植物生理学教学课件：chapter09 Plant Senescence and Organ Abscission

Chapter9PlantSenescenceandOrganAbscission

Section1PlantSenescenceanditsprogram1.1Conceptandtypesofplantsenescence1.1.1Senescence:Aprograminwhichthefunctionoforganorwholeplantnaturallydeclinestodeath.Thisisanessentialphaseofthegrowthanddevelopmentinplant。Fornutritiontransfer,suchasseed，tuberandbulb。Leafabscissioninfall——sprout，leafandflowergrowinnextspring。Fruitsmatureandfall——seedsspread。

1.1.2typesofplantsenescence

(1)OverallSenescenceSenescenceoccursinwholeplantbody,suchasannualswhichsenescestodeathafterflowerandsetting.(2)TopSenescenceThepartabovegrounddieswiththeendofgrowthseason,butthepartundergroundisaliveforseveralyears.Perennialweeds,corm(球茎)andbulb（鳞茎）——lily。InsummerInwinter(3)DeciduoussenescenceTheleaffallsinspeciousseason,insummerorwinter.Deciduoustrees(4)ProgressivesenescenceSenescenceonlyoccursinolderorganortissue.Neworganortissuedevelopswhileoldonesaresenescing.Greentrees。衰老有其积极的生物学意义，不仅能使植物适应不良环境条件，而且对物种进化起重要作用。温带落叶树的叶片，在冬前全树叶片脱落，从而降低蒸腾作用，有利于安全越冬。通常植物在衰老时，其营养器官中的物质降解、撤退并再分配到种子、块茎和球茎等新生器官中去。如花的衰老及其衰老部分的养分撤离，能使受精胚珠正常发育；果实成熟衰老使得种子充实，有利于繁衍后代。1.2ProgramforplantsenescenceSenescencecanoccuratdifferentlevels:cell,tissue,organsandwholeplant.1.2.1Cellsenescence

Membraneandorganellesenescence。、Senescenceincellmembrane。(1)Lipidphasechange。Biomembranechangesitsphasefromliquid-crystallinestatetosolid-gelstate.

Hardandinextensive，fluiditydecreasesandcohesionincreases。液晶相凝固相衰老、低温六方晶相I六方晶相II混合相衰老生物膜几种相变示图liquid-crystallinestatesolid-gelstate（2）DegradationandperoxidationoflipidleadtodecreaseinlipidcontentSynthesis↓,lipase↑,

phospholipase、lipoxygenaseandactiveO2↑MDA(malonyldialdehyde）↑。

（3）Phospholipase

。磷脂酶A1、磷脂酶A2、磷脂酶B、磷脂酶C、磷脂酶D等。其中，磷脂酶D主要存在于高等植物组织中。CH2—O—C—R1CHCH2—O—P—O-XR2—C—OOOOOHA1A2BCDThedehydrationboundfordifferentphospholipasesPhospholipid

↓phospholipaseAorBPolydouble-boundfatacid

↓Lox(lipoxygenase)OrganicfreeradicalsR’HC=CCH2C=CR’’-COOHHHH顺，顺—甲叉间二烯R’HC=CCHC=CR’’-COOHHHH•O2OOH•夺取氢，形成过氧自由基R’HC=CCHC=CR’’-COOHHHH•自由基：反，顺—共轭二烯重排OOH•R’HC=CCHC=CR’’-COOHHHHOOH过氧化作用反，顺—共轭二烯过氧化物（4）Biomembranedegradationandleakage.Lossequilibriumofionsanddisorderofmetabolism。、Organellesenescence。

