第十三章植物成花诱导-第二节光周期现象

第二周期现FlowerSwedishbotanistCarlvonLinnéobservedthatflowersopenandcloseatcertaintimesofday.In1745heproposedaflowerclocktocomplementthethenusedsundials.Itwouldindicatethetimewithanaccuracyofhalfanhour,evenwhenskyisovercast.ThisdialwaspaintedbyUrsulaSchleicher-Benzin1948.光周光光周期现5-methoxyN-植物对光周期的反Garner AllardMAMMOTHlocusarecessivegeneN.tabacumthatconfersshort-daybehavior(Allard,1919;Lang,1948).In1920,WightmanWellsGarnerandHenryArdellAllardwereworkingattheUSDA,inBeltsvilleontobacco[Nicotiana],whichnormallyflowersinthesummer.Theyalsonoticedthatsoybeanssownatdifferenttimesinthegreenhouseallfloweredatthesametime,regardlessofthedateofsowing.Attemptingtobreedtobacco,theywereworkingwithamutantnamed‘MarylandMammoth’,whichdidnotflowerinthesummer,butdidflowerinthewinter.Plantsgrewto12or15feetinheightbeforetheplantsflowered.Oneoftheirgoalswastopollinatethenormaltobaccousingpollenfromthe‘MarylandMammoth’,butthetimeintervaloffloweringbetweeneachplantwastoolongtoallowpollination.Theythereforesetouttoattempttoforcethe‘MarylandMammoth’toflowerduringthesummeratthesametimeasthenormaltobacco.‘MarylandMammoth’tobaccorequiresadaylengthof12hourorlessinordertoflower.ThelatitudeoftheU.S.D.A.inMarylandis y40oN.TobaccoseedsarenormallysowninthegreenhouseinFebandMarch,andtheseedlingsareplantedoutinthefieldduringAprilandMay,whenthetemperatureismilder.Whenplantedinthefieldthedaylengthisapproxima y14hr.Thisincreasesto15hrandthenonJune21,thedaylengthsbegintodecreaseduringthesummerandfall,finallyreachinga12hrdaylengthbySeptember21,whenfloweringisinitiated.Followingfloralinitiation,anumberofweeksarenecessaryforfloraldevelopmenttooccur.]Afterkee theplantsinagreenhouse,andadjustingtemperaturesunsuccessfully,theyformedahypothesisthatstatedthatitwasthelengthofdaywhichcontrolledflowering.Itwasdifficulttounderstandthatfloweringwasactuallypromotedbygivinglesslight,aconditionwhichingeneralpreventedflowering.Theybuiltalight-tighttentaroundthe‘MarylandMammoth’,whichtheyputupeachdayat5:00pmandtookdownat9:00amea orning,givingonlyan8-hourdaylength.Itworked…andthe‘MarylandMammoth’tobaccowasforcedintoflowering.ThisworklaidthefoundationofanenormousamountofresearchdealingwiththePhotoperiodicResponsesofPlants.ThousandsofpapershavebeenpublisheddealingwithPhotoperiodism.Butinall,wehavenoswee generalities.Eachspecies,andevenvarieties,seemstohaveitsownfeaturesof长日植物（long-day 如典型的长日植物天仙子必须满足一定天数的11.5小时日照才能开花，如果日照长度短于8.511.5小时就不能开SpinachlongdayplantLongDay短日植物（short-day指在24小时昼夜周期照长度短于一定时数才对这些植物适当延长或缩短光照可促进和提早苏、、黄麻、草莓、烟草、菊花、秋海棠、腊梅、牵牛等。Poinsettiashortday一品ShortDay日中性植物（day-neutralplant，缩写为DNP）DayNeutralBuckwheat普通荞DayNeutral 照植物（intermediate-daylengthplant）长－短日植物（long-shortdayplant）这类植物短－长日植物（short-longdayplant）这类植物 周期植物（amphophotoperiodismplant） 临界日长要求的相对性和绝对长日植物与短日植物的相对临界日长与植物品种、温度等的关光期与暗期的作Cocklebur（苍耳）Xanthium典型的短日植HamnerandBonnerinthelate光周期的感受部光周期诱导与开花素光周期诱导与光敏光周期诱导与生物光周期诱导的分子机M.Kh.感受部开花 FourExamplesfromtheCrassulaceaeinWhichFloweringIsInducedinaNoninducedScionbyTransmissionofFlorigenfromaFlorallyInducedStock.Ineachcase,thestock(belowthegraftunion)isthedonor,andthescion(abovethegraftunion)isthereceptor.Arrowspointtowardtheunions.Ineachcase,theappropriatephotoperiodicconditionswereusedtoinducefloweringofthedonorwhereasthereceptorwasanoninductivephotoperiod.Noneofthecontrolgraftswithnoninduceddonorscausedfloweringinthe(datanotTheSDPKalanchoe¨blossfeldianaasdonorfortheLDPSedumspectabileasreceptor(Zeevaart,TheLDPS.spectabileasdonorfortheSLDPEcheveriaharmsii(myTheLSDPBryophyllumcrenatumdonorfortheLDPS.spectabile(myunpublisheddata).TheLSDPB.daigremontianumasfortheSLDPE.(Zeevaart,Graft-transmissionofSFT(SINGLE-FLOWERTRUSS)signalfromtomatotopromotefloweringinMarylandMammothtobacco(Lifschitzetal.2006).(a)AMarylandMammothplantgrownunderlong(18-hlight/6-hdark)days,whichdidnotflower.(b)Earlyfloweringinlong-daygrownMarylandMammothplantsexpressingthe35S:SFTtransgene.(c)Tomato35S:SFTdonorscionsgraftedontoleafpetioles(boxed)ofaMarylandMammothreceiverinducedfloweringinthetobaccoreceiver(arrow)grownunderlong-dayconditions.Thephotographswerereproducedfrom(Lifschitzetal.2006).PhytochromeistheprimaryphotoreceptorinBlue-lightreceptorsalsoregulatecry2mutantsflowermuchlaterthanwildtypeduringlongbutnotshortdaysModelsforthemechanismofphotoperiodicThecoincidence耦合模Intheexternalcoincidencemodel,responsesmaybetriggeredwhenlightcoincideswithaphotoinduciblephase.Thisphotoinduciblephasemaybedeterminedbythediurnalpatternofexpressionofaregulatorymolecule,representedbythesolidwavyline.Expressionofthismoleculeisexpectedtoberestrictedtothedarkperiodundershortdays,buttocoincidewithlightunderlong-dayconditions(arrows).(B)Intheinternalcoincidencemodel,theeffectofphotoperiodistoalterthephaseanglebetweentwoendogenousrhythms(representedbythesolidanddottedlines).Oscillationsinthelevelsoftworegulatorymoleculesthatrequireeachotherforactivitymayallowaresponsewhenbroughtintocoincidence,underlong-dayconditions,forexample.Whiteandblackboxesatthetopofthediagramsrepresentperiodsoflightanddarkness,MODELFORAFEEDBACKLOOPINVOLVINGLHY,CCA1,ANDPHYandCRYasLHY,CCA1andTOC1negativefeedbackLHY,CCA1repressexpressionofTOC1,theirpositiveGenerationofcircadianrhythms,includingthatofCOforfloweringtimeELF3gatesthelightsignals,resettingitatsinceitselfaCCG,thisallowscyclingevenatconstantZLPandGIalsoactonlightMolecularinteractionsthatshapetheplantcircadianLHCBandothermorninggenes↑

