植物生理學(xué)：植物衰老與器官脫落

PlantSenescenceandOrganAbscission

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(球莖)andbulb（鱗莖）——lily。InsummerInwinter(3)DeciduoussenescenceTheleaffallsinspeciousseason,insummerorwinter.Deciduoustrees(4)ProgressivesenescenceSenescenceonlyoccursinolderorganortissue.Neworganortissuedevelopswhileoldonesaresenescing.Greentrees。衰老有其積極的生物學(xué)意義，不僅能使植物適應(yīng)不良環(huán)境條件，而且對(duì)物種進(jìn)化起重要作用。溫帶落葉樹的葉片，在冬前全樹葉片脫落，從而降低蒸騰作用，有利于安全越冬。通常植物在衰老時(shí)，其營(yíng)養(yǎng)器官中的物質(zhì)降解、撤退并再分配到種子、塊莖和球莖等新生器官中去。如花的衰老及其衰老部分的養(yǎng)分撤離，能使受精胚珠正常發(fā)育；果實(shí)成熟衰老使得種子充實(shí)，有利于繁衍后代。1.2ProgramforplantsenescenceSenescencecanoccuratdifferentlevels:cell,tissue,organsandwholeplant.1.2.1Cellsenescence

Membraneandorganellesenescence。1.2.1.1、Senescenceincellmembrane。(1)Lipidphasechange。Biomembranechangesitsphasefromliquid-crystallinestatetosolid-gelstate.

Hardandinextensive，fluiditydecreasesandcohesionincreases。液晶相凝固相衰老、低溫六方晶相I六方晶相II混合相衰老生物膜幾種相變示圖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組織中。CH2—O—C—R1CHCH2—O—P—O-XR2—C—OOOOOHA1A2BCDThedehydrationboundfordifferentphospholipases磷脂的降解磷脂游離多元不飽和脂肪酸磷脂酶脂氧合酶不飽和脂肪酸的氫過氧化物脂氧合酶自由基分解醛類（如丙二醛）和易揮發(fā)的烴類（乙烯，乙烷，戊烷）等脂氧合酶亞麻酸茉莉酸（JA）JA是一種促進(jìn)植物衰老的內(nèi)源物質(zhì)，有人稱為死亡激素。Phospholipid

↓phospholipaseAorBPolydouble-boundfatacid

↓Lox(lipoxygenase)OrganicfreeradicalsR’HC=CCH2C=CR’’-COOHHHH順，順—甲叉間二烯R’HC=CCHC=CR’’-COOHHHH?O2OOH?奪取氫，形成過氧自由基R’HC=CCHC=CR’’-COOHHHH?自由基：反，順—共軛二烯重排OOH?R’HC=CCHC=CR’’-COOHHHHOOH過氧化作用反，順—共軛二烯過氧化物（4）Biomembranedegradationandleakage.Lossequilibriumofionsanddisorderofmetabolism。1.2.1.2、Organellesenescence。

RibosomeandroughER↓→chloroplastsbreakdown→mitochondriacristaeswollen↑→vacuolebroken.Autophagyoccursandcellsenescesanddegrades.1.2.2Programmedcelldeath(PCD，程序性細(xì)胞死亡)Theorganismcontrolstheinitiationandexecutionofthecelldeathprocess,thesetypesofcelldeatharereferredtoasprogrammedcelldeath(PCD)PCD可發(fā)生在植物的各種細(xì)胞。過程：DNA斷裂、染色質(zhì)固縮、胞泡形成、凋亡小體形成。動(dòng)物細(xì)胞PCD后產(chǎn)物被其他細(xì)胞吞噬利用，植物細(xì)胞PCD后產(chǎn)物用于本身細(xì)胞次生壁的構(gòu)成。OneoftheimportantfunctionsofPCDinplantsisprotectionagainstpathogens.Whenapathogeninfectsaplant,cellsatthesiteoftheinfectionquicklyaccumulatehighconcentrationsoftoxicphenoliccompoundsanddie.Thedeadcellsformasmallcircularislandcalledanecroticlesion,whichisolatesandpreventstheinfectionfromspreadingtosurroundinghealthytissues.Thisrapidandlocaizeddeathduetopathogenattackiscalledthehypersensitiveresponse,whichisageneticallyprogrammedprocess.PCD發(fā)生過程啟動(dòng)階段（initiationstage)啟動(dòng)細(xì)胞死亡信號(hào)的產(chǎn)生和傳遞效應(yīng)階段(effectorstage)caspase的活化和線粒體通透性的改變。Caspase屬于半胱氨酸蛋白酶家族，直接導(dǎo)致PCD細(xì)胞原生質(zhì)解體.Caspase全稱為含半胱氨酸的天冬氨酸蛋白水解酶(cysteinylaspartatespecificproteinase)。caspase是一組存在于細(xì)胞質(zhì)中具有類似結(jié)構(gòu)的蛋白酶。Caspase與真核細(xì)胞凋亡密切相關(guān)，并參與細(xì)胞的生長(zhǎng)、分化與凋亡調(diào)節(jié)。它們的活性位點(diǎn)均包含半胱氨酸殘基,能特異性的切割靶蛋白的天冬氨酸殘基上的肽鍵.酶解清除階段(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(自體吞噬)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