RibosomeandroughER↓→chloroplastsbreakdown→mitochondriacristaeswollen↑→vacuolebroken.Autophagyoccursandcellsenescesanddegrades.1.2.2Programmedcelldeath(PCD，程序性细胞死亡)Theorganismcontrolstheinitiationandexecutionofthecelldeathprocess,thesetypesofcelldeatharereferredtoasprogrammedcelldeath(PCD)PCD可发生在植物的各种细胞。过程：DNA断裂、染色质固缩、胞泡形成、凋亡小体形成。动物细胞PCD后产物被其他细胞吞噬利用，植物细胞PCD后产物用于本身细胞次生壁的构成。OneoftheimportantfunctionsofPCDinplantsisprotectionagainstpathogens.Whenapathogeninfectsaplant,cellsatthesiteoftheinfectionquicklyaccumulatehighconcentrationsoftoxicphenoliccompoundsanddie.Thedeadcellsformasmallcircularislandcalledanecroticlesion,whichisolatesandpreventstheinfectionfromspreadingtosurroundinghealthytissues.Thisrapidandlocaizeddeathduetopathogenattackiscalledthehypersensitiveresponse,whichisageneticallyprogrammedprocess.PCD发生过程启动阶段（initiationstage)启动细胞死亡信号的产生和传递效应阶段(effectorstage)caspase的活化和线粒体通透性的改变。Caspase属于半胱氨酸蛋白酶家族，直接导致PCD细胞原生质解体酶解清除阶段(degradationstage)Fig20.4Celldeathoccursinalmostallplantcellsandtissues.PCDisinvolvedinnumerousprocesses,inclu-dingthefollowingillustrat-edinthisfiguregameteformation,includingmegasporeformation(1);embryodevelopment(2);degenerationoftissuesintheseedandfruit(3);tissueandorgandevelopment(4)through(6);senescence(7);andresponsestoenviron-mentalsignalsandpath-ogens(8and9).Fig20.9SenescenceinArabidopsisthaliana.(A)DevelopmentofArabidopsisthalianaplantsisshownatvarioustimesaftergermination.Photographsshowplantsat14,21,37,and53daysaftergermination(lefttoright).Notetheyellowingofshootsofthe53-day-oldplant.(B)Age-relatedchangesinrosetteleavesofArabidopsis7,9,and11daysafterleafexpansionhadceased.Notetheprogressiveyellowingofleaves,beginningfarthestfromthemainveinsFig20.2(A)Saccharromycescereoisiaeundergoesautophagy(自体吞噬)whenstarvedofnutrients.Theyeastshowninthisfigurewasnitrogen-starved,bringingaboutautophagy,inwhichautophagicbodies(AB)engulfthecytoplasmandtransportittothevacuole(V),whereproteasesandotherlyticenzymesreleasenitrogentocompensateforthelackofnitrogeninthemedium.(B)AutophagyoccursindyingplantcellsasinthesenescingImpomeatricolorcorollacelldiagrammedhere.Autophagicbodiesengulfaportionofcytoplasm,includingthenucleus(N),tothevacuole(s),wherebreakdownofthecell’scontentsoccurs.ThethreecellsshownrepresentdifferentstagesofPCD,Abeingtheearliest,andBandClaterstagesofautophagy.ABFig20.5Theinflorescencesofmaizecontainflowersthatareinitiallybisexual,butPCDresultsinthedeathofmaleorfemaletissuestogiverisetofemaleinflore-scence(ear)ormaleinflorescence(tassel),respectively.Inthetasselseed2mutant(A),femaletissuesinthetasseldonotundergoPCD,andtheresultingtasselflowersaremostlypistilate.Awild-typetasselinincludedforcomparison(B).Fig20.6OnevisibleexampleofPCDinplantsisseenintheornamentalplantMon-steradeliciosa.

Theleavesofthisplantexhibitdeepindentationsandholeinthelamina,whichresultfromthepro-grammeddeathofspecificregionsoftissueinthedevelopingpromor-dia.Astheleafexpands,theseareasarenotreplaced,andtheresultingleaflaminahasthecharacteristicpatternthatinspiresthecommonname,‘‘Swisscheeseplant’’Fig20.8Aerechymaformationinmaizerootsinresponsetohypoxia.Rootsweregrownunderareobic(A)andhypoxic(B)conditions.Underlow-oxygenconditions,corticalcellsbetweentheendodermisandhypodermisundergolysogenictoformairspacesthatarecontinuousthroughouttheroot,therebyallowingsubmergedrootsaccesstoatmosphericgasesobtainedbyabove-groundtissues.

