免费文献传递   相关文献

Cd2+ induced changes of ascorbate-glutathione cycle in Cd sensitive rice mutant cadB-1 leaves

Cd2+诱导的镉敏感水稻突变体cadB-1叶片抗坏血酸循环的变化



全 文 :植物营养与肥料学报 2015,21(2):346-353 doi牶1011674/zwyf.20150208
JournalofPlantNutritionandFertilizer htp://www.plantnutrifert.org
收稿日期:2014-08-18   接受日期:2015-01-22
基金项目:菏泽学院博士基金项目(XY13BS01)资助。
作者简介:沈国明(1975—),男,浙江绍兴人,博士,讲师,主要从事植物逆境分子生理和农产品安全生产研究。Email:gmshen@tzc.edu.cn
Cd2+诱导的镉敏感水稻突变体 cadB1叶片
抗坏血酸循环的变化
沈国明
(菏泽学院植物生物学重点实验室,菏泽学院生命科学系,山东菏泽274015)
摘要:【目的】镉离子 (Cd2+)为非必需的微量元素,植物易从土壤中吸收并积累Cd2+,通过食物链进入人体内,对
人类的健康造成重大威胁。为了阐明Cd2+诱导氧化胁制和抑制生长的机制,对 Cd2+敏感水稻突变体 (cadB1)进
行了水培试验。【方法】植物材料为水稻粳稻中花11(OryzasativaL.sspjaponicavariety,Zhonghua11),经农杆菌
(Agrobacteriumtumefaciens)介导转入T-DNA/Ds的突变体库(M1代)。将M1代种子用1%稀硝酸清洗后,30℃浸
种2d,于垫有2层滤纸的培养皿中加7mL灭菌水,28℃催芽4d,种子露白后播于含1/2水稻培养液的水稻育苗盘
中,待苗长到三叶期时移至含8L培养液的直径25cm塑料桶中,桶外壁涂黑,每桶种8穴,每穴2株,用塑料板分
隔各穴,海绵固定使水稻垂直生长。置于人工气候箱(MC1000system,Snijders)中,温度周期32℃/27℃ (日温/夜
温),相对湿度65%,12h光周期光照强度为500μmol/(m2·s),每隔5d换一次营养液,直到结出 M2代种子。
将中花11野生型与M2代突变体种子用以上同样方法培养,长到五叶期。以不加 Cd2+作为对照,分别加入01、
025、05和075mmol/LCd2+进行筛选,每种处理平行培养3桶,作为重复,共6001桶,每天定时观察。12d后,
发现05mmol/LCd2+中的中花11野生型没有死亡,而M2代突变体出现部分死亡。按所在位置,选取表型最明显
的株系命名为cadB1。取cadB1种子按上述方法萌发,然后均匀发芽的幼苗与上述相同条件培养,至七叶期,水稻
幼苗包括野生型 (WT)和 cadB1用 05mmol/LCdCl2处理2、4、6、8和 12d。【结果】1)叶片中 Cd和过氧化氢
(H2O2)积累量cadB1高于野生型;2)叶片中还原型谷胱甘肽(GSH)和氧化型谷胱甘肽、抗坏血酸和脱氢抗坏血
酸及还原型烟酰胺腺嘌呤二核苷酸磷酸和氧型烟酰胺腺嘌呤二核苷酸磷酸的比值都是 cadB1低于野生型;3)叶
片中抗坏血酸氧化酶 (ascorbateperoxidase,APX,EC111111),还原型谷胱甘肽酶(glutathionereductase,GR,
EC1642),脱氢抗坏血酸还原酶(dehydroascorbatereductase,DHAR,EC1851)和单脱氢抗坏血酸还原酶
(monodehydroascorbatereductase,MDHAR,EC1654)活性都是cadB1低于野生型。【结论】cadB1具有低水平
的抗氧化剂和抗氧化酶活性。此外,cadB1比 WT积累更多的 Cd从而产生更多的活性氧 (reactiveoxygenspecies,
ROS)。也就是说,与野生型相比,cadB1更缺乏防御力来清除更多的活性氧,从而导致较低的生长势和对 Cd的
敏感。
关键词:抗坏血酸-谷胱甘肽循环;镉敏感突变体;生长抑制;过氧化氢;水稻
中图分类号:S51101   文献标识码:A   文章编号:1008-505X(2015)02-0346-08
Cd2+inducedchangesofascorbateglutathionecycle
inCdsensitivericemutantcadB1leaves
SHENGuoming
(KeyLaboratoryofPlantBiology/DepartmentofLifeSciences,HezeUniversity,Heze,Shandong274015,China)
Abstract:【Objectives】Cd2+iseasilyabsorbedfromthesoilbyplantsandaccumulationinplantswhichhealth
threattohumansthroughhumanfoodchain.Toinvestigatethemechanismofcadmium(Cd2+)inducedoxidative
stressandinhibitgrowthinaCdsensitivericemutant(cadB1),ahydroponicexperimentwasconducted.