1.2.3.1Leafsenescence。（1）Photosynthesisdeclines-----slowerphaseandfasterphase。Decreaseinactivityandcontentofphotosynthetickeyenzyme(Rubisco)Decreaseinactivityofphotoelectrontransportandphotophosphorylation.Decreaseinstomatalconductance.Decreaseinchlorophyll.Leafyellow.Organelledegradation:葉綠體內(nèi)基?！ㄖ愋◇w）→內(nèi)質(zhì)網(wǎng)→核糖體→線粒體→液泡膜。（二）器官衰老1.葉片衰老2.花器官的衰老葉色-----由綠變黃根據(jù)葉色將葉片衰老分為五級(jí)花冠---雄蕊---雌蕊

花器官3.根系的衰老果實(shí)成熟意味衰老開始根系是邊生長(zhǎng)邊衰老，根毛壽命很短相對(duì)值大小呼吸速率可溶性氮化物蛋白質(zhì)葉綠素含量光化學(xué)活性光合速率Rubisco活力天葉片衰老期間的生理變化示意圖脂質(zhì)小體Fig20.13Impactofsenescenceonplastidultrastructureinleavesofwild-typeandastay-greenmutantoftheC3grassX.Festulolium.(A)Priortosenescence,thechloroplastsofawild-typeandmutantplantscontainnumerousgrana,stacksofappressedthylakoidmembranes.(B)Theseinternalmembranestructuresarelostduringsenescenceofawild-typemesophyllcell,andelectron-denselipiddropletsknownasplastoglobuliaccumulate.(C)Retentionofintrinsicthylakoidmembraneproteins,pigments,andotherhydrophobiccomponentsgivesthegerontoplasts(老年質(zhì)體)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

1.2.3.2Seedaging。Theviabilityofseedlossinverselyfrommaturetodeath。Degradationandleakageofbiomembrane:MitochondriaandERbecomeswollen,plasmicmembranecontactsanddepartfromcellwall.DNAinjury，broken。Enzymeactivitydecreases:dehydrase。Storagematterexhausting,freefatacidrising.

1.2.4Senescenceinwholeplant：Onesettingplants:一生中只開一次花的植物-全部一年生\二年生和某些多年生的植物.Polysettingplants------graduallysenescing一生中多次開花結(jié)實(shí)的植物-木本植物\多年生宿根性草本植物.Section2SenescenceMechanismandregulation2.1

Senescencecausedbynutritionexhaustion

Nutritionexhaustion

theory：Senescencecausedbyreproductiveorgan.Suchastomato,ifsetting,survivesforoneseason,ifflowerremovedoff,survivesforseveralyear.Roottissueculture,morethan30years.龍舌蘭doesnotflower,liveforseveraldecades,andfloweringalive—8-10years。Oppositeviews:Sunflowersenescespriortoflowerinitiation.Removingfloweracceleratessenescenceinmaizeandpopper自由基損傷學(xué)說：自由基有細(xì)胞殺手之稱。1955年哈曼（Harman）就提出，衰老過程是細(xì)胞和組織中不斷進(jìn)行著的自由基損傷反應(yīng)的總和。

三、植物衰老的機(jī)理與調(diào)節(jié)（一）植物衰老的機(jī)理1.營(yíng)養(yǎng)虧缺學(xué)說

許多一年生植物在開花結(jié)實(shí)后，營(yíng)養(yǎng)體衰老、凋萎、枯死。原因主要是營(yíng)養(yǎng)物質(zhì)的征調(diào)和同化物的再分配與再利用。即將營(yíng)養(yǎng)體內(nèi)的物質(zhì)大量運(yùn)輸?shù)缴称鞴?，促進(jìn)營(yíng)養(yǎng)體衰老。摘除果實(shí)可以延緩衰老。存在問題：

