Biological lett. 2013, 50(2): 63–76available online at: http:/www.degruyter.com/view/j/biolet DOI: 10.2478/biolet-2013-0008

Alleviation of nickel toxicity in wheat (Triticum aestivum L.) seedlings by selenium supplementation

ewAgAjewSkA1,dAnieLdroBik1,mArzenAwieLAnek1, joAnnASekuLSkA-nALewAjko2,jAroSłAwgocłAwSki2,jAnuSzmAzur3

andmAriASkłodowSkA1

1departmentofPlantPhysiologyandBiochemistry,facultyofBiologyandenvironmentalProtection,universityofłódź,Banacha12/16,90-237łódź,Poland

2instituteofAppliedcomputerScience,łódźuniversityofTechnology,Stefanowskiego18/22, 90-924łódź,Poland

3LaboratoryofcomputerandAnalyticalTechniques,facultyofBiologyandenvironmentalProtection,universityofłódź,Banacha12/16,90-237łódź,Poland

correspondingauthor:ewagajewska,ewagaj@biol.uni.lodz.pl

(Received on 28 February 2013; Accepted on 18 September 2013)

Abstract: hydroponicallygrownwheat seedlingswere treatedwith50µmniand/or15µmSe.Af-tera7-daycultureperiod, theirgrowthparameters,ni,Se,fe,andmgcontents,electrolyte leakage,photosyntheticpigmentconcentrations,andphotochemicalactivityofphotosystemiiweredetermined.exposureofwheatseedlingstonialoneresultedinreductioninthetotalshootandrootlengths,by22%and50%,respectively.AdditionofSetotheni-containingmediumsignificantlyimprovedthegrowthoftheseorgans,comparedtotheseedlingssubjectedtonialone.ApplicationofSedecreasedtheaccumula-tionofniinshootsandrootsandpartiallyalleviatedtheni-induceddecreaseinfeandmgconcentationsinshoots.electrolyteleakageincreasedinresponsetonistress,butinshootsitwasdiminishedbySesupplementation.exposuretoniledtoadecreaseinchlorophylla and b contents and enhancement of chlorophyll a/bratio,butdidnotinfluencetheconcentrationofcarotenoids.enrichmentoftheni-con-tainingmediumwithSesignificantlyincreasedchlorophyllbcontent,comparedtotheseedlingstreatedwithnialone.Photochemicalactivity,estimatedintermsofthemaximumquantumyieldofphotosystemii,decreasedinresponsetonitreatmentbutwassignificantlyimprovedbysimultaneousadditionofSe.resultsofourstudysuggestthatalleviationofnitoxicityinwheatseedlingsbySesupplementationmayberelatedtolimitationofniuptake.

Keywords: chlorophyll,electrolyteleakage,nickelstress,photochemicalactivity,selenium

inTroducTion

nickel(ni)isclassifiedasamicronutrientandinsmallquantitiesisessentialfor plant growth (Marschner 1995).however,itsexcessistoxictomostplantspe-cies,which is evidencedbygrowth reduction andoccurrenceofother symptoms,

e.gajewskaetal.64

suchasleafchlorosisandnecrosis.ourearlierstudyindicatedthatniphytotoxic-itymaybeatleastpartlyattributedtoitsabilitytoinduceoxidativestress(Gajew-ska & skłodowska 2007) and disturbance of nitrogenmetabolism (Gajewska & skłodowska2009).Thisheavymetalhasalsobeenreportedtointerferewithmineralnutrition (Pandey & sharma 2002; ouzounidouetal.2006),waterrelations(Pandey & sharMa2002),respiration(LLamas & sanz2008),andphotosynthesis(sheoran et al. 1990; drążkiewicz & Baszyński2010).negativeeffectsofnionphysiologicalandmetabolic processesmay result in decreased biomass production and, conse-quently,considerablyreducedyieldsofcropplants.