【Methods】Ajaponicarice(Oryzasativa)varietyZhonghua11andthemutantriceseedlingsobtainedfromthe
samericevarietyasthatformerlyconstructedwithTDNA/DsinsertionmediatedbyAgrobacterium.The
2期    沈国明,等:Cd2+诱导的镉敏感水稻突变体cadB1叶片抗坏血酸循环的变化
transgeneticricegenerationshavestablehereditabilityandwereusedinthisexperiment.Theseedsweresurface
sterilizedin05% sodiumhypochloritefor20min,rinsed,andgerminatedinthedarkonmoistenedfilterpaperat
30℃ for2d,andthenmovedtoaplasticscreenfloatingondistiledwaterat28℃ for4d.Thenuniformly
germinatedseedlingsweretransferedtoblackpolyethylenebarelswhichcontained6Lofriceculturesolution.
Seedlingsweregrowninagrowthchamberwithaphotofluxdensityof500μmol/(m2·s),relativehumidityof
approximately65% andday/nighttemperaturesof32℃/27℃ (14h/10h).Duringthegrowthperiod,the
solutionwasrenewedevery5d.Atthesevenleafstage,riceseedlingsincludewildtype(WT)andcadB1
exposedto05mmol/LCdCl2for0(ascontrol),2,4,6,8,or12d.【Results】1)Cdandhydrogenperoxide
(H2O2)accumulationwerehigherincadB1thaninwildone;2)Theratiosofreducedglutathione(GSH)and
oxidizedglutathione(GSSG),ascorbate(ASC)anddehydroascorbate(DHA),orreducednicotinamideadenine
dinucleotidephosphate(NADPH)andoxidizednicotinamideadeninedinucleotidephosphate(NADP+)were
lowerincadB1thaninWT;3)Ascorbateperoxidase(APX,EC111111),glutathionereductase(GR,EC
1642),dehydroascorbatereductase(DHAR,EC1851)andmonodehydroascorbatereductase(MDHAR,
EC1654)activitieswerelowerincadB1thaninWTinleavesduringCdCl2exposureperiods.【Conclusion】
cadB1haslowerlevelofantioxidantsaswelasloweractivityofantioxidantenzymes.Inaddition,cadB1
accumulatesmoreCdmeansthatitcanproducemorereactiveoxygenspecies(ROS).Videlicet,cadB1is
deficientofthedefensepoweragainstincreasedlevelofROSwhichleadstoalowergrowthpotentialandsensitiveto
Cd.
Keywords牶ascorbateglutathionecycle牷cadmiumsensitivemutant牷growthinhibit牷hydrogenperoxide牷rice
  Cadmiumcanbereadilytakenupbyrootsand
oftenaccumulatestoalargenumberinplantsystem[1],
thepresenceofCdcaninducethegenerationof
reactiveoxygenspecies(ROS).Plantshavedeveloped
antioxidantmechanismstoaleviatehazardousefects
imposedbyoxidestress.Thesemechanismsinclude
antioxidativeenzymaticandantioxidativenonenzymatic
systems.Theascorbateglutathione(ASCGSH)cycle
isthekeystoneofthenonenzymaticantioxidative
defensesystemandhasbeensuggestedasthesource
forH2O2remova1intoorganeles
[23].ASCandGSH,
twolowmolecularweightantioxidantsareofgreat
importanceinpreservingawiderangeofmetabolic
processes[4].TheycanbothreactdirectlywithROSas
welasparticipatinginROSdetoxificationthroughthe
ASCGSHcycle[2,57].Moreover,ASCandGSHare
alsoassociatedwiththecelularredoxbalanceandthe
ratiosofASC∶DHAandGSH∶GSSGmayfunctionas
signalsfortheregulationofantioxidantmechanisms[8].