1.2.3OrganSenescence

Leafsenescence。（1）Photosynthesisdeclines-----slowerphaseandfasterphase。Decreaseinactivityandcontentofphotosynthetickeyenzyme(Rubisco)Decreaseinactivityofphotoelectrontransportandphotophosphorylation.Decreaseinstomatalconductance.Decreaseinchlorophyll.Leafyellow.Organelledegradation:叶绿体内基粒→（脂类小体）→内质网→核糖体→线粒体→液泡膜。相对值大小呼吸速率可溶性氮化物蛋白质叶绿素含量光化学活性光合速率Rubisco活力天叶片衰老期间的生理变化示意图脂质小体Fig20.13Impactofsenescenceonplastidultrastructureinleavesofwild-typeandastay-greenmutantoftheC3grassX.Festulolium.(A)Priortosenescence,thechloroplastsofawild-typeandmutantplantscontainnumerousgrana,stacksofappressedthylakoidmembranes.(B)Theseinternalmembranestructuresarelostduringsenescenceofawild-typemesophyllcell,andelectron-denselipiddropletsknownasplastoglobuliaccumulate.(C)Retentionofintrinsicthylakoidmembraneproteins,pigments,andotherhydrophobiccomponentsgivesthegerontoplasts(老年质体)ofmutanttissuesadistinctiveappearance,withpersistentgranastacksandfewplastoglobuli.Fig20.15Chlorophyllaanditsbreakdownproducts.Subcellularcompart-mentationofthepheo-phorbideapathwayofchlorophyllcatabolisminleafmesophyllcells.Fig20.19(A)Activityofkeychlorophyll-catabolizingenzymePaOisstronglyinducedinsenescingtissuesofwild-typeX.Festuloliumbutundetectableinpresenescentleavesandinastay-greenmutant.(B)Inductionofchlorophylldegradationinwild-typetissueisaccompaniedbylossofthepigment-bindingmembraneproteinLHCP,asshownbyWesternblottinganalysis.InthemutantasecondformofLHCPIIprogressivelyaccumulatesassenescenceproceeds.Asillustratedinthecartoon,degradationofLHCPIIwhichprotrudesfromthethylakoidmembraneintothestroma.(C)StabilityofRubisco,themajorstromalprotein,isenhancedveryslightlyinthemutantcomparedtowildtype.Xieyou9308Shanyou63Peiai64s/9311Xieyou9308Shanyou63Peiai64s/9311ABChangesinmRNAsofrbcS(A)andrca(B)inflagleafafterheading

Seedaging。Theviabilityofseedlossinverselyfrommaturetodeath。Degradationandleakageofbiomembrane:MitochondriaandERbecomeswollen,plasmicmembranecontactsanddepartfromcellwall.DNAinjury，broken。Enzymeactivitydecreases:dehydrase。Storagematterexhausting,freefatacidrising.

1.2.4Senescenceinwholeplant：OnesettingplantsPolysettingplants------graduallysenescingSection2SenescenceMechanismandregulation2.1

Senescencecausedbynutritionexhaustion

Nutritionexhaustion

theory：Senescencecausedbyreproductiveorgan.Suchastomato,ifsetting,survivesforoneseason,ifflowerremovedoff,survivesforseveralyear.Roottissueculture,morethan30years.龙舌兰doesnotflower,liveforseveraldecades,andfloweringalive—8-10years。Oppositeviews:Sunflowersenescespriortoflowerinitiation.Removingfloweracceleratessenescenceinmaizeandpopper自由基损伤学说：自由基有细胞杀手之称。1955年哈曼（Harman）就提出，衰老过程是细胞和组织中不断进行着的自由基损伤反应的总和。