Selenium (Se), althoughnot considered tobeanessentialnutrient forplants,at lowdoseshasbeenshown topromote theirgrowth.ThebeneficialeffectofSeonplantsisusuallyascribedtoitsabilitytoenhanceantioxidativecapacityoftheircells (Xueetal.2001; hasanuzzamanetal.2012).ThereisalsosomeevidencethatSemayincreasethetoleranceofplantstovariousabioticstressfactors,suchasuvradiation (Pennanenetal.2002),salinity(kongetal.2005),andheavymetals(FiLek et al. 2008).nevertheless, at highconcentrations thismetalloid is toxic toplants.Thisisrelatedtothecompetitionbetweenseleniumandsulphur,leadingtosynthesisofselenocysteineandselenomethionine,andsubsequentproductionofproteinswithdisturbed function and structure (hasanuzzamanetal.2010).

TheaimofourstudywastoinvestigatetheabilityofSetoalleviatenistressinwheat seedlings. Our study was focused on the effect of Ni and Se used separately andincombinationongrowthparameters,membranepermeability,photosyntheticpigmentconcentrations,andphotochemicalactivityofphotosystemii(PSii).Sincechlorophyllcontentand,therefore,photosyntheticprocessdependontheavailabilityofmgandfeinplanttissues,wealsomeasuredconcentrationsoftheseelements.

mATeriALAndmeThodS

Plant material and growth conditionswheat(Triticum aestivumL.,cv.zyta)seedsweregerminatedinthedarkat24oc

for2days.nexttheseedlingsweretransferredintodiluted(1:4)hoaglandnutrientsolutioncontaining50µmni(niSo4)and15µmSe(na2SeO3) supplied individually orsimultaneously.Theseconcentrationswerechosenonthebasisofthepreliminaryexperiment,showingthatSeatthedoseof15µm(butnotlower)isabletoamelioratewheatseedlinggrowthaffectedby50µmni,thedosethatweusedinourearlierstud-ies (gajewska & skłodowska 2009; gajewskaetal.2012).Theseedlingsgrowninthe nutrient solution without addition of Ni and Se were considered as the control. All theseedlingsweregrowninagrowthroomat24ocwith16-hphotoperiod(photosyn-theticphotonfluxdensity175µmolm-2 s-1).Aftera7-daycultureperiod,thegrowthparameters,concentrationsofni,Se,fe,mg,andphotosyntheticpigments,electrolyteleakageaswellasphotochemicalactivityofPSiiwereestimated.

Growth parametersgrowthparameterswereestimatedbyanautomaticanalysisofscannedimages

of shoots and roots.The imageswereacquiredas jPegfilesbyusinga standard

SeLeniumALLeviATeSnickeLSTreSSinwheAT 65

flatbedscanner.Theshootsandrootswerescannedseparatelyat300dpiand600dpiresolutions,respectively,usinghighlysaturatedbluebackground.Suchbackgroundfacilitatesdistinguishingofplantparts,assumingthatnobluecolourcanbeobservedintheplanttissue.Thescannedimageswereprocesseddigitally,usingspecializedsoftware developed for this purpose in cooperation with the institute ofAppliedcomputerScience,łódźuniversityofTechnology,Poland.ThesoftwareincludesmATLABscriptscallingappropriatelibraryfunctionsofimageanalysis(The MaTh-works inc.2011a) implementedasc++meXfiles (The maThworks inc.2011b).mathematicaldescriptionandvalidationtestsoftheappliedcomputermeasurementmethods for wheat shoot and root systems were published previously (gocławski et al.2009;sekuLska-naLewajko & gocławski2011).Thetotalshootlength,lengthsof the 1standthe2nd leaves as well as the total root length and lengths of primary and secondary roots were determined.