Previously,wescreenedaricecadmiumsensitive
and hyperaccumulation mutantby Agrobacterium
tumefacienssystem,investigatedtheenzymaticdefense
system, root morphology and cadmium uptake
kinetics[910].Inpresentresearch,wemainlycompared
thediferencesintheASCGSHmetabolismbetween
cadB1 and WT seedling leavesafterincreasing
exposureperiodsofCd.Althoughrecentlywereported
someresultsofASCGSHmetabolism[1112],wealso
wantmoreevidencestoconfirm thathigherASC,
GSH,orNADPHaremoreabletoresistCdtoxicity.
1 Materialsandmethods
11 Plantmaterialsandcultureconditions
Stable inheritance rice (Oriza sativa L.)
cadmiumsensitivemutant(cadB1)andthesamerice
varietywildtype(WT)wereusedinthisexperiment.
Theseedsweresurfacesterilizedin05% sodium
hypochloritefor20min,rinsed,andgerminatedinthe
darkonmoistenedfilterpaperat30℃ for2d,and
thenmovedtoaplasticscreenfloatingondistiled
waterat28℃ for4d.Thenuniformlygerminated
seedlingsweretransferedtoblackpolyethylenebarels
whichcontained6Lofriceculturesolution.Seedlings
weregrowninagrowthchamberwithaphotoflux
densityof500μmol/(m2·s),relativehumidityof
approximately65% andday/nighttemperaturesof
32℃/27℃ (14h/10h).Duringthegrowthperiod,
thesolutionwasrenewedevery5d.Atthesevenleaf
743
植 物 营 养 与 肥 料 学 报 21卷
stage,riceseedlingsincludewildtype(WT)and
cadB1exposedto05mmol/LCdCl2 for0(as
control),2,4,6,8,or12d.
12 CdandH2O2contentanalysis
TheCdcontentsinseedlingleaves,stemsand
rootsweredeterminedaccordingtothemethodofShah
andDubey[13].H2O2contentwasdeterminedaccording
tothemethoddescribedbyJanaandChoudhuri[14].
13  RatiosofASC/DHA, GSH/GSSG and
NADPH/NADP+analysis
  ASCandDHAcontentweredeterminedaccording
tothemethodofLawetal.[15].GSHandGSSGcontent
wasdeterminedaccordingtothemethodofAndersonet
al.[16].NADPHandNADP+contentwasdetermined
accordingtothemethodofNisselbaumandGree[17].
14 Enzymeassays
Frozenmaterials(400mgfreshweight)were
homogenizedin 4 mL of50 mmol/L potassium
phosphatebufer,pH78,containing01% TritonX
100Thehomogenatewascentrifugedat15,000×gfor
20minat4℃ andthesupernatantwasusedforenzyme
assays.APX and GR activitiesweredetermined
accordingtothemethodofNakanoetal.[18].DHAR
activitywasdeterminedaccordingtothemethodof
Daltonetal.[19].NDHAR activitywasdetermined
accordingtothemethodofArigonietal.[20].
15 StatisticalAnalysis
Datawereanalyzedwiththestatisticalpackage
SPSS15forWindowsonthewebsite(www.nbs.ntu.edu.
sg/userguide/SPSS/SPSS15/).Significancelevels005
and001wereusedinpresentingtheresults.The
experimentswererepeatedintriplicate,andthedata
presentedarethemeanvalues±standarderor(SE).
ThediferencewasconsideredsignificantatPlevels
lowerthan005(P<005)andthissignificanceis
denotedinthefiguresbyanasterisk()while
significantatPlevelslowerthan001(P<001)
denotedinthefiguresbydoubleasterisk().
2 Results
21 Cadmium accumulationandefectonrice
seedlinggrowth
  Atthesevenleafstage,CdCl2wasaddedtothe
nutrientsolutiontoachievethefinalCd2+concentration
is05mmol/L.After12dexposuretoCd2+,the
leavesofcadB1fadedseriouslyandtherootswere
moreexiguousthanWT.Thefreshweightofshoots,
androotsofwildtypeseedlingsdeclinedby4597%,
and4699%,respectively,whilethepercentdecrease
ofcadB1are6356% and5128%,comparedtothe
controlcultivatedseedlings(Table1).
