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Difference

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Difference

    Difference

    Pedosphere16(5):646-653,2006

    ISSN1002??0160/CN32??1315/P

    ?2006SoilScienceSocietyofChina

    PublishedbyElsevierLimitedandSciencePress

    DifferenceinSelenium

    ofTwoRiceCultivars1

    PEDOSPHERE

    wwwelseviercorn/locate/pedosphere

    AccumulationinShoots

    ZHANGLian-He,.SHIWei.Ming,andWANGXiao-Chang.

    StateKeyLaboratoryofSoilandSustainableAgriculture,InstituteofSoilScience,ChineseAcademyofSciences

    Nanjing210008(China).E-mail:zlianhe@eyou.CO'~FI,

    AgriculturalCollege,HenanUniversityofScienceandTechnology,Luoyang471003(China)

    .DepartmentofTeaScience,Zh~iangUniversity,Hangzhou310029(China) (ReceivedMarch8,2006;revisedJuly19,2006)

    ABSTRACT

    Twojaponicarice(OryzasativaL.)cultivars,Xiushui48andS.Andrea,differingintheirabilitytoaccumulateSe

    inthegrain(ashighasathree-folddifference),werecomparedforselenium(Se)accumulationintheirshootswhentheir

    growthmediawassuppliedwithdifferentformsofSe.Resultsindicatedthatwhentreatedwith0.25m0lLlNa2SeO3,

    Xiushui48accumulationofSeintheshootswassignificantlymorerapid(P<0.05)thanS.Andrea,probablybecause

    ofgreaterSeuptakeandtransportinXiushui48.Xiushui48riceseedlingshadahighershoot.Seaccumulationrateand

    absorbedselenocysteine(Se-Cys)morerapidlythanS.Andreaseedlings.However,whentreatedwithSeas0.25/~mol

    Lselenomethionine(Se-Met),theS.Andreaseedlings'accumulationratewassignificantlygreater(P0.05)thanthat

    ofXiushui48.Possibly.thehighSeaccumulationrateofXiushui48seedlingshootscomparedtoS.Andreashootswas

    theresultofahighercapacityofXiushui48totransformselenitetoorganicSecompoundsandahigherseleniteuptake

    rate.

    KeyWords:ricecultivars,Seaccumulation,selenite,transport,uptakerate INTR0DUCT10N

    Selenium(Se)isarequiredmicronutrientforanimalsandhumans.Itformsactivesitesinseleno-

    proteinsasselenocysteineandexertsmanyimportantfunctionsinhumanhealth.Seisanantioxidant

    preventingfreeradicals'damagetocells(Stadtman,1980).secanalsoreducetheriskofcertainforms

    ofcancer(Clarketa1.,1996;Combseta1.,1997)andalleviatesomesymptomsofAIDSfHorieta1.,

    1997).SomeSeresponsivediseasesarerelatedtosollSedeficiencyresultingfromSeleachingfromsoils.

    TheinfluenceofSeonpeople'shealthhasbecomeaconcernofglobalenvironmentandhealthrLiet

    a1.,2004).Thus,appropriateintakeofSecanbebeneficialtohumanhealth,especiallyforpopulations

    livinginSe-deficientregionsoftheworld.

    PeopleacquireSemainlyfromtheirdiet,andcerealgrainsareimportantsourcesofSealongwith

    othermicronutrients.Asoneofthecerealgrains,rice(OryzasativaL.)playsacrucialroleinthefood

    supplyofChina(Lieta1.,2005),anditisalsoanefficientwaytosupplementSeinthehumandiet.The

    Secontentinricegrainsofmanycultivars,however.istoolowtoprovideenoughSetomeethuman

    needs.ThoughfoliarspraycouldremarkablyimprovetheSecontentofcerealgrains(Bubereta1.,1995;

    Caoeta1.,2001;Hueta1.,2002),itwasassociatedwithhighcostsandpotentialenvironmentproblems.