Analysis of elements and estimation of electrolyte leakagefor determination of element concentrations, samples of shoots and roots

(150mgdw each)werewet-digested in amixture (5:1, v/v) of 70%hno3 and 30%h2O2,usingamicrowavemineralizer.concentrationsofni,fe,andmgweredeterminedbyatomicabsorptionspectrometry(SpectrAA300,varian).PriortoSeanalysis,Se6+ present in the samples was reduced to Se4+ by boiling the mineralizates withadditionof6mhclfor1.5h.SeleniumwasdeterminedusingthemethodofwaTkinson(1966)basedonmeasurementoffluorescenceofcyclohexane-extractedselenite-2,3-diaminonaphthalene complex at 370.0nm (excitation) and 520.0nm(emission).electrolyte leakagefromshootandrootcellswasevaluatedconducto-metrically as described earlier (Gajewska et al. 2012).

Photosynthetic pigment concentrations and photochemical activity of PS II fordeterminationofphotosyntheticpigmentconcentrations,the1st leaves were

homogenized twicewith80%acetoneandcentrifuged(33000×g,15min).Aftermeasurementofabsorbanceofthesupernatantsat663.2nm,and470.0nm,chloro-phyll a,chlorophyllb,andtotalcarotenoidcontentswerecalculatedaccordingtothemethod of weLLBurn(1994).

Photochemical activity of PSiiwas estimated by a chlorophyll fluorescence-baseddeterminationofthemaximumquantumyieldofPSii(equivalenttoFv/Fm) byusingaportablefluorometerfluorPenfP100(PhotonSystemsinstruments).Pri-ortomeasurementstheseedlingsweredark-adaptedfor20min.measurementsweredone on the 1stleaf,about1cmbelowitstip.

Statistical analysis The results presented are means of 3 independent experiments. for growth

parameters andquantumyield estimation, 10 seedlingswereusedper experiment(n = 30).fordeterminationofelectrolyteleakageandphotosyntheticpigmentcon-tent,4plantswereusedperexperiment(n = 12).forestimationofelementcontents,a single pooled sample prepared from 20 seedlingswas analysed per experiment(n = 3).Samplevariabilityisexpressedasthestandarddeviation(Sd)ofthemean.

e.gajewskaetal.66

Thesignificanceofchangesbetweenmeanvaluesforeachtreatmentandthecontrolaswellasbetweenmeanvaluesforniandni+Se treatmentsweredeterminedbyStudent’s t-test. Differences at P < 0.05wereconsideredsignificant.

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fig.1.effectofniandSetreatmentsontotalshootlength,lengthsofthe1stand2nd leaves (a) as well as the total root length and lengths of primary and lateral roots (b) of wheat seedlings. Data are means±Sd;**,***significantlydifferentfromthecontrolatP < 0.01 and P < 0.001,respective-ly;^^,^^^significantlydifferentfromnitreatmentatP < 0.01 and P < 0.001,respectively

SeLeniumALLeviATeSnickeLSTreSSinwheAT 67

reSuLTS

exposureofwheatseedlingstoniresultedin22%reductioninthetotalshootlength(fig.1a).Asimilardecreaseinlengthwasalsofoundforthe1stand2nd leaves. comparedtotheabovegroundpartoftheseedling,rootgrowthwasmoreaffectedbynistress.Thetotalrootlengthaswellaslengthsofprimaryandlateralrootsweredecreasedafternitreatmentbyabout50%,comparedtothecontrol(fig.1b).Treat-mentofthewheatseedlingswithSealonedidnotinfluencesignificantlytheshootgrowthparameters,butledtoa16%reductioninthetotalrootlength,comparedtothecontrol(fig.1a-b).Primaryandlateralrootsdifferedin theirsensitivity toSe.Thelengthofprimaryrootswasnotaffected,whilethatoflateralrootswasabout40%lowerthaninthecontrol(fig.1b).

comparedtotheseedlingssubjectedtonialone,thosetreatedsimultaneouslywith Ni and Se showed an improvement of the total shoot length and lengths of the 1stand2ndleaves,byabout25%.intheseedlingstreatedwiththecombinationofniandSe,shootgrowthparametersdidnotdifferfromthoseofthecontrol.AdditionofSe to the Ni-containing medium resulted also in increased total root length as well aslengthsof theprimaryandlateralroots(by67%,81%,and41%,respectively),comparedtotheseedlingssubjectedtonialone(fig.1a-b).