表1 侵染于05mmol/LCd2+12天后野生型(WT)和Cd敏感型(cadB1)水稻秧苗不同部位鲜重(g,FW)
Table1 Freshweights(FW)ofdiferentorgansofwildtype(WT)andCdsensitive
(cadB1)riceseedlingsafter12dofexposureto05mmol/LCd2+
处理
Treatment
地上部 Shoot
WT cadB1
根 Root
WT cadB1
对照CK 372±010 365±009 083±005 078±003
镉处理 Cr2+treatment 201±014 133±023 044±005 038±005
  TheCdcontentsincreasedinalorgansofboth
WTandcadB1with05mmol/LCd2+exposurefor12
d(Table2).Alargerincreasewasseeninalorgans
ofcadB1comparedtoWTseedlings.However,the
increasewasnotstatisticalysignificant.
22 H2O2accumulationinriceseedlings
H2O2contentsincreasedintheleavesofWTand
cadB1riceseedlingsduringCd2+ exposureperiod
(Fig.1). In general, cadB1 rice seedlings
accumulatedmoreH2O2 thanWT riceseedlings,
exceptthe2ndday.SignificantdiferenceofH2O2
contentsbetweenWTandcadB1riceseedlingleaves
wasonlydetectedthe12thexposureday.
843
2期    沈国明,等:Cd2+诱导的镉敏感水稻突变体cadB1叶片抗坏血酸循环的变化
表2 侵染于05mmol/LCd2+12天后野生型(WT)和Cd-敏感型(cadB1)
水稻秧苗根茎叶中Cd含量 (mg/kg,DW)
Table2 Cadmiumcontentinleaves,stemsandrootsinwildtype(WT)andCdsensitive(cadB1)
riceseedlingsafter12dofexposureto05mmol/LCd2+
处理
Treatment
叶 Leaf
WT cadB1
茎 Stem
WT cadB1
根 Root
WT cadB1
对照CK 619±082 842±028 1696±103 1526±121 2195±114 2204±098
镉处理 Cd2+treatment 7233±115 8821±192 34056±332 38198±231168542±476 189818±532
图1 野生型(WT)和Cd-敏感型(cadB1)水稻秧苗
叶片中H2O2含量
Fig.1 H2O2contentsinleavesofWTandcadB1
riceseedlings
[注(Note):ExternalCd2+concentrationis05mmol/L外源 Cd2+
浓度为05mmol/L.Erorbarsrepresentstandarderor(n=3)误差
线代表标准差(n=3)].
23 CdefectonratiosofASC/DHA,GSH/
GSSGandNADPH/NADP+inriceseedlings
  Duringexposureperiod,leafcontentsofASC
decreasedbothinWTandcadB1(Fig.2a),however
theoppositeefectwasobservedwithDHAcontentsin
leaves(Fig.2b).Significantdiferenceswereseenin
ASCcontentbetweenWTandcadB1riceseedling
leavesatthe8thand12thexposureday.Therefore,
theratioofASC/DHAwasreducedwithprolonging
exposuretime(Fig.2c).Furthermore,inWTand
cadB1riceseedlingstheratiovariedconcomitantly
withprolongingtimeat05mmol/LCd2+.After12d
exposureto05mmol/LCd2+,theratioofASC/DHA
atthe2nd,4th,6th,8thand12thexposureday
compared to the control declined by 976%,
2010%, 3800%, 5300% and 6655%,
respectivelyintheleavesofWTriceseedlings,while
incadB1riceseedlingsthepercentageofdecreasewas
1656%, 3292%, 4857%, 6586% and
8506%,respectively.Overal,theratioofASC:
DHAdeclinedmoreinleavesofcadB1riceseedlings
thaninWTriceseedlings.
TheGSHcontentsdecreaseandGSSGincreasein
leavesoccurednotonlyinWTbutalsoincadB1
duringtheexposure(Fig.2d,e).Significant
diferencestookplaceinGSHcontentsbutnotinGSSG
betweenWTandcadB1riceseedlingleavesduring
exposureperiod.ChangesinGSHandGSSGledto
changesinGSH/GSSGratio(Fig.2f),significant
diferencescouldbefoundintheGSH/GSSGratio
betweenWTandcadB1riceseedlingleavesatthe
4th,8thand12thexposureday.Duringexposure
period,theGSH/GSSGratioinleavesofcadB1rice
seedlingsdeclinedby3580%,6109%,7065%,
8231% and8591%,respectively,whileratiosfor
leavesoftheWTriceseedlingswereincreasedby
2637%, 3752%, 5915%, 6300% and
6809%,respectivelycomparedtothecontrol.GSH/
GSSGratiosdecreasedmoreincadB1riceseedlings
thaninWTriceseedlings.
