27Improvingplantabioticstressresistancebyexogenous

DROUGHTSTRESSImprovingDroughtTolerancebyExogenousApplicationofGlycinebetaineandSalicylicAcidinSunflowerM.Hussain1,M.A.Malik1,M.Farooq1,M.Y.Ashraf2&M.A.Cheema11DepartmentofAgronomy,UniversityofAgriculture,Faisalabad,Pakistan2NuclearInstituteforAgricultureandBiology,Faisalabad,PakistanIntroductionManyenvironmentalfactorsincludingtemperatureextremes,droughtandsalinityplayverysignificantrolesinreducingagriculturalproductionworldwide(Boyer1982).Inthefaceofaglobalscarcityofwaterresources,droughthasalreadybecomeaprimaryfactorinlimitingcropproductionworldwide.Atpresent,around18%oftheglobalfarmlandisirrigated(morethan240millionhectares)andupto40%oftheglobalfoodsupplyisproducedonthisland(SomervilleandBriscoe2001).Itisthusimperativetoimprovethedroughttoleranceofcrops.Acommonadverseeffectofwaterstressoncropplantsisthereductioninfreshanddrybiomasspro-duction(AshrafandO’Leary1996)andreducedbio-massproductionresultingfromwaterstresshasbeenobservedinalmostallgenotypesofsunflower(TahirandMehdi2001).Whenplantsareexposedtoabioticstresses,plantcellsprotectthemselvesfromthestressofhighconcentrationsofintracellularsaltsbyaccumulat-ingavarietyofsmallorganicmetabolitesthatarereferredtocollectivelyascompatiblesolutes(AshrafandFollad2007).Compatiblesolutesaresmallmole-culesthatareverysolubleinwaterandarealsouni-formlyneutralwithrespecttotheperturbationofcellularfunctions,evenwhenpresentathighconcentra-tions(Yanceyetal.1982).Thepropertiesofthesesolutesallowthemaintenanceofturgorpressureduringwaterstress,whichisanintrinsicfeatureofmajorformsofabioticstresssuchasdrought,saltandcoldstress(SakamotoandMurata2002).Keywordsexogenousapplication;glycinebetaine;salicylicacid;drought;sunflower;proline;yieldCorrespondenceDrM.Farooq,DepartmentofAgronomy,UniversityofAgriculture,Faisalabad38040,PakistanTel.:[phone]/2936Fax:[phone]Email:[e-mail]17,2008doi:10.1111/j.1439-037X.2008.00305.xAbstractWatershortageisaseverethreattothesustainabilityofcropproduction.Exog-enousapplicationofglycinebetaine(GB)andsalicylicacid(SA)hasbeenfoundveryeffectiveinreducingtheadverseaffectsofdroughtstress.ThisstudywasconductedtoexaminethepossibleroleofexogenousGBandSAapplicationinimprovingtheyieldofhybridsunflower(HelianthusannuusL.)underdifferentirrigationregimes.Therewerethreelevelsofirrigation,viz.control(normalirrigations),waterstressatvegetativestage(irrigationmissingatvegetativestage)andwaterstressatfloweringstage(irrigationmissingatfloweringstage).GBandSAwereappliedexogenouslyat100and0.724mm,respectively,eachatthevegetativeandatthefloweringstage.ControlplantsdidnotreceiveapplicationofGBandSA.Waterstressreducedtheheaddiameter,numberofachene,1000-acheneweight,acheneyieldandoilyield.Nevertheless,exogenousGBandSAapplicationsignificantlyimprovedtheseattributesunderwaterstress.However,droughtstressincreasedthefreeleafprolineandGB,andwerefurtherincreasedbyexogenousapplicationofGBandSA.However,exogenousGBapplicationatthefloweringstagewasmoreeffectivethanothertreatments.Oilcontentswerealsoreducedunderwaterstress;however,GBandSAappli-cationcouldnotamelioratethenegativeeffectofwaterstressonacheneoilcontents.TheeffectsofwaterstressandfoliarapplicationofGBweremorepronouncedwhenappliedatthefloweringstagethanatthevegetativestage.J.Agronomy&CropScience(2008)ISSN0931-2250ª2008TheAuthorsJournalcompilationª2008BlackwellVerlag,194(2008)193–199193Manystrategiesarebeingpractisedintheworldtocopewithwaterscarcity;exogenousapplicationofcom-patiblesolutesistheonethatisgettingconsiderableattentioninpresent-dayagriculturalresearch(Azametal.2005,Iqbaletal.2005,AshrafandFollad2007).Thesesolutesincludesugarpolyols,aminoacids,prolineandglycinebetaine(N,N,N-trimethylglycine,GB),etc.(Ludlowetal.1985).GBisanaminoacidderivativethatissynthesizedbyalargenumberoforganismsincludingmembersoftheplantfamiliesChenopodiaceae,Amaranthaceae,Gramineae,CompositaeandMalvaceae(RhodesandHanson1993,Blundenetal.1999,McNeilletal.1999).Inadditiontoitsfunctioninosmoregulation,GBhasbeenshowntoprotectfunctionalproteins,enzymes(e.g.Rubisco),andlipidsofthephotosyntheticapparatusandtomaintainelectronflowthroughthylakoidmembranes(XingandRajashekar1999,Allakh-verdievetal.2003).Furthermore,evenitshighconcen-trationdoesnotexertadverseeffectsonproteinstructure,enzymeactivities,membranefunctionsandmetabolicprocessesoccurringwithinthecell(RhodesandHanson1993,Farooqetal.2008a).Iqbaletal.(2005)reportedthatfoliarapplicationof100mmGBatvegetativestageismorebeneficialinalleviatingtheeffectsofwaterstressandimproving100-acheneweightandthusincreasingacheneyieldofsunflower.Salicylicacid(SA)isanendogenousgrowthregulatorofphenolicnature,whichparticipatesintheregulationofphysiologicalprocessesinplants,anditisalsoimportantindiseaseresistance(Raskin1992).Itplaysanimportantroleinabioticstresstoleranceandconsid-erableattentionhasbeenfocusedontheabilityofSAtoinduceprotectiveeffectonplantsunderstress(Farooqetal.2008b).ManystudiesreporttheroleofSAininducingstresstoleranceinplants(Datetal.1998a,FletcherandHofstra1988,Senaratnaet