Ni treatment of the seedlings led to considerable accumulation of this metal in thetissues(Table1).mostofni(almost94%ofthetotalamounttakenupbytheseedlings)wasaccumulatedintheroot.ApplicationofSeledtoabout5-foldhigheraccumulationofthiselementintheroots,comparedtotheshoots.intheseedlingstreatedsimultaneouslywithniandSe,niconcentrationinshootsandrootswas33%and45%lower,respectively,thanintheseedlingsexposedtonialone,whileSeup-takebytheseedlingswasnotaffectedbynistress.

Table1.effectofniandSetreatmentsontheiraccumulationinshootsandrootsofwheatseed-lings.dataaremeans±Sd;***significantlydifferentfromthecontrolatP < 0.001;^^^signifi-cantly different from Ni treatment at P < 0.001

Treatmentnicontent[µgg-1dw] Secontent[µgg-1dw]

Shoots roots Shoots roots

control 2.75±0.79 2.84±0.66 0.89±0.20 0.87±0.15

Ni 82.10±5.4***

1239.75±160.09***

0.95±0.16 0.89±0.22

Se 3.04±0.43 2.57±0.25 102.57±6.12***

489.43±39.79***

ni+Se 55.74±2.29***,^^^

677.67±118.04***,^^^

89.84±2.9***

497.51±25.39***

e.gajewskaetal.68

exposuretoniresultedinenhancementofelectrolyteleakagefromshootandrootcells,asitwas122%and19%higher,respectively,thaninthecontrol(fig.2).Seappliedindividuallydidnotinfluenceelectrolyteleakage,neitherintheshootsnorintheroots.however,additionofSetotheni-containingmediumsignificantlyre-ducedelectrolyteleakagefromshootcells,ascomparedtotheseedlingstreatedwithnialone.incontrast,suchaprotectiveeffectofSewasnotfoundintheroots.

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fig.2.effectofniandSetreatmentsonelectrolyteleakagefromwheatshootandrootcells.dataaremeans±Sd;*,***significantlydifferent fromthecontrolatP < 0.05andP < 0.001,respectively;^^^significantlydifferentfromnitreatmentatP < 0.001

SeLeniumALLeviATeSnickeLSTreSSinwheAT 69

Applicationofniledtodecreaseinfeandmgconcentrationsinthewheatshoots,by33%and20%, respectively (fig.3a-b). in comparison to the seedlings treatedwithnialone,inthosesubjectedtobothSeandnitheconcentrationoffewas23%higher,butstillremainedbelowthecontrolvalue(fig.3a).concentrationofmginthe shoots of the seedlings grown in the presence of Ni and Se applied simultaneously didnotdiffersignificantly fromthecontrol (fig.3b).whensupplied individually,

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fig.3.effectofniandSetreatmentsonfe(a)andmg(b)contentofwheatshoots.dataaremeans±Sd;*,**significantlydifferentfromthecontrolatP < 0.05andP < 0.01,respec-tively;^significantlydifferentfromnitreatmentatP < 0.05

e.gajewskaetal.70

Sedidnotinfluencefeandmgconcentrationsinwheatshoots.inourexperiment,feconcentrationintherootswasnotaffectedbyniandSetreatments.mgconcentra-tionintherootsofni-exposedseedlingsdecreasedby43%,comparedtothecontrol,and was not improved by Se supplementation (data not shown).

exposuretoniresultedindecreasedchlorophylla and chlorophyll b concen-trations in the 1stleaves,by15%and26%,respectively,ascomparedtothecontrol(fig.4a).Amorepronounceddecreaseinchlorophyllb than in chlorophyll a content wasreflectedbytheincreasedvalueofchlorophylla/bratio,whichintheseedlingstreatedwithniwas14%higherthaninthecontrol(fig.4b).Seappliedindividuallydidnotinfluencechlorophyllconcentrationinleaves,butitsadditiontotheni-con-tainingmediumsignificantlyenhancedtheconcentrationofthispigment,whichwasaccompanied by considerable reduction of total chlorotic area on the leaves (data not