    Therefore,manipulatingplantfoodstoaccumulatemoreSecouldbeaninexpensivealternativefIpet

    a1.,1994).WiththeincreaseofenvironmentalawarenessinChina'sagriculturalregionsfAneta1.,2005:

    Heeta1.,2005;Hueta1.,2004;Kongeta1.,2004;Pmelckeeta1.,2004),itwasareasonablestrategvfor

    supplyingSetopeopletoutilizetheSe-enrichmentpotentialofricegraintovastlyincreaseSelevels.

    ProjectsupportedbytheNationalNaturalScienceFoundationofChina(No.40371063)andtheNationalKeyBasic

    ResearchSupportFoundationofChina(No.G1999011808).

    Correspondingauthor.E-mail:wmshi@issas.ac.cn.

SEACCUMULATIONINRICESHooTS647

    AlteringthekeyfactorsthatinfluenceSeaccumulationinthegraincouldaccomplishthis.Ithasbeen

    reportedthattransportofSefromrootstoshoorsplayedanimportantroleinSeaccumulationingrains

    (Zhangeta1.,2003).Therefore,improvingthecapacityofSetransportbyenhancingtheefficiencyof

    transportingmetaboliteswas:likelytoelevateSelevelsinbrownricegrain. Riceplantsabsorbedmostlyselenite.becauseselenatewasreducedtose1eniteunderthesubmerged

    conditionofricepaddies(WangandGao,2001).Oncerootsabsorbedselenite,theycouldrapidlybe

    furthertrans:fc,rmedtoorganicSecompounds(deSouzaeta1..,1998;Gissel-.Nielsen.,1979;Zayedet

    a1.,1998).Selenitewasalsoincorporatedintoglutathione(GsH)formingGS

    Se-SGnon-enzymatically

    (AndersonandScarf..1983;Anderson,1993).Then,NADPHcouldreduceGS

    Se-SGtoGSSeH,and

    theactionofGSHreductasecouldfurtherreduceittoGS-.Se

    (TsangandSchifr,1978)withcysteine

    synthasestillfurtherreducingittoselenocysteine(Se-?Cys)(NgandAnderson,1978). Researchhasshownthat,inplantssuppliedwithselemite,theSecontainingaminoacidswasbiosyn-

    thesizedintherootsbefforebeingtranslocatedtoshoots(Gissel-.N[ielsen.,1979).DeSouzaeta1.f1998)

    reportedthatselenomethioninefSe-Met)wastheprimaryorganicf0rmofSeinroots.TheSeshoot:root

    ratiowasreportedtobelessthan0.5whensuppliedwithseleniteand0.6

    1.0whensuppliedwithSe-Met

    (Zayedeta1.,1998),indicatingthatthebiosynthetictransformationsofinorganicSespeciesinroots

    couldgreatlyaffectthetranslocationefficiencyofSetoshootswhenselenitewassuppliedinthegrowth

    reedia.

    TheaimsofthisstudyweretocompareSeaccumulationinshootsoftworiceseedlingcultivars,

    Xiushui48andS.AndreadifferingintheirSeaccumulationefficiency,whenselenitewassup

pliedin

    thenutrientmedia;andtoinvestigatethedifferenceinSeuptakeinducedbySemetabolites,suchas

    Se-CysorSe-Met,inordertounderstandthekeyfactorsdeterminingSeaccumulationinshoots.

    MATERIALSANDMETH0DS

    Riceseedlingscre

    Twojaponicarice(OryzasativaL.)cultivars,Xiushui48andS.Andrea,wereculturedhydroponi-.

    callyingrowthchambersunderadiurnalcycleof14hat24.Cfordaytimeand10hat18.Cfor night.Humiditywas67'%,andthelightintensityattheplanttopswasapproximately300pmdm.

    s_.photosyntheticphotonflux.AJftertheseedsgerminatedfortwodays.theywereculturedinquarter-

    strengthKimuraBnutrielntsolutions(CSPP..1985)andchangedtofuall-strengthnutrientsolutionsafter

    threedays.Then,the10-.doldriceseedlingswithsimilarsizewerechosenandculturedseparatelYin

    5Lpotscontaining0.25#molLNa2SeO3.SeCysorSe

    Met.Thenutrientsolutionswererefreshed

    atintervalsoffourdaysandthePHwasadjustedto5.5everydaywith1#molL

    NaOHand1#too1

    L_.HC1.Theshootsandrootsofthericeseedlingswereharvestedaftertheywere12,14,16and18

    daysold.