TOC1ELF4CCA1 TOC1ELF4ReleaseofinhibitionofTOC1,

ActivateexpressionCCA1,RepressTOC1,CCA1 TOC1ELF4=>zincfingertranscription=>promotesfloweringunder=>stimulatesexpressionof(FLOWERINGLOCUSandEnd-Of-VOL309SEPTEMBERLeaf-specificheatshockactivationofgeneexpression.GUSstaininginwholeplants(AtoC)andshootapex(DtoF)ofHsp:GUSplantsgrownundershort-dayconditions.Integrationofsignalstogenerateaflower.AppropriatedaylengthallowstheaccumulationofthetranscriptionfactorCOthatcontrolsexpressionofFTintheleaf.(Inset)FTtranscriptmovesthroughthephloemtotheshootapexwheretheFTproteinisproducedandinteractswiththetranscriptionfactorFD.ThecomplexthenactivateskeygenessuchasAP1tostartflowerdevelopment.LEAFY(LFY)isatranscriptionfactorrequiredforAP1expressioninwild-typeplants.LFYexpressionisup-regulatedbyFTintheshootapex.AcurrentmodeloftheactionoftheFTflorigen.(A)Vegetativephase.Intheabsenceofproperlightsignalsoratveryyoungseedlingstage,FTexpressionisabsent.TFL1proteinistranslatedintheinnercellsand esevenlydistributedacrosstheSAM(shownasblueshading).TFL1proteininteractswithabZIPtranscriptionfactorFDandpreventsFDfromactivating genesforflowering.(B)Floraltransition.TranscriptionofFTisinducedinthephloemcompanioncellsintheleaf(shownaspinklinesaroundphloemrepresentedbyawhi ine)inresponsetolightsignalsviaactionofCOprotein.FTproteinistranslatedandistransportedtotheshootapexwhereitinteractswithabZIPtranscriptionfactorFDbycompetingagainstTFL1protein(shownasblueshading).TheFT–FDcomplex localizedinthenucleusandactivatestranscriptionof genessuchasafloralmeristemidentitygene,AP1(shownasyellowshading).AP1,inturn,specifiedthefloralfateofnascentlateralmeristemstoinitiatefloralmorphogenesis.FTproteindoesnotpromoteitsowntranscription(agraybrokenarrowwithan‘X’onit)butmayactintranstofacilitateitsmovement(ablackbrokenarrowwithaquestionmark).Seetextfordetails.Hd3aprotein,whichisthefloweringhormoneofthericeplant,isproducedinthefibrovascularbundleoftheleavesandthentransportedtothemeristematthetipofthestem,whereitcausesflowerstoform.(©NARAInstituteofScienceandTechnology)Thecoincidence

AphysiologicalmodelofAconservedflowering-timepathwayinriceandArabidopsisconferstheoppositeeffecttodaylengthTheCoincidenceModelofHHd1Hd1=Heading-date1,riceorthologofCOHd3a=Heading-date3a,riceorthologofFTComparisonofthefunctionoforthologsCOandHd1,FTandHd3aKobayashiandWeigel2007GenesDev21:2371-Amodelforthephotoperiodiccontroloffloweringinrice.UnderSDconditions,Hd1andEhd1positivelyregulateHd3aandpromotefloweringintheactivationpathway