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fig.4.effectofniandSetreatmentsonchlorophyllcontent(a),chlorophylla/bratio(b),caroteno-idcontent(c),andmaximumquantumyieldofphotosystemii(d)inwheatleaves.dataaremeans±Sd;**,***significantlydifferentfromthecontrolatP < 0.01 and P < 0.001,respectively;̂ ,̂ ^^significantlydifferentfromnitreatmentatP < 0.05andP < 0.001,respectively

SeLeniumALLeviATeSnickeLSTreSSinwheAT 71

shown).intheseedlingsgrowninthepresenceofniandSe,chlorophylla content didnotdifferfromthatinthecontrol,whilechlorophyllb content was increased by 14%,ascomparedtotheseedlingstreatedwithnialone(fig.4a).nevertheless,com-paredtothecontrol,chlorophyllbconcentrationintheleavesofseedlingsexposedtothecombinationofniandSewasstillsignificantlylower,andchlorophylla/b ratio exceededthecontrolvalueby10%(fig.4a-b).Thetotalcarotenoidconcentrationinwheatleaveswasnotaffectedbyni(fig.4c).

intheleavesofni-treatedwheatseedlings,themaximumquantumyieldofPSiiwassignificantlyreduced,by16%incomparisontothecontrol(fig.4d).enrichmentoftheni-contaminatedmediumwithSeincreasedquantumyieldby17%,comparedto the seedlings treated with Ni alone.

diScuSSion

growth inhibition is regarded as themost common symptomofheavymetalstressinplants.Theheavy-metal-inducedgrowthreductionhasbeensuggestedtore-sult from restriction of cell division and cell elongation (cho & Park2000)aswellasfrom metabolic disturbances (gajewska & skłodowska2009).consistentlywithpre-viousreportsconcerningnitoxicityinplants(Pandey & sharma2002;ouzounidou etal.2006),weobservedinthewheattreatedwith50µmniconsiderabledecreasesinshootandrootlengths,withrootsshowinggreatersensitivitytonistresscomparedto aboveground parts of the tested seedlings. Addition of Se to the Ni-containing me-diumsignificantlyimprovedthegrowthofwheatseedlings,whichwasevidencedbyincreasesintotalrootandshootlengths.inagreementwithourresults,ameliorationof growth due to Se supplementation was also found in Ni-treated lettuce seedlings (hawryLaketal.2007).Similarly,Se-inducedgrowthpromotionhasbeenreportedforplantssubjectedtocdstress(FiLeketal.2008;ZemBaLa etal.2010).Apartfromprotection against heavymetals, Se has also been shown to counteract the stressinduced in plants by other abiotic factors. Published data suggest that the ability of Se to neutralize various environmental stresses can be ascribed to several different mechanisms,buttheyhavenotbeenfullyelucidatedyet(FenGetal.2013).

inourstudy,Seappliedindividuallydidnotinfluenceshootgrowthbutreducedthe lengthof lateralroots.SinceourpreliminaryexperimentrevealedthatSedos-eslowerthan15µmwereinsufficienttoalleviatethereductionofwheatseedlinggrowthcausedby50µmni,inthepresentexperimentwedecidedtouseSeattheconcentrationof15µm,despiteitsslightinhibitoryeffectonrootgrowth.