Oxidized nicotinamide adenine dinucleotide
phosphate (NADP+) contents increased during
exposureperiod(Fig.2h),whiletheNADPH
contentsmeettheoppositetoNADP+ inleaves.
NADPH:NADP+ ratioswerereduced(Fig.2i),
similartoGSH/GSSG andASC/DHA ratios.The
leavesofcadB1riceseedlingsshowedadecreasein
theNADPH/NADP+ ratiosof777%,1934%,
3576%,5503%,and6794%,respectively.In
the WT seedlings, the NADPH/NADP+ ratios
943
植 物 营 养 与 肥 料 学 报 21卷
comparedtothecontrolweredecreasedby381%,
1830%,2876%,4509%,and5837%.The
decreaseintheNADPH/NADP+ ratioswasmore
pronouncedincadB1riceseedlingsthaninWTrice
seedlings.
图2 野生型(WT)和Cd-敏感型(cadB1)水稻秧苗叶片中ASC、DHA、GSH、GSSG、NADPH、NADP+
值和ASC/DHA,GSH/GSSGandNADPH/NADP+比率
Fig.2 ThecontesntASC,DHA,GSH,GSSG,NADPH,NADP+andtheratioofASC/DHA,GSH/GSSG
andNADPH/NADP+inleavesofWTandcadB1riceseedlings
[注(Note):外源Cd浓度为05mmol/LExternalCdconcentrationis05mmol/L;P<005andP<001误差线代表标准差(n=3)
Erorbarsrepresentstandarderor(n=3).]
24 CdefectonAPX,GR,DHARandMDHAR
activitiesinriceseedlings
  APXactivitiesincreasedandthendecreasedboth
inWTandincadB1riceseedlingsduringexposure
(Fig.3a).APXactivityreacheditshighestlevelin
WTandincadB1riceseedlingsatthe6thexposure
day, and the APX activitiesshowed significant
diferencesbetweenWTandcadB1riceseedling.
APXactivitiesdecreasedmoreintheleavesofcadB1
seedlingsthaninWTseedlingsduringexposure.
GRactivitiesincreasedfirstandthendecreasedin
both WT and cadB1 rice seedlings with the
prolongationofexposure(Fig.3b).GR activities
werehighestinbothWTandcadB1riceseedlingsat
the4thexposureday,GRactivitieswereobserved
higherinWTthanincadB1riceseedlings.to05
mmol/LCd2+,onthe4thdayofexprosure,comparing
tothecontrol,GRactivitiesincreasedby6485% in
cadB1seedlingsand101% intheWTriceseedlings.
Atthe8thday,significantdiferencesinGRactivities
wereobservedbetweencadB1 andtheWT rice
seedling.
Inthisexperiment,DHARactivitieswerelowerin
cadB1thaninWTseedlingswithCd2+exposure(Fig.
053
2期    沈国明,等:Cd2+诱导的镉敏感水稻突变体cadB1叶片抗坏血酸循环的变化
3c).DHARactivitiesintheWTincreasedandthen
decreased,cadB1variedconcomitantlywithWT.In
thecadB1riceseedlings,DHARactivitiesreached
maximumlevelsatthe4thexposureday,whilethosein
WTseedlingsreachedmaximumlevelsatthe8thday.
DiferencesinDHARactivitiesbetweencadB1and
WTplantsweresignificantatthe6th,8thand12th
exposureday.
MDHARactivitiesincreasedandthendecreased
bothinthecadB1andWTriceseedlings(Fig.3d).
MDHARactivitiesweremaximumatthe4thdayin
cadB1,andatthe6thdayinWTseedlings.MDHAR
activitiesdecreasedmoreinthecadB1thantheWT
riceseedlings.Atthe12thexposureday,MDHAR
activitiesdecreasedby5682% intheMT,and
4779% inthecadB1.MDHARactivitydiferences
weresignificantbetweencadB1andWTriceseedlings
atthe6thexposureday.
图3 野生型(WT)和Cd-敏感型(cadB1)水稻秧苗根系中APX,GR,DHARandMDHAR活性
Fig.3 APX,GR,DHARandMDHARactivitiesinrootsofWTandcadH5riceseedlings
[注(Note):外源Cd浓度为05mmol/LExternalCdconcentrationis05mmol/L;—P<005;—P<001误差线代表标准差 (n=3)
Erorbarsrepresentstandarderor(n=3).]
