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New Insights into the Nitrogen Form Effect on Photosynthesis and Photorespiration

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New Insights into the Nitrogen Form Effect on Photosynthesis and Photorespiration

    New Insights into the Nitrogen Form Effect

    on Photosynthesis and Photorespiration Pedosphere17r(5):601-610,2007

    ISSN1002?0160/CN32??1315/P

    @2007SoilScienceSocietyofChina

    PublishedbyElsevierLimitedandSciencePress

    PEDOSPHERE

    rwwelseviercom/Iocate/pedosphere

    NewInsightsintotheNitrogenFormEffecton

    PhotosynthesisandPhotorespiration1

    GUOShi.Wei,ZHOUYi,GAOYing.Xu,LIYongandSHENQi-Rong

    CollegeoyResourcesandEnvironmentalSciences,NanjingAgriculturalUniversity,NanjingP10095(chin~)?E-mail

    sguo@njau.edu.cn

    (ReceivedJanuary8,2007;revisedJuly26,2007)

    ABSTRACT

    Underhighlightconditions,ammoniumnutritionhasanegativeeffectonplantgrowth.Thissuggeststhatthead-

    verseeffectsofammoniumnutritiononplantgrowthmayberelatedtocarbongain,photosynthesis,andphotorespiration.

    However,thereisnoconsistentevidenceofaspecificmechanismthatcouldexplaintheplantgrowthreductionunder

    ammoniumsupply.Itisgenerallyacceptedthatduringthelightreaction,asurplusofnicotinamideadeninedinucleotide

    hydrogenphosphate(NADPH)isproduced,whichisnotcompletelyusedduringtheassimilationof002.Nitratereduc-

    tionintheleafrepresentsanadditionalsinkforNADPHthatisnotavailabletoammonium-gro

wnplants.Nitrateand

    emamoniumnutritionmayusedifferentpathwaysforNADPHconsumption.whichLeadstodifferencesinphotosynthesis

    andphotorespiration.Themorphological(.e.,cellsize,mesophyllthickness,andchloroplastvolume)andenzymic(i.e.,

    ribulose-1,5-bisphosphatecarboxylase/oxygenase(Rubisco),phosphoenolpyruvatecarboxylase(PEPOase),andglutamine

    synthetase/glutamatesynthetase(GS/GOGAT))differencesthatdevelopwhenplantsaretreatedwitheithernitrate

    orammoniumnitrogenformsarerelatedtophotosynthesisandphotorespiration.Thedifferencesinphotorespiration

    rateforplantstreatedwithnitrateorammoniumarerelatedtotheconversionofcitrateto2-oxoglutarate(2-OG)and

    photorespiratoryC02refixation.

    KeyWords:ammonium,nitrate,nitrogenform,photorespiration,photosynthesis Citation:Guo,S.W.,Zhou,Y.,Gao,Y.X.,Li,Y.andShen,Q.R.2007.Newinsightsintothenitrogenformeffecton

    photosynthesisandphotorespiration.Pedospherc.17r(5):601-610.

    INTRODUCTION

    Theeffectofnitrogenform(nitrate"ve~8"o,8

    oIdum)onplantgrowthandphotosynthesishas

    beeninvestigatedinnumerousstudies(HuppeandTurpin,1994;Wiesler,1997;Gerend~eta1.,1997).

    Manyplantspeciesshowgrowthdepressionswhenammoniumissuppliedasasolenitrogenform(Iil,

    1994;andTerry,1994;ClaussenandLenz,1999)aspureammoniuinnutritionhasanegative effectontheleafarea,relativegrowthrate,anddrymatteryield(ErrebhiandWilcox1990;Raaband

    Terry,1994).Thisresponsetoammoniumismorepronouncedunderhighhghtconditionsbecauseof

    photoinhibition(MagalhaesandWilcox,1984;Zhueta1.,2000).However,nodifferencesindrymatter

    yieldaxefoundbetweennitrogenformsunderlowlightintensity(Seeleta1.,1993;Zhueta1.,2000).

    Theseresultssuggestthatsomeoftheadverseeffectofammoniumnutritiononplantgrowthisrelated

    tophotosynthesis.