exposuretoniresultedinasignificant increaseinniconcentrationinwheatseedlings,mainlyintheroots.greateraccumulationofniinroottissuesmayexplainstrongergrowthinhibitionof thisorgan,comparedto theshoot.ApplicationofSeconsiderablyreducedtheaccumulationofni,bothinshootsandinrootsofthewheatseedlings.incontrast,inni-stressedlettuce,supplementationwithSeincreasedniaccumulation in the leaves (hawryLaketal.2007).Similarlytoourwork,Se-evokedreductioninmetaluptakehasbeenreportedforplantstreatedwithcr,cd,andPb(shanker et al. 1996; srivasTavaetal.1998;heetal.2004;FiLeketal.2008).Limi-tationofheavymetaluptakebySemayberelatedtotheformationofnon-toxicSe-

e.gajewskaetal.72

metalcomplexes,whichconsiderablyreducestheavailabilityofthemetaltoplants(shankeretal.1996).ThecounteractingeffectofSeonheavymetaluptakehasalsobeenexplainedbycompetitionofthemetalandSeionsforthebindingsitesintheprotein carriers (kumaretal.2012).

membranepermeability,estimatedintermsofelectrolyteleakagefromcells,hasbeenreportedtoincreaseinplantssubjectedtoheavymetals,includingni(LLaMas et al.2008;PoPovaetal.2009).Similarly,intheni-treatedwheatseedlings,wefoundenhancedelectrolyteleakagefromshootsandroots.ourearlierstudysuggestedthatthe destructive effect of Ni on membranes might be associated with increased lipid peroxidationaswellaschangesinfattyacidprofile,resultingindecreasedlipidun-saturation (Gajewska etal.2012).inaddition,findingsofouzounidouetal.(2006)indicated that membrane structure and functioning might also be affected due to dis-placementofca2+ from the membrane ligands by Ni2+ions.ourexperimentrevealedthat supplementation of the ni-containing medium with Se significantly reducedelectrolyteleakagefromshootcells.AsimilarameliorativeeffectofSeonmembranepermeability was observed in the shoots of As-treated mungbean (maLik etal.2012).results obtainedbykumar et al. (2012) implied that improvement of the heavy-metal-disturbed membrane function by Se might be associated with enhancement offattyacidunsaturation.wesuggestthatSe-inducedprotectionofcellmembranesunderconditionsofnistressisrelatedmainlytoaugmentationofantioxidativeca-pacity. Such a supposition is in agreement with the results of studies documenting decreasesinlipidperoxidationandreactiveoxygenspeciesaccumulationaswellasincreasesinantioxidativeenzymeactivitiesandnon-enzymaticantioxidantcontentsafter supplementation of heavy-metal-stressed plants with Se (Pedreroetal.2008;hasanuzzamanetal.2012;kumaretal.2012).

disturbeduptakeofessentialelementsisconsideredtobeoneofthemainrea-sons of heavymetal toxicity in plants. in accordancewith earlier studies dealingwith the effect of Ni on mineral composition of plant tissues (Pandey & sharma 2002;ouzounidouetal.2006),intheshootsofni-treatedwheatseedlingswefounddecreasedfeandmgcontents.impaireduptakeofpolyvalentcationsduetonihasbeensuggestedtoresultfromtheircompetitionforspecificbindingsitesintheroots (ouzounidouetal.2006).ApplicationofSesignificantlycounterbalancedtheni-in-duceddecreaseinfeandmgconcentrationsinwheatshoots,whichmightberelatedtothegeneralbeneficialeffectofSeonmembranes.Toourknowledge,theamelio-rative effect of Se on concentrations of these elements in Ni-stressed plants has not been reported so far. zemBaLa etal.(2010)intheshootsofcd-treatedwheatfoundaslightSe-inducedenhancementoffecontent,buttheydidnotobserveanyimprove-mentinmgcontent.

reducedchlorophyllconcentrationand theresultant leafchlorosishaveoftenbeenobservedinplantssubjectedtonistress (Fargašovǎ 1998; ouzounidou et al. 2006).inlinewiththosereports,intheleavesofni-treatedwheatseedlingswefoundasignificantdecreaseinbothchlorophylla and chlorophyll b contents. Our results indicatethatadeclineinchlorophyllcontentmightbeatleastpartlyduetoni-evokeddeficiencyofmg(astructuralcomponentofthispigment)andoffe,whichpartici-pates in its biosynthesis (Marsh et al. 1963). A deleterious effect of Ni on chlorophyll