    Riceseedlings,withoutSetreatmelnt,wereharvestedaftertheywere15-20daysold.Theroots

    wereexcisedatthebaseoftheshootsandthenplacedinto100mLbeakerscontaining100#malL

    ofKH2P04,100InolL_.ofCa(NO3)2,andi00molLI1ofMgCI2(pH5.5)for30min.Thesero

ots

    werethentransl,ferredto100mLbeakerscontaining5mmolLMESf2-fN

    morpholino)ethanesulfonic

    acid),0.5mmolL_.Ca(NO3)2,andeither0.06#toolL_.SeCysorSe

    Metseparately,.,todetermine

    theuptakeofSefr,"omthetwoSesourcesovera3hperiod.Therootswerethenrinsedfor15minin

    ice-coldsolutionscontaining5mmolLI1MEs,0.5mmolL-1Ca(NO3)2,andK2804toremovethe

    adsorbedSeontherootsurfacesfAbedineta1.,2002).

    Determination

    Alltheglassvesselsusedwerepreviouslysoakedin10%HC1toeliminateSecontamination.Root

    andshootsamples(dryweight)wereweighedandputinto100mLdigestiontubes.Next,a5mLacid

    mixtureofHNO3andHC104(4:1,v/v)wasadded,andthesamplesweredigestedat25.Covernight.

648L.H.ZHANGenZ.

    Sampleswerethencompletelydigestedat150-165.Cinadigestionovenuntilthesolutionbecame

    clear.Aftercoohng,a2.5mLaliquotof6mo1LHC1wasaddedtoreduceSeO:toSeO4

    andthe

    digestswereheatedto100.C.Heatingcontinueduntilgaseousbrownfumesceasedandthesolution

    becameclear(MurphyandCashman,2001;Zhangeta1.,2003).Aftercooling,thedigestedsamples

    weredilutedto25mLwithdoubledistilled,deionizedwater.Seconcentrationsinthedigestedsamples

weredeterminedbyatomicfluorescencespectrometry(BRAICAF

    610A,Beijing,1999),followingthe

    methoddevelopedbyGmiz

    GraciaandLuquedeCastrof1999).A11thereagentsusedintheanalysis

    weresuperpureguaranteegrade.Astandardmaterialoftea(GSV

    4,0.072mgSekg,GBW07605)

    andablankweresimultaneouslydigestedwiththetestsamples,withanaverageSerecoverybetween

    89%and93%.

    Dataanalysis

    Using0.25#molL-1Na2SeO3,Seaccumulationratesintheshootsofthetworicecultivarswere

    comparedwithSeshoot:rootratiosbeingdeterminedwhentheywere12,14,16and18daysold.Then,

    using0.25mo1LSe-CysorSe

    Met,Seaccumulationratesintherootsandshootsofthetworice

    cultivarsandSeshoot:rootratioswerecompared.Additionally,excisedrootsfrom15daysweretested

    with0.06#molL

    Se-CysorSe-MettodeterminetheSeabsorptionrateofthetworicecultivars. 11datainthetablesandfiguresweresubjectedtoone-wayANOthatwereperformedtocompare

    thedifferencesbetweenXiushui48andS.AndreausingSPSS11.5forMicrosoftWindows. RESUI,S

    SeaccumulationratesinshootsofthetworicegenotypessuppliedwithNoaSeO3 Fig.1displaysthedifferencesinSeaccumulationrateswhentreatedwith0.25#molL

    Na2SeO3

    forseedlingshootsofthetwogenotypesstudied.ForeachmeasurementdaytheSeaccumulationrateof

    Xiushui48wassignificantlygreater(P=0.05)thanS.Andrea.Thus,thecapacityofSeaccumu

lation

    inshootsofXiushui48wasclearlygreaterthanthatofS.Andrea.Also,datashowedthattheSe contentinbrownricegrainswaspositivelycorrelatedwiththetota1Seinshoots(Zhangeta1.,2006b).