1）供給已開花結(jié)實(shí)植株充分養(yǎng)料，無法免除其衰老

2）雌雄異株開花后并未結(jié)實(shí)，雄株仍然死亡。如菠菜和大麻

2.DNA損傷學(xué)說差誤理論要點(diǎn)：植物衰老是由于分子基因器在蛋白質(zhì)合成過程中引起差誤積累所造成的。當(dāng)錯(cuò)誤的產(chǎn)生超過某一閾值時(shí)，機(jī)能失常，出現(xiàn)衰老、死亡。這種差誤由于DNA的裂痕或缺損導(dǎo)致錯(cuò)誤轉(zhuǎn)錄、翻譯，錯(cuò)誤可能在蛋白質(zhì)合成軌道一處或幾處出現(xiàn)。這種錯(cuò)誤可能是氨基酸排列錯(cuò)誤，或者是多肽鏈折疊錯(cuò)誤。錯(cuò)誤的發(fā)生導(dǎo)致無功能的蛋白質(zhì)（酶）的積累。3.遺傳程序?qū)W植物衰老、死亡是由其自身基因程序所決定的。一切衰老過程都是基因控制。牽牛花的衰老很快，在開花當(dāng)天即衰老，第二天脫落細(xì)胞程序性死亡（programedcelldeath）：植物體內(nèi)存在特定基因控制細(xì)胞衰老事件。---DNA降解為特征外源乙烯--誘導(dǎo)WT擬南芥衰老對(duì)乙烯不敏感型突變體無影響生命衰老受遺傳控制4.生物自由基損傷學(xué)說

衰老常伴有超氧化物歧化酶（superoxidedismutase，SOD）活性降低和脂氧合酶活性升高（lipoxygenase，LOX，催化膜脂中不飽和脂肪酸的加氧，產(chǎn)生自由基），導(dǎo)致生物體內(nèi)自由基產(chǎn)生與消除的平衡被破壞，以致積累過量的自由基，對(duì)細(xì)胞膜及生物大分子產(chǎn)生破壞作用。如加強(qiáng)酶蛋白的降解、促進(jìn)脂質(zhì)過氧化反應(yīng)、加速乙烯的產(chǎn)生、引起DNA的損傷、改變酶的性質(zhì)等，進(jìn)而引起衰老（1）生物自由基（FreeRadical）的概念

生物自由基（FreeRadical）是指生物體代謝產(chǎn)生的自由基。又稱游離基，是帶有未配對(duì)電子的原子、原子團(tuán)、分子或離子等。（2）生物自由基種類生物自由基

氧自由基（oxygenfreeradical）（主要的生物自由基）非含氧自由基，如CH3.、（C6H5）3C無機(jī)氧自由基，如超氧自由基（O2.-）、羥基自由基（.OH）；有機(jī)氧自由基，如過氧化物自由基（ROO.）、烷氧自由基（RO.）和多元不飽和脂肪酸自由基（PUFA.）。含氧非自由基(1O2,H2O2)活性氧自由基的特點(diǎn)：不穩(wěn)定，壽命短；化學(xué)性質(zhì)活潑，氧化能力強(qiáng)；能持續(xù)進(jìn)行鏈?zhǔn)椒磻?yīng)。

活性氧（activeoxygen）化學(xué)性質(zhì)活潑，氧化能力很強(qiáng)的含氧物質(zhì)的總稱。生物體內(nèi)活性氧

--氧自由基、單線態(tài)氧和H2O2、NO、NO2等。它們能氧化生物大分子，破壞細(xì)胞膜的結(jié)構(gòu)與功能，其中O2.-的氧化能力特強(qiáng)，能迅速攻擊所有生物大分子，包括DNA，引起細(xì)胞死亡。（3）自由基的產(chǎn)生產(chǎn)生部位：細(xì)胞壁、細(xì)胞核、葉綠體、線粒體及微體等。產(chǎn)生途徑：?jiǎn)坞娮拥难趸€原；共價(jià)鍵的斷裂；高能輻射；光分解；逆境條件A.單線態(tài)氧（1O2）的產(chǎn)生B.超氧自由基的產(chǎn)生C.羥基自由基的產(chǎn)生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。對(duì)蛋白質(zhì)的傷害:由脂質(zhì)過氧化過程所產(chǎn)生的脂性自由基（如RO.、ROO.）能引發(fā)膜蛋白（包括膜酶）發(fā)生聚合和交聯(lián),是自由基對(duì)蛋白質(zhì)損傷的主要形式。丙二醛對(duì)蛋白質(zhì)的交聯(lián)作用。