3 Discussion
H2O2 isinduced in Arabidopistreated with
Cd2+[21],moreover,H2O2considered,asasignaling
moleculeinstress,isweldocumented[22],itdefense
andprovideacclimationduringvariousabioticand
bioticstresses.Ingeneral,wefoundtheH2O2contents
increasedwithprolongationofCd2+ exposureinboth
cadB1andWTplants,andaccumulatedmorein
cadB1thaninWT(Fig.1).
GSHhasbeentodemonstratedplayakeyrolein
defense mechanisms[23]. It can aleviate H2O2
immediatelyorparticipateintheASCGSHcycleto
scavengeH2O
[24]
2 GSHhasbeenshowntocombine
withCu2+andaleviateCu2+toxicity,GSHisalsothe
substrateforphytochelatin(PC)synthesis,which
playsacentralroleinmetaldetoxification[23].GSHis
oxidizedtoGSSGandthebalanceofGSHandGSSGis
crucialfortheenzymaticsystemsthatscavengeH2O2
A common responsetoheavymetalexposureis
depletionofGSHandasubsequentriseinGSSG[25].
Here,theGSHcontentwasslightlydecreasedbothin
cadB1andWTinshorttimeexposure.Whenthe
exposureprolonged,theGSH contentwentdown,
particularlyinthemutant,andtheGSSG content
increased.ThustheGSH/GSSGratiodecreasedwith
153
植 物 营 养 与 肥 料 学 报 21卷
increasingCd2+ concentrations(Fig.2f).Atshort
timeCd2+ exposure,GSH contentdecreasedonly
slightly,suggestingonewayplantsmightadapttoCd2+
stress.Plantscanusethisabilitytoselfadjustand
enhanceresistancetoCd2+ stressin shorttime
exposure.Withtheexposuretimeprolonged,GSH
contentdecreaseddramaticaly,perhapsbecauseit
atachestoheavymetals,orprovidesasubstratefor
PCssynthesis.Alternatively,itmaybehaveasa
antioxidanttoscavengeROS,oritmayhavelower
NADPH,whichmaybeascribedtothecoresponding
decreaseinGRactivity,andtheresultingdecreasein
GSH.Duringourstudy,thelowerGSHcontentsin
cadB1thanWTmaybeduetothelowerGRactivityor
theloweractivityofγglutamylcysteinesynthetase(γ
ECS)andglutathionesynthetase(GS).Thelower
GSHcontentsandGSH/GSSGratiomaybeonereason
whythemutantismoresensitivetoCd2+toxicity.
ASC behavesasanelectrondonorforAPX
scavengingofH2O2,andwouldbeoxidatedtoDHA.
Ontheotherhand,DHAcouldberegeneratedtoASC
byDHAR,usingGSH asanelectrondonor.The
balanceofASCandDHAiscrucialfortheenzymatic
systemsthatscavengeH2O2Inthepresentstudy,we
foundthatprolongedCd2+exposuretimeproduceda
decreaseintheASCcontentwhileincreasedinthe
DHAcontentbothincadB1andWT.Thesechanges
resultedindecreasesintheASC:HA ratio.The
decreaseinASCcontentmightbeduetoaninhibition
oftheDHARactivity,ormoreexcessiveuseofASCin
metaldetoxification,orbecausetheactivityofGSH,
anelectrondonor,islower.TheASCcontentandthe
ASC:DHAratiowerelowerinthemutantthaninthe
wildtype.ThiscouldbetheresultoflowerDHAR
activitiesincadB1thaninthewildtype(Fig.3).
Fromthis,weinferedthatplantsresistanttoCd2+
toxicitymaintainahighASCcontentandrequireahigh
ratioofASC/DHA.