2.2Physiologyandbiochemistryduringsenescence

2.2.1Senescence-associatedgenes（SAGs）expression。

Senescenceiscontrolledbyspecialgenes.Twokindsofgenescanbefoundduringsenescence.(1)Senescence-downwardgenes，mostofgenescodeenzymesrelevanttophotosynthesis,energymetabolismandothersynthesis。(2)Senescence-upwardgenes，mostofgenescodeenzymesforhydrolase,suchasDNase,RNase,Protease,phospholipase。Senescence-associatedgenes（SAGs）referstotheirmRNAlevelsincreasewithsenescenceproceeding.Theyfunctioninmetabolismofbiomacromoleculedegradationandmobilization.Morethan40geneshavebeencloned:ProteasesinMaize,A.thaliana,rape.SAG2,See1,LSC7，SAG12，LSC790，LSC760；RNS1，RNS2，RNS3in

A.thaliana

；PEPC，MDH，MS，ICL，GAPDH,F-1,6-P,aldolaseandβ—galactosidaseinrape,cornandcucumber.StagesinBrassicanapusleafsenescence.SAGsaredividedinto10classesaccordingtotheirtemporalpatternofexpression.2.2.2Degradationofbiomacromolecules。(1).DNAdegrades，RNAchangesinqualityandquantity.RNAbreakdownfasterthanDNAdoesduringsenescence,especiallyrRNA,whichismoresensitivetosenescence.RNaseactivityrisesandDNA—RNApolymeraseactivitydeclines。(2).Proteinsynthesisdecreasesanditsdegradationincreases。Solubleprotein-----Rubiscodecreasesin85%,thylakoidmembraneproteindecrease50%,andcytochromef,bdecreasesfast。Twopossiblemechanismsareillustrated.Inonecase(leftsideoffig.),occupationofbindingsitesbycofactors(e.g.,enzymesubstrates)orallostericeffectorslockstheproteinintoaconformationresistanttoproteolysis,andtheequilibriumbetweenthisstructureandthesusceptibleconformationisthusdeterminedbytheabundanceoftheseligands.Intheothercase(rightside),theproteinismarkedfordegradationbytheadditionofatagsuchasubiquitinandistherebymadeavailableforproteolysis.Fig20.20Comparisonofthe

foliarsenescence-as-sociatedproteaseSEE1frommaizewithothercysteineendopeptidases.

(A)TheaminoacidsequenceinferredfromSee1cDNAalignedwiththesequencesofotherproteasesfromthesamefamily.Conservedstructurefea-turesincludingaputativevacuolesortingmotif(residues29through34;redline),potentialglyco-sylationsites(125throu-gh127,256through258;bluelines),andthelikelycleavagepointthatremovestheprodomain(between142and143;arrowhead).Opencirclesindicatethecysteine-histidine-asparaginetriadoftheactivesite,andthegreenlinesidentitifythesurroundingconservedregions.(B)DendrogramlocatingSEE1inthesamesubfamilyasthecerealgerminationproteasesaleurainandoryzain.NotethatSAG12ofgreeofconservationofcysteineproteasestructuralmotifsinSEE1allowsathree-dimensionalmodeltobedevised.

GluconeogenesisinsenescingleleafcellsTheglyoxylatebypassisactivated(3).biomembranebreakdownsandlossesitsfunction.2.2.3Disorderofplantgrowthsubstance（1）、CTKcontentdecreases。Detached(invitro)leaf----aggravatingsenescence;Rooting----RegreeningHigherCTKcontentsofthebleedingsapintheresist-senescingcultivarsinsunflowerandrice

