II(Fv/Fm), photosynthetic pigments and carotenoidswere determined in the present study. However,quantum yield of PSII (Fv/Fm) was not changed dueto salt stress or SA application. Thus, quantum yieldof PSII cannot be considered as one of the factors toregulate A in the two wheat cultivars underinvestigation, which differ in salt tolerance.

In the present study, total carotenoids werereduced by salt stress in both cultivars. However,exogenous application of 0.25 and 1.00mM SAincreased leaf carotenoids in S-24 under salineconditions, whereas in MH-97, total carotenoidsremained almost unchanged due to SA applicationunder saline conditions. It is suggested that SAapplication increased the antioxidant capacity andprotection of the photosynthetic apparatus in S-24.This view is further supported by the fact that S-24had a higher chlorophyll ‘a’ concentration and/orchlorophyll a/b ratio when 0.25mM SA was appliedunder saline conditions. This effect of SA applica-tion on photosynthetic pigments was expected inview of earlier studies that showed increased ordecreased photosynthetic pigments following SAapplication, depending on type of species orcultivar. For instance, Chandra and Bhatt (1998)observed that an increasing or decreasing effect ofSA on chlorophyll content of cowpea (Vignaunguiculata) depends on the genotype. In anotherstudy, treatment with SA increased pigment con-tents in soybean (Zhao et al., 1995), maize (Sinhaet al., 1993; Khodary, 2004), and wheat (Singh andUsha, 2003) grown under normal or stress condi-tions. However, in the present study, parallelscannot be drawn between rate of photosynthesisand chlorophyll ‘a’ level, or chlorophyll a/b ratio.Thus, changes in photosynthetic pigments mightnot have been responsible for the increase inphotosynthetic rate but might have been due toother metabolic factors such as Rubisco and PEPcarboxylase (Pancheva et al., 1996). Although theactivity of rubisco was not determined in thepresent study, it is possible that SA-inducedincrease in rubisco activity was responsible forincrease in photosynthetic rate, as has earlier been

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observed in wheat genotypes (Gomez et al., 1993;Rajasekaran and Blake, 1999; Singh and Usha, 2003)when grown under normal or stress conditions.

From the above discussion, it can be concludedthat salt-induced reduction in growth and grainyield in wheat can be improved by the exogenousapplication of SA, which is true for salt tolerant cv.S-24. This improvement in growth and grain yield ofS-24 due to SA application was associated withimproved photosynthetic capacity. Changes inphotosynthetic rate due to SA application weredue to metabolic factors, other than photosyn-thetic pigments and leaf carotenoids. However, cv.S-24 was higher in growth and photosynthetic tissue(leaf area) than MH-97 under saline conditions,which could explain the ability of the salt tolerantS-24 to show better grain yield under salt stressthan the moderately sensitive MH-97. Thus theresponse to exogenous SA application is cultivarspecific.

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