    Inaddition,Iab1eIpresentsthecalculatedSeshoot:rootratiosforXiushui48andS.Andrea.showing

    thatXiushui48wassignificantlymoreeffective(P=0.05)thanS.AndreaintransportingSefromroots

    toshoots

    2.5

    2O

    1.5

    

    1.0

    E

    0.5

    0.O

    12141618

    Time(days)

    Fig?1DifferencesinSeaccumulationratesoftheshootsofthetworicegenotypessuppliedwith0.

    25molL-1Na2SeO3

    intheirgrowthmedia.Barsmarkedbythesameletter(s)arenotsignificantlydifferentatP=O.05.Errorbarsindicate

    standarddeviations=3).

    SeaccumulationratesinshootsofXiushui8andS.AndreasuppliedwitheitherSe

    CysorSe.Met

    Fig.2ashowsthedifferenceinshootSeaccumulationratesforthetworicecultivarsstudiedwhen

    treatedwith0.25#molLSeasSeCyswiththeSeaccumulationrateofXiushui48beingsignificantly

    ?.Icol1?一丁I_亡丁oo??

SEACCUMULATIONINRICESHooTS

    TABLEI

    649

    RatiosofshootSetorootSeinXiushui48andS.Andreariceseedlingssuppliedwith0.25/~molLNa2Se03(Means

    SD,n=3)

    SignificantlydifferentfromXiushui48atP<0.05

    ,

    'a

    

    E

    10

    8

    6

    4

    2

    0

    12141618

    30

    20

    10

    0

    Time(days)

    12141618

    Fig2DifferencesinSeaccumulationratesoftheshootsofthetworicegenotypessuppliedwith

0.25/zmolL1Seas

    selenocysteine(a)andselenomethionine(b)intheirgrowthmedia.Barsmarkedbythesameletter(s)arenotsignificantly

    differentatP=O.05,Errorbarsindicatestandarddeviations(n=3).

    higherfP<0.051thanS.Andrea.However,theshootSeaccumulationrateforS.Andreawassignifi.

    cantlyhigher(P0.05)comparedtoXiushui48whensuppliedwith0.25#molL_.Se

    Met(Fig.2b).

    TheseresultssuggestedthatthechemicalformoftheSetypesuppliedaffectedSeaccumulationrates

    intheshootsofXiushui48andS.Andrea.Furthermore,theSeaccumulationratesinthetworice

    genotypestreatedwithSe

    Met(Fig.2b)wassignificantlygreater(P0.05)thanthosetreatedwith

    Se

    Cys(Fig.2a).Hence,SetransportfromrootstoshootsforseedlingstreatedwithSe.Metwasmuch

    moreefficientthanthatwithSeCys.

    SeaccumulationratesinrootsofXiushui48andS.AndreasuppliedwitheitherSeCysorSe

    Met

    When0.25#molL

    lSe.Cyswassupplied.SeaccumulationratesintherootsofS.Andreawere significantlyhigher(P<0.05)thanthoseintherootsofXiushui48(Fig.3a).Similarly,therootsofS,

    Andreahadsignificantlyhigher(P<0.051SeaccumulationratescomparedtoXiushui48rootswhen

    treatedwith0.25pmolL_.Se

    Met(Fig.3b).TheseresultssuggestedthatS.Andrearootshadahigher

    SeaccumulationratethanXiushui48rootsregardlessoftheformofSesupplied(i.e.Se

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