CTKfunctions:Blockingsomesenescence-associatedgenes(SAGs)expression;Preventinghighbiomoleculesfromdegradation;Delayingdeclinationofphotosynthesisandmaintainingregularrespiration;Makingthestomataopen;Cleaningfreeradicalsandchangingassimilatedistribution.（2）Eth.Itinduces“Cyanide-resistantpathway”，andstimulateactiveO2formationaswellashydrolasesynthesisandactivation。Fig20.26Ethylenepromotesleafsenescenceinwild-type(WT)Arabidopsis,butnotintheethylene-insensitiveetr1mutant.Fig20.28Ethyleneproduction(A)andtheexpressionofethylene-inducedgenes(B)inripeningtomatofruit.MG1throughMG4refertosequentialstagesintomatofruitdevelopment.MG,maturegreen;Imm,immature.Theinflorescencein(B)isfromaplantcarryingtheneverripemutation,whichisinsensitivetoethylenebecauseofamutationinanethylenereceptor.Asaresult,ethylenedoesnottriggersenescenceandabscissionintheseflowers.Inuntreatedwild-typeflowers,floralsenescencefollowspollination(C),whereasintheethylene-insensitivemutants,theflowersdonotsenesceafterpollinationbutinsteadremainintact,evenasthefruitbegintodevelop(D).Thus,ethyleneisakeysignalininducingfloralsenescenceafterpollinationintomato.Asthenameimplies,intheneverripemutant,thefruitdonotripen.Thetwotomatofruitsin(E)areofapproximatelythesameageandweregrownunderthesameconditions.However,thefruitontheleftisfromaneverripemutant,whereasthefruitontherightisfromthewild-typeplant,thusemphasizingtheimportaceofethylenesignalingintheinductionofrepeningFig20.29Exogenoustreatmentwithethyle-neinducessenescenceinmanyplants.Thetomatoinflorescenceontheleftin(A)wastreatedwithethylene,causingtheflowerstosenesceandabscise.wwwnrnrnrEthylenesynthesisbyleavesofcontrol(Blue)orantisenesce(red)tomatoplantsexpressingACCsynthase.MethionineSAM(S-Adenosylmethionine)SAMdecarboxylaseACCsynthaseSpd(spermidine)ACCSpm(spermine)EthFigSyntheticcompetitionofployaminetoEth

(3)ABA.

Stomatalclosureandhydrolasesynthesis

(4)JAJA(Me-JA):chlorophylldegradationandEthpromotion.2.2.4EquilibriumlossofCa2+betweenintro-andextra-cell

。UsuallyCa2+8-15mmol/Linapoplastand0.1-1μmol/Lincytoplasm.Ca2+entersthecytoplasmandcausessenescenceActivatingCaM,phospholipaseDActivatingphospholipaseAPhospholipiddegradationUnsaturatedfatacidBD,CaenterscellHydroylsuperoxidefatacid(Cachannel)LoxPhospholipidCachannel

Primaryreaction（

）andsecondaryreaction（）ofbiomembranedegradation(BD)inducedbyCaandCaM2.2.5、Freeradicalsburstandthecapacitiesofscavengersystemsdecline.

feedradical

Freeradicals:ion,atomandmoleculewithfreeelectron.

Characters：instable,active,stronglyoxidativecapacityandchain-reactionsInorganicfreeredicals:、1O2andOH；Organicfreeredicals:ROO、RO。O2Mostofinorganicfreeradicalsfromtheilluminatedchroloplast(1)Photochemicalfreeredicals---hvPSIIPSIO2MehlerreactionO2O2e-e-XanthineoxidaseO2OHO2(2)Xanthine+uricacid++H2O+O2+(3)Fentonreaction：OHH2O2+Fe2++OH-+Fe3+(4)Haber-WeissreactionO2OHH2O2++OH-+O2OHisthemostpoisonfreeradicalinthelivingthingsFreeradicalscavengingsystemsinplant(1)Non-protectiveenzymesystem—antioxidant:Cytf、glutathione、ascorbicacid、ubiquinone,vitaminEandcarotenoids。(2)ProtectiveenzymesystemsSOD、AAO、glutathionereductase、catalaseandglutathioneperoxidase.SODismostimportant.SODtypes:(1)CuandZn—SOD，dimmerwithsubunit32kD，andeachwithoneCu2+andZn+，mainlydistributesinhigherplantchloroplast(2)Mn—SODmainlydistributesinprokaryoticbacteriaaswellineucaryoticmitochondria(3)Fe—SODisabasictype，mainlylocatesingreenalga.SODcatalyticreaction：O22+2H2OH2O2+O2SODFig20.24Theassociate-glutathioneredoxcycleinsenescence.Ascorbateisregeneratedfromoxidizedformsbyacyclecatalyzedbyascorbateperoxidase(APX),monodehydroascor-batereductase(MDHAR),dehydroascorbatereductase(DHAR),andglutathionereductase(GR).Superoxidedimutase(SOD)isoneoftheenzymaticdefensesagainstthebuildupofreac-tiveoxygenspecies.Inma-tureleaves,photosyntheticelectrontransfergeneratesNADPH,whichdonateselectronstoascorbatebywayofreducedglutathione(GSH).Insenescingleaves,NADPHproductiondecreases,resultinginincreasedratiosofoxidizedglutathione(GSSG)toGSHandofdehydroascorbatetoascorbate.Theserelativelysubtlechangescanresultinsubstantialchangesincellularredoxconditionsandsignalnewpatternsofgeneexpression.PSI,PhotosystemI;*,nonenzymaticreaction.Section3MechanismforAbscissionAbscission:

aprocessduringwhichthecells,tissuesororgans,suchasflowers,fruitsandsmallbraches,aredetachedfromtheplantbody.Normalabscissioncausedbysenescenceorripening.Abnormalabscissioncausedbystresses:higherorlowertemperature,droughtorflood,insectsordiseases.Physiologicalabscission

causedbydisordersinphysiologyitself:suchasnutritionalcompetitionbetweenvegetationandregeneration,sinkandsource.Budincottonis70％abscission，flowersorfruitsinsoybeanis60-70%abscission。3.1Abscissioninanatomyandphysiology3.1.1Abscissioninanatomy

AspecificPartforabscission——abscissionzone。Oneorseverallayersofcelllocateinthepetioleinwhichcellshaveasmallinsize,acloseconnectionwitheachother,adensecytoplasmandstarchgrains.DivisioncellChangeincellwallduringabscission中胶层3.1.2Enzymesrelativetoabscission(1)、Cellulase。

Cellulaseactivityincreasesinbean,cottonandcitrusduringleafabscission。

(2)、Pectinase.Inbeanpectinase↑,abscission↑.Pectincompound↓Pectinase(PEM,果胶甲酯酶)Pectin↓Pectinase(PG,多聚半乳糖醛酸酶)Smallsubunit(sugar,C5)(3)、Catalase↑,abscission↑。3.1.3Abscissionandplanthormones(1)、IAAs。

WhenIAAisappliedinthepartoutsideofabscission(远基（轴）端),abscissionpromotes,inotherway,WhenIAAisappliedinthepartinsideofabscission(近基（轴）端),abscissioninhibites.IAApromotionofabscissionIAAprotectionfromabscissionAbscissionzoneCTKandGA?

(2)、Ethylene。

InduceandsecretePG,degradecellwall.(3).ABA。Justbeforethefallingintheautumn，ABA↑.ABAinhibitsIAAtransferandpromotesdehydrolaseactivity。Section4、Environmentalfactorsinfluencingsenescenceandabscission

4.1Temperature

SenescenceandabscissionriseatTtoohighandlow.4.2Water

Senescenceandabscissionriseatdroughtbecauseof1AAoxidation，andCTKdeficiency；EthandABAincrease.Inthefloodingcondition,senescenceandabscissionrise.4.3light

Lightintensity↓,abscission↑.Notenoughphotoassimilate.ShortdayinduceABA,resultinginsenescenceandabscission.

Toohighlightintensity,abscission↑.4.4O2

10203040506070809050100O2concentration%Abscision%4.5Mineralnutrition

Anyoneofmineralnutritiondeficiencycausesincreaseinsenescenceandabscission.N、Zn——1AA，Ca——cellwall.

B——pollendevelopmentandpollentuberelongation.4.6Diseases，pests,radiationandotherstressescausesenescenceandabscission.Section5Controlofsenescence5.1Utilizationofgermplasmresistanttosenescenceselectionofvarietiesandcultivarsresisttosenescence。5.2