SeLeniumALLeviATeSnickeLSTreSSinwheAT 73

concentration has also been suggested to be a consequence of the metal-induced in-hibition of enzyme activities involved in its synthesis and stimulation of chlorophyl-lase activity (aBdeL-BasseTetal.1995;szymańska & maTraszek 2005).ourstudyrevealed a higher sensitivity of chlorophyll btonistress,incomparisontochloro-phyll a,whichwasconsistentwiththefindingsofFargašovǎ (1998) in white mus-tard.incontrast,hawryLaketal.(2007)inleavesofni-treatedlettuceobservedagreater reduction of chlorophyll a than of chlorophyll bcontent.resultsobtainedbydrążkiewicz and Baszyński (2010)suggestedthattheeffectofnionchlorophylla/b ratiomightdependonthetimeofexposure.Similarlytoourstudy,inmaizetreatedwithnifor8daysthoseauthorsnoticedanincreaseinchlorophylla/bratio,butafter13daysitsvaluedecreased.incontrasttothefindingofhawryLaketal.(2007),whoreportedamarkedreduction in the totalcarotenoidconcentration in lettuce leavestreatedwith50µmni,wedidnotobserveintheni-exposedwheatanydecreaseinconcentration of these pigments.

ApplicationofSepositivelyinfluencedchlorophyllconcentrationinleavesofni-treatedwheat,sothatintheseedlingsexposedtothecombinationofniandSe,chlorophyll a concentration did not differ from that in the control.chlorophyllb content,althoughsignificantlyincreasedincomparisontotheni-treatedseedlings,was still lower than in the control. Partial alleviation of Ni-induced decline in chloro-phyll content by Se application may be related to its protective effect on chloroplast enzymesinvolvedinchlorophyllbiosynthesis,mostlyduetoantioxidantpropertiesof Se (Pennanen etal.2002).

inagreementwithpreviousstudies(drążkiewicz & Baszyński2010;veLikova etal.2011),themaximumquantumyieldofPSiiinwheatleaveswassignificantlyreducedinresponsetoniexposure.Adeclineinthisparameterhasbeensuggestedtobeassociatedwith the limited reoxidationofplastoquinoneAbyadecreaseorpartialblockingofelectrontransportfromPSiitoPSi(veLikova etal.2011).earlierreports provided evidence that the negative effect of Ni on photosynthesis is multidi-rectional.inadditiontodisturbanceofphotochemicalreactionsandreductioninpho-tosyntheticpigmentcontents,decreasesintheactivitiesofthecalvincycleenzymes(sheoran et al. 1990) and changes in chloroplast ultrastructure (moLas1997;FiLek etal.2010)wereobserved.inthepresentstudywedemonstratedthattheapplicationofSesignificantlyincreasedquantumyieldintheleavesofni-treatedwheatseed-lings.ourresultsimplythatimprovementofphotochemicalactivityofPSiibySesupplementationmightbeatleastpartlyrelatedtothebeneficialeffectofthiselementon chlorophyll concentration and integrity of chloroplast membranes. Literature data indicate that Se may also counterbalance the detrimental impact of heavy metals onphotosynthesisbyincreasingunsaturationandfluidityofchloroplastenvelopeaswell as by amelioration of chloroplast size and ultrastructure (FiLek etal.2010).

concLuSionS

ourstudyshowsthatSeapplicationsignificantlyalleviatestoxiceffectsinducedbyniinwheatseedlings,whichwasevidencedbyimprovedgrowth,increasedfe,mg,andchlorophyllconcentrations inshoots,enhancedphotochemicalactivityof

e.gajewskaetal.74

PSii,andreducedelectrolyteleakagefromshootcells.TheresultssuggestthatthebeneficialeffectofSemaybeassociatedwithlimitationofniuptakebytheseed-lings.furtherstudiesareneededtogetbetterinsightintothemechanismsofallevia-tionofnitoxicitybySe.

Acknowledgements:Thisworkwassupportedbytheuniversityofłódź(grantno.506/819).

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