    Incontrasttonitratesupply,onecommonfeatLiraofamlnoniulnsupplyisareductionofleaSex.

    pansion(Leidieta1.,1992;w_alch

    Liueta1.,2000),leadingtoahigherribulose.1,5.bisphosphatecar.

    boxylase/oxygenase(Rubisco)amountandactivity,chlorophyllcontentanddensity,andconsequently

    photosyntheticcapacityonaleafaxeabase(RaabandTerry,1994;Guoeta1.,2002;Guoeta1.,2005).

    'ProjectsupportedbytheNationalBasicResearchProgr~raofChina(No.20050B121101),theNationalNaturalScience

    FoundationofChina(Nos.30400279and30671233)andtheInternationalFoundationforScience(IFS)(No.C/3799-1).

    Correspondingauthor.E-mail:shenqirong~njau.edu.cn.

602S.W.GUoetZ.

    However.thesedifferencesvanishifphotosyntheticactivityiscalculatedbasedontheamountofchloro-

    phyll(Guoeta1.,2002;Guoeta1.,2005),indicatingthatthebiophysicalfunctionofthephotosynthetic

    electrontransportchainisunaffected.Thus,itisnotsurprisingthatHegh

    JensenandSchjoerring(1997)

    describedahigherCO2assimilationrateunderammoniumsupply.Atthesametime,higherstomatal

    conductanceandintercellularCO2concentration(asindicatedbycarbonisotopediscrimination)were

    foundforammonium

    suppliedwheatplants.Thisresultsuggeststhecleareffectofnitrogenformon1eaf gasexchangeparameters(i.e.,CO2assimilationrate,intercellularCO2partialpressure,andstomatal

    conductance).htrthermore,CO2assimilationratesona1eafareabasearesignificantlyhigherunder

    ammoniumcomparedtonitratesupplyinsugarbeet(RaabandTerry,1994),Frenchbean(Guoeta1.,

    2005),andhighbushblueberry(ClaussenandLenz,1999),whereasinclover(Hcgh

    JensenandSchjo-

    erring,1997),raspberry,andstrawberry(ClaussenandLenz,1999),nosignificantdifferencesinCO2

    assimilationratesamongNfo.rmsarefound.Suchinconsistentresultsmayindicatedifierencesinthe

    concentrationofNsuppliedrangingfrom0.2to7.5mmolLN(RaabandTerry,1994),ontogeneticor

    seasonaleffectsonrelevantbiochemicalormorphologicaltraits,orspeciestolerancetosoleammonium

    supply(ClaussenandLenz,1999).Inthisarticle,theeffectofnitrogenformontheprocessesrelated

    tophotosynthesisandphotorespirationisreviewed.

    H0WD0NITREANDAMM0NIUMINFLUENCEPH0T0SYNTHESIS?

    PhOtoenergyconsumptionandreductantsupply

    ThedifI-erencesinphoto-energyconsumptionandreductantsupplybetweennitrate

    andammonium

    grownplantshavebeentheoreticallydiscussedinseveralreviewsfRaven,1985;Gerendaseta1.,1997).

    Itisgenerallyacceptedthatthediscrepanciesobservedarerelatedtothedifferentassimilatory

pathways

    ofnitrateandammonium(Fig.1).Briefly,thenitratetakenupbyrootsistransportedintoshoots,and

    thenreducedandassimilatedinthemesophyllcellsofleaf.Nitrateisthenreducedintonitritebynitrate

    reductase(NR)inthecytosol,andnitriteisfurtherreducedtoammoniumbynitritereductasefNiR1in

    thechloroplast.Finally,theammoniumassimilationintoglutamatebyglutaminesynthetase/glutamate

    synthetase(GS/GOGAT)OCCurS.Thereductionof1mo1nitratetoammoniuminilluminatedgreen

    cellscosts16photons(Raven,1985)andthusrepresentsasinkforelectrons(Gerend~seta1.,1997).The

    tota1costinN0absorption,transport,reduction,andassimilationisalmost32mo1photonsmolN

    (Raven,1985).