H2O2scavengingbyAPXisthefirststepinthe
ASCGSH cycle[26]. As demonstrated in the
choroplastsofpea(Pisum sativum) andspinach
(Spinaceaoleracea),GR,DHAR,andMDHARalso
participateinthiscycle[26].Inthisstudy,wefoundat
theshorttimeofCd2+ exposurecaninduceAPX
activity,and may indicate the H2O2 contentis
increasing;afterlongtimeofCd2+ exposuretheAPX
activitiesdecreased,whichnotsuggestingtheH2O2
contentisdecreasingbutshowingCd2+ inhibitionof
APXactivities.Withtheprolongationofexposure,
APXactivityreductionsweremorepronouncedinthe
mutantthaninthewildtype,showingthatCd2+
stronglyinhibitsAPX activityinthemutant.GR
activitiesvaryconcomitantlywithAPXactivities;short
timeCd2+ exposurecaninduceGRactivities,which
catalyzeGSSG to synthesize GSH by consuming
NADPHasanelectrondonor.DHARandMDHAR
takepartintheregenerationofASC.Atfirstcan
induceDHARandMDHARactivity,possiblyasthe
resultofincreasedAPXactivities,henceDHARand
MDHARcaughtregenerateenoughASCasanelectron
donorforAPXscavengingforH2O2Withlongtimeof
Cd2+,DHARandMDHARactivitiesareinhibited,
andDHARandMDHARactivitiesdecreasemorein
themutantthaninthewildtype,showingthatCd2+
inhibitedbothDHARandMDHARactivitiesinthe
mutantacutely.Attheshorttime,ROSisefectively
scavenged;atthelongtimethecapabilityisoveridden
andtheycannotscavengeROSefectively.Fromthis
weinferedtheplantisireversiblydamagedand
inhibitedbyROSatthelongtimetoCd2+exposure.
4 Conclusion
ThehigherASC,GSHandNADPHlevelsandthe
higherratiosofASC/DHA,GSH/GSSGandNADPH/
NADP+,aswelasthehigherantioxidativeenzymatic
activitiesinplantswilbemoreefectivetoresistCd2+
toxicity.ComparetoWT,themutantcadB1haslower
levelofantioxidantsaswel asloweractivityof
antioxidantenzymes;AlitlemoreCdaccumulatedin
cadB1meansalitlemorereactiveoxygenspecies
production(ROS).Videlicet,cadB1isdeficientof
thedefensepoweragainstincreasedlevelofROSwhich
leadstoalowergrowthpotentialandsensitivetoCd.
Acknowledgements:
TheauthorsareverygratefultoDrWangJiang
Xin(Shenzhen University) read the manuscript
carefuly,andproposedmanyrevisions.Thiswork
253
2期    沈国明,等:Cd2+诱导的镉敏感水稻突变体cadB1叶片抗坏血酸循环的变化
supported by Heze University fund to PhD
(XY13BS01).
References:
[1] LiuYG,WangX,ZengGMetal.Cadmiuminducedoxidative
stressandresponseoftheascorbateglutathionecycleinBechmeria
nivea(L.)Gaud[J].Chemosphere,2007,69(1):99-107
[2] AnjumAN,GilSS,GilR etal.Metal/metaloidstress
toleranceinplants:roleofascorbate,itsredoxcouple,and
associatedenzymes[J].Protoplasma,2014,251(6):1265
-1283
[3] LiZ,SuD,LeiBetal.Transcriptionalprofileofgenesinvolved
inascorbateglutathionecycleinsenescingleavesforanearly
senescenceleaf(esl) ricemutant[J].JournalofPlant
Physiology,2014,176(25):1-15
[4] ChaparzadehN D,AmicoM L,KhavariNejadR A etal.
AntioxidativeresponsesofCalendulaoficinalisundersalinity
conditions[J].PlantPhysiologyandBiochemistry,2004,42(9):
695-701
[5] KuzniakE.MariaS.Ascorbate,glutathioneandrelatedenzymes
inchloroplastsoftomatoleavesinfectedbyBotrytiscinerea[J].
PlantScience,2001,160(4):723-731
[6] KuoMC,KaoCH.Antioxidantenzymeactivitiesareupregulated
inresponsetocadmium insensitive,butnotintolerantrice
(OryzasativaL.)seedlings[J].BotanyBuletinofAcademy
Sinica,2004,45:91-299
[7] SrivastavaS, TripathiR D, DwivediU N. Synthesisof
phytochelatinsandmodulationofantioxidantsinresponseto
cadmiumstressinCuscutareflexa-Anangiospermicparasite[J].
JournalofPlantPhysiology,2004,161(6):665-674
[8] MonrásJP,ColaoB,MolinaQuirozRC,PradenasGAetal.