脂質(zhì)過氧化的最終產(chǎn)物丙二醛（MAD）能與蛋白質(zhì)等生物大分子產(chǎn)生交聯(lián)反應(yīng)。

由丙二醛引發(fā)的這種交聯(lián)反應(yīng)既可在蛋白質(zhì)分子內(nèi)進(jìn)行，也可在蛋白質(zhì)分子間進(jìn)行。

丙二醛與兩個(gè)蛋白質(zhì)分子交聯(lián)形成的物質(zhì)叫脂褐素（LPF）。5.激素平衡學(xué)說

植物體內(nèi)各種植物激素相對(duì)水平的不平衡是引起衰老的原因。抑制衰老的激素（如CTK、IAA、GA）與促進(jìn)衰老的激素（ETH、ABA）之間可相互作用、協(xié)同調(diào)控衰老過程。

茉莉酸（jasmonicacid,JA）茉莉酸甲脂（methyljasmonate,MJ）死亡激素

不僅抑制植物生長(zhǎng),且能促進(jìn)植物衰老。加快葉片中葉綠素降解,提高蛋白酶和核糖核酸酶類活性,加速生物大分子的降解。它促進(jìn)植物衰老的作用比ABA還強(qiáng)ABA和ETH----植物衰老激素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.

2.2.5.1feedradical

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-+O2OHisthemostpoisonfreeradicalinthelivingthings2.2.5.2Freeradicalscavengingsystemsinplant(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.第五節(jié)器官脫落的生理一、器官脫落的概念植物器官自然離開母體的現(xiàn)象稱為脫落（abscission）。三種類型正常脫落：衰老或成熟引起的脫落---種子和果實(shí)。脅迫脫落：因環(huán)境條件脅迫和生物因素引起的脫落。生理脫落：因植物本身生理活動(dòng)而引起的脫落。二、器官脫落的機(jī)理（一）離層與脫落

葉片脫落之前，離層細(xì)胞衰退，果膠酶與纖維素酶活性增強(qiáng)，中層分解，葉片脫落。（二）激素與脫落1.IAA脫落的生長(zhǎng)素梯度學(xué)說(Addiccott,1955)：器官的脫落與離層兩端IAA的濃度梯度有關(guān)。當(dāng)遠(yuǎn)軸端/近軸端IAA比值低時(shí)，加速離層的形成，促進(jìn)脫落。當(dāng)遠(yuǎn)軸端/近軸端IAA比值高時(shí)，抑制或延緩離層形成，抑制脫落；2.ETH

誘導(dǎo)果膠酶和纖維素酶合成，提高酶活性，促進(jìn)離層分解，加速脫落。3.ABA

促進(jìn)脫落機(jī)理---可能與其抑制葉柄內(nèi)IAA的傳導(dǎo)和促進(jìn)分解細(xì)胞壁酶類的分泌有關(guān)。（三）營(yíng)養(yǎng)與脫落

碳水化合物和蛋白質(zhì)等有機(jī)營(yíng)養(yǎng)不足是花果脫落的主要原因之一。三、影響器官脫落的環(huán)境因素1.光照強(qiáng)光抑制脫落弱光促進(jìn)脫落

長(zhǎng)日照抑制脫落短日照促進(jìn)脫落光強(qiáng)光質(zhì)2.水分

干旱提高IAA氧化酶的活性，降低CTK含量，提高ETH和ABA含量，促進(jìn)脫落。水淹時(shí)，也會(huì)出現(xiàn)落花，落果，落葉3.溫度高溫、低溫均促進(jìn)脫落。4.O2高O2、低O2都促進(jìn)ETH的合成。高O2還導(dǎo)致呼吸的加強(qiáng)，光合產(chǎn)物消耗加大，導(dǎo)致脫落。5.礦質(zhì)營(yíng)養(yǎng)缺乏N、Zn、Ca能導(dǎo)致脫落。6.其他因素大氣污染，病蟲害，鹽害等Budincottonis70％abscission，flowersorfruitsinsoybeanis60-70%abscission。3.1Abscissioninanatomyandphysiology3.1.1Abscissioninanatomy

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

Cellulaseactivityincreasesinbean,cottonandcitrusduringleafabscission。

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

WhenIAAisappliedinthepartoutsideofabscission(遠(yuǎn)基（軸）端),abscissionpromotes,inotherway,WhenIAAisappliedinthepartinsideofabscission(近基（軸）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.三、脫落的調(diào)控1．防止脫落----

園藝作物（蔬菜）

2,4-D---防止茄果類植物落花，如茄子、番茄等

NAA---防止落果（缺點(diǎn)--提前呼吸躍變，不耐貯藏）低濃度2,4-D,NAA-----減少棉花早期幼鈴脫落

GA-----能增加棉花座鈴。

CCC、B9、PP333等，對(duì)防止落鈴也有明顯效果。