    ComparedtophotosyntheticC02assimilation,theNassimilationintoglutamateisaveryimpor

    tantsinkforredoxequivalentsfromthephotosyntheticelectronflow(ChampignyandFoyer,1992).

    Therefore,nitrogenassimilationmayregulatesimultaneousCO2assimilation.Whennitrogenisassimi

    1atedquantitativelyintheroot,ammoniumgrownplantssaveabout7.

    6%11.9%oftheoveral1costfor

    growthascomparedtonitrate-grownplants;fortheassimilationintheshootthedifferenceisreduced

    to3.0%-6.1%becauseofthedirectuseofphotons(Gerend~seta1.,1997).Sometimesammoniumis

    toxictoplantsanditstoxiceffectisreducedbyassimilatingtheammoniumintoorganiccompounds

    intherootsviatheglutaminesynthetase/glutamatesynthetase(GS/GOGAT).Theassimilationof

    ammoniuinintherootcausesahighdemandofcarbonskeletonsthatoriginatefromtheTCArtri

    carboxylicacid)cycleintheshoot.Assimilatednitrogenistransportedinthexylemtotheshootin

    theformofaminoacidsandamides(Marschner,1995).Ithasbeensuggestedthatwhe-nammonium

    lssuppliedtoplants,ascomparedtonitrate,thiswouldsavephoto-energy,thatis,10ATPfadenosine

    triphosphate)molN(Salsaceta1.,1987).TotalcostforNH+absorption,transport,reduction,and

    assimilationisalmost9.45mo1photonmolNassimilatedandtransported(Raven,1985).During

    thelightreaction,asurplusofnicotinamideadeninedinucleotidehydrogenphosphatefNADPH)isalso

    produced,whichisnotcompletelyconsumedduringtheassimilationofCO2.Nitratereductionin1eaves

    representsaNADPHsinkinadditiontothatmentionedintheparagraphabove.TllissinkforNADPH

    consumptionisnotavailabletoplantssuppliedwithaininoniuin(Fig.2).AsshownbySalsacetat

NEFFECToNPHOTOSYNTHESISANDPHoToRESPIRATIoN603

    (1987),Bloometa1.(1989),andHuppeandl"ktrpin(1994),nitrogenformsaffecttheconsumptionof

    NADPH,and,becauseofthereductionofNO3inleaf,asubstantialportionofproductsoftheelectron

    transportchaincanbeusedforNO3assimilation.Thephoto-energycostforammoniumsupplyis45%

    lessthanthatfornitratesupply(Raven,1985). L

    Leaf

    noacidS

    RO0t

    noacidS

    NADHFdATP

    NO3NONH.GIutamiRe

    GIutamate

    Fig.2Primaryreactionintheassimilation doxin,ATP--adenosinetriphosphate. DHA

    P

    Chloroplast

    ofNO3?NADHnicotinamideadeninedinucleotide ,Fdredreducedferre-

    

    

    

    

    

    

    _l_

6O4S.W.GUoetf.

    LeafNO3assimilationintoaminoacidsislinkedtotheconsumptionofcarbonskeletonsandp

    ho-

    tosyntheticallygeneratedATPandreductants(NADPH).AlthoughthestoichiometryofATP

    and

    NADPHproductionduringphotosyntheticlightreactionsisnotclearandismostlikelyflexibl

e,the

    rateofATPproductionisgenerallyassumedtobelowerthanthatofNADPHproduction.OneATP

    producedcoststhreephotonsandoneNADPHproducedcoststwophotons,whereasitcosts3ATPand

    2NADPHtofixoneC02.ThesurplusofNADPHiseitherexportedfromthechloroplastsfNoctorand

    Foyer,1998;Guoeta1.,2005)orconsumedeitherduringleafNO3assimilationorbyalternativeelec-

    tronsinks(e.9.,Mehlerreaction).Estimationsofelectronconsumptionbynitrogenassimilationrelative

    tototalconsumption(includingcarboxylationandoxygenation)undernaturalatmosphericconditions

    rangefrom5%to25%(Lewiseta1.,2000;NoctorandFoyer,1998).Thisreductantsinkisprimarily

    causedbyNO3-reductionandassimilation.Furthermore,theprovisionof2

    oxoglutarate(2-OG1re-

    quiredfortheoperationofGOGATmayproduceATPduringmitochondrialrespirationfNoctorand