MicroarayanalysisoftheEscherichiacoliresponsetoCdTeGSH
Quantum Dots:understanding the bacterial toxicity of
semiconductornanoparticles[J].BMC Genomics.2014,15
(1):1099
[9] 林冬,朱诚,孙宗修.镉敏感水稻突变体在镉胁迫下活性氧
代谢的变化[J].环境科学,2006,27(3):561-566
LinD,ZhuC,SunZX.Alterationsofoxidativemetabolism
respondtocadmiumstressinCdsensitivemutantriceseedlings
[J].EnvironmentalSciences2006,27(3):561-566.
[10] HeJY,ZhuC,RenYFetal.Rootmorphologyandcadmium
uptakekineticsofthecadmiumsensitivericemutant[J].
BiologiaPlantarum,2007,51(4):791-794
[11] ShenGM,ZhuC,DuQZ,ShangguanLN.Ascorbate-
Glutathionecyclealterationinacadmiumsensitivemutantfrom
rice[J].RiceScience,2012,19(3):185-192
[12] ShenGM,ZhuC,ShangguanLN,DuQZ.TheCdtolerant
ricemutantcadH5isahighCdaccumulatorandshowsenhanced
antioxidantactivity[J].JournalofPlantNutritionandSoil
Science,2012,175(2):309-318
[13] ShahK,DubeyRS.A18kDacadmium inducibleprotein
Complex:itsisolationandcharacterisationfrom rice(Oryza
sativaL.)seedlings[J].JournalofPlantPhysiology,1998,152
(4):448-454
[14] JanaS, ChoudhuriM A. Glycolatemetabolism ofthree
submersedaquaticangiospermsduringaging[J].Aquatic
Botany,1982,12:345-354
[15] LawMY,CharlesSA,HaliwelB.Glutathioneandascorbic
acidinspinach(Spinaciaoleracea)chloroplasts.Theefectof
hydrogenperoxideandofParaquat[J].BiochemistryJournal,
1983,210:899-903
[16] AndersonJV,ChevoneBI,HessJL.Seasonalvariationinthe
antioxidantsystem ofeasternwhitepineneedlesevidencefor
thermaldependence[J].PlantPhysiology,1992,98(2):501-
508
[17] NisselbaumJS,GreenS.A simpleultramicromethodfor
determinationofpyridinenucleotidesintissues[J].Analytical
Biochemistry,1969,27(2):212-217
[18] NakanoY,ASCdaK.Purificationofascorbateperoxidasein
spinach chloroplasts; itsinactivation in ascorbatedepleted
mediumandreactivationbymonodehydroascorbateradical[J].
PlantandCelPhysiology,1987,28(1):131-140
[19] DaltonDA,RusselSA,HanusFJetal.Enzymaticreactions
ofascorbateandglutathionethatpreventperoxidedamagein
soybeanrootnodules[J].ProceedingsoftheNationalAcademy
ofSciences,1986,83(11):3811-3815
[20] ArigoniO,DipieroS,BoraccinoG.Ascorbatefreeradical
recuctase:Akeyenzymeofascorbicacidsystem[J].FEBS
Leters,1981,125:242-244
[21] ChoU,SeoN.OxidativestressinArabidopsisthalianaexposed
tocadmiumisduetohydrogenperoxideaccumulation[J].Plant
Science,2005,168(1):113-120
[22] ChenC,TwitoS,MilerG.NewcrosstalkbetweenROS,ABA
andauxincontrolingseedmaturationandgerminationunraveled
inAPX6deficientArabidopsisseeds[J].PlantSignal&
Behavior,2014,9(12):e976489
[23] CobbetC,GoldsbroughP.Phytochelatinsandmetalothioneins:
rolesinheavymetaldetoxificationandhomeostasis[J].Annual
ReviewofPlantBiology,2002,53(1):159-182
[24] DaltonDA,RusselSA,HanusFJetal.Enzymaticreactions
ofascorbateandglutathionethatpreventperoxidedamagein
soybeanrootnodules[J].ProceedingsoftheNationalAcademy
ofSciences,1986,83(11):3811-3815
[25] OrtegaVilASCnteC,RelánálvarezR,DelCampoFFetal.
CelulardamageinducedbycadmiumandmercuryinMedicago
sativa[J].JournalofExperimentalBotany,2005,56(418):
2239-2251
[26] JimenezA,HernandezJA,DelRioLA,SevilaF.Evidence
forthepresenceoftheascorbateglutathionecycleinmitochondria
andperoxisomesofpealeaves[J].PlantPhysiology,1997,114
(1):275-284
353