    Foyer,1998).ComparedtotheseprocessesinNO3

    assimilatingleaves,plantsundersoleNH+supply

    mustreleasetheappropriateamountofCfromleavestorootstoassimilateNH+andtocontrolnet

    NH+uptake(BrittoandKronzucker,2001).Theconsumptionofphotosyntheticallyproducedelectrons

    duringleafNassimilationcomparedtoplantswithrootNassimilationincreasesthetheoreticalquan-

    tumrequirement(NoctorandFoyer,1998).

    ThesefundamentaldifferencesinenergyrequirementsforNassimilationbetweenNo

andNH+

    suppliedplantsshouldhaveconsequencesofleafcarbohydratemetabolismandATP/NADPHbalance.

    wllichareexpectedtoaffectthenetCO2assimilationasfollows.Thestrongcouplingbetweenleaf

    Nmetabolismandphotosynthesisisindicatedbythepositivecorrelationof,forexample.glutamine

    synthesis(Novitskayaeta1.,2002),andthemalateshuttlebetweenthecytosolandstromafStittet0f..

    2002).ThisresultsindifferencesinnetCO2uptakeandO2evolutioninNoandNH+

    suppliedplants

    (Bloometa1.,1989).Furthermore,CO2releasedfrom(photo)respiratoryisrefixedinthecytosol,as

    illustratedbySchweizerandErismann(1985),whofoundthattheactivityofphosphoenolpyruvatecar

    boxylase(PEPCase)washigherintheleafofwheatplantunderNO3supplycomparedtoNH+supply.

    TmshigherPEPCaseactivityshouldaffectthecytosolicCO2concentrationandmitochondrialactivitv

    becauseofitsrefixationofCO2releasedfromeitherphotorespirationorrespirationfKandlbinderet0f..

    1997).Consequently,theCO2compensationpointisregulatednotonlybyPEPcaseactivity(Hlusler

    eta1.,1999),butalsobythereactionofOAA(oxalacetate)withpyruvate,andCO2evolutioninthe

    reactioncitrateto2-OG(seeFig.4inGuoeta1.,2005;NoctorandFoyer,1998),whichreflectsthere-

    lativephotorespirationrate.TheapparentCO2compensationpointresultsinthenecessityofassuming

fight

    dependentchangesinnon-photorespiratoryCO2evolution,whereasthetrueCO2compensation

    pointincludesonlyCO2evolutionfromphotorespiration(Guoeta1.,20051. Ribulosebisphosphateregeneration,ribulose一』,

    5-bisphosphatecarboxylaseactivity,andcarbonintee

    diates

    Undersaturatedfightintensity,CO2assimilationrateislimitedbytheamountandactivityofRu

    biscoatlowintercellularCO2partialpressure(ci),andthecapacitytoregenerateribulosebiphosphate

    (RuBP)athighCi(FarquherandyonCaemmerer,1982;LongandBernacchi.2003).TheRuBP

    regenerationrateisconsideredtobelimitedbyATPsupply,whichisdependenteitherontheelectron

    transportrateortheavailabilityoforthophosphate(Pi)florphotophosphorylation(Sharkey,1985a,

    b).Orthophosphateavailabilityoverashorttimeisdeterminedbythecapacityofstarchandsucrose

    synthesis,toregeneratePifromphosphorylatedphotosyntheticintermediates.Asnitrate-grownplants

    consumemoreNADPHandATP(seeabove),itissuggestedthatthenitrate-grownplantssufferthe

    limitationofphotosynthesisratefromRuBPregeneration(RaabandTerry,1994).Anotherlimiting

    factorofphotosynthesisrateistheribulose-1,5

    bisphosphatecarboxylase(RuBPCase)activitythatis

    regulatedtomaintainabalancebetweenthecapacitiesofthephotosyntheticapparatustoproduceand

    consumeRuBPandtriosephosphates(Sage,1988).Undersaturatedlightintensity,theactiva

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