植物体内有机物运输和分配

Chaptersix:assimilatetransport,

distributionandsignaltransduction

(同化物运输、分配和信号转导)6.1systemofassimilatetransport(同化物运输系统)6.1.1shortdistancetransport(短距离运输)6.1.1.1胞内运输：细胞内和细胞器之间的物质运输。如光呼吸中CCP、PGA等在叶绿体、线粒体和过氧化酶体之间的运输。6.1.1.2胞间运输：包括质外体(阻力小)、共质体运输(阻力大且受胞间连丝的控制)，以及质外体与共质体间的运输。本文档共26页；当前第1页；编辑于星期日\16点41分BOX:transfercells(转移细胞)Therateatwhichmaterialcanbeactivelytransporteddependsonthenumberofmolecularpumpspresent,whichinturndependsonthesurfaceareaoftheplasmamembrane:Thelargerthemembrane,themoremolecularpumpsitcanhold.Incertainspecializedtransfercells,thewallsaresmoothontheoutersurfacebuthavenumerousfinger-likeandridgelikeoutgrowthsontheinnersurface.Theplasmamembraneispressedfirmlyagainstalltheconvolutionsandthushasamuchlargersurfaceareathanitwouldifthewallwereflat.Consequently,roomisavailableformanymolecularpumps,andhigh-volumetransportcanoccuracrossthesetransferwalls.Transfercellsarefoundinareaswhererapidshortdistancetransportisexpectedtooccur:inglandsthatsecretesalt,inareasthatpassnutrientstoembryos,andinregionswheresugarisloadedintooroutofphloem.本文档共26页；当前第2页；编辑于星期日\16点41分(a)Oncereleasedfromacell,amoleculediffusesinaseriesofrandomshortpathsasitcollideswithandbouncesoffothermolecules.Probabilityfavorsitsenteringaneighboringcell(molecules1,2,and3),butitcandiffuselaterallyalongthewallaswell(molecules4and5).(b)Inmanyglands,theapopIastislarge,somovementbetweencellsmaybefasterandeasierthanmovementwithincells.Suchglandsoftenhavealiningofcompacttissuethatisolatesthegland,preventingthesecretedmaterialfrompermeatingthewholeregion.本文档共26页；当前第3页；编辑于星期日\16点41分6.1.2longdistancetransport

(长距离运输)6.1.2.1pathway(途径)：phloem(韧皮部)。Girdlingexperiment(环割试验)、radioactivetracer(同位素示踪技术)及谚语“树怕扒皮”等可以证明，同化物运输的途径是维管组织的韧皮部。本文档共26页；当前第4页；编辑于星期日\16点41分水分和同化物运输的途径比较本文档共26页；当前第5页；编辑于星期日\16点41分Diagramshowingbasicelementsinthecirculationofwater,inorganicions,andassimilatesintheplant.Waterandinorganicionstakenupbytherootmoveupwardinthexyleminthetranspirationstream.Somemovelaterallyintotissuesoftherootandstem,whileothersaretransportedtogrowingplantpartsandmatureleaves.Intheleaves,substantialamountsofwaterandinorganicionsaretransferredtothephloemandareexportedwithsucroseintheassimilatestream.

本文档共26页；当前第6页；编辑于星期日\16点41分Asearlyastheseventeenthcentury,MarcelloMalpighiofItalynoticedthat,whenaringofbarkwasremovedfromastem(a),thetissuesabovetheringbecameswollen(b).Hecorrectlyinterpretedthisphenomenonasnewgrowthofwoodandbarktissuesstimulatedbyanaccumulationoffoodmovingdownfromtheleavesandinterceptedatthering.Malpighistudiedtheeffectofringingatdifferenttimesoftheyearandfoundthatnoswellingoccurredduringthewintermonths.Girdlingexperiment(环割试验)本文档共26页；当前第7页；编辑于星期日\16点41分14CO2示踪技术：TwoleafletsofabroadbeanplantwereenclosedinaPlexiglascontainerandexposed14CO2andlightfor35minutes.Duringthattime,14CO2wasincorporatedintosugars,whichwerethentransportedtootherpartsoftheplant.本文档共26页；当前第8页；编辑于星期日\16点41分6.1.2.2韧皮部组成由筛管(sievetube)、伴胞(companioncell)和薄壁细胞组成.筛管分子(sieveelement,SE)：除含有质膜、内质网、质体和线粒体，其它细胞器降解消失，具有韧皮蛋白(phloemprotein,P-蛋白)。筛管与伴胞形成筛管分子-伴胞复合体(sieveelement-companioncellcomplex,SE-CC)本文档共26页；当前第9页；编辑于星期日\16点41分(a)Longitudinal(radial)viewofsecondaryphloemofyew(Taxuscanadensis),showingverticallyorientedsievecells,strandsofparenchymacells,andfibers.Partsoftwohorizontallyorientedrayscanbeseentraversingtheverticalcells.(b)Detailofportionofthesecondaryphloemofyew,showingsieveareas,withcallose(stainedblue)onthewallsofthesievecells,andalbuminouscells.本文档共26页；当前第10页；编辑于星期日\16点41分6.1.2.3运输同化物的种类汁液干物质10～25%，多数为糖，其余为氨基酸(谷氨酸和天冬氨酸)、蛋白质、无机离子、有机离子和植物内源激素。利用蚜虫吻针法方法证明。本文档共26页；当前第11页；编辑于星期日\16点41分(a)Aphid(Longistigmacaryae)feedingonabasswood(Tiliaamericana,椴木)stem.Adropletof"honeydew"canbeseenemergingfromtheaphid.(b)Aphotomicrographshowingpartofthemodifiedmouthparts(stylets)oftheaphidinasievetubeofthesecondaryphloemofthebasswoodstem.Anarrowpointstothetipsofthestylers.本文档共26页；当前第12页；编辑于星期日\16点41分6.2韧皮部运输机理6.2.1运输方向：从源(source)到库(sink)。源是指产生或提供同化物的器官或组织，如功能叶、胚乳等；库是指消耗或积累同化物的器官或组织，如根、茎、果实、种子等。运输过程包括韧皮部装载、运输和韧皮部卸出三个部分Assimilatemovementissaidtofollowasource-to-sinkpattern.Theprincipalsourcesofassimilatesolutesarethephotosynthesizingleaves,butstoragetissuesmayalsoserveasimportantsources.Allplantpartsunabletomeettheirownnutritionalneedsmayactassinks,thatis,importersofassimilates.Thus,storagetissuesactassinkswhentheyareimportingassimilatesandassourceswhentheyareexportingassimilates.本文档共26页；当前第13页；编辑于星期日\16点41分6.2.2.1Concept(概念)：是指光合产物从叶肉细胞到筛管分子-伴胞复合体(sieveelement-companioncellcomplex)的整个过程。第一步：白天，叶肉细胞光合形成的磷酸三碳糖从叶绿体运到胞质溶胶；晚上，可能以葡萄糖状态离开叶绿体，转变为蔗糖(某些植物后来会将蔗糖转变为其他运输糖)。第二步：叶肉细胞的蔗糖运到叶片细脉的筛分子附近。第三步：筛分子装载，即糖分运入筛分子和伴胞。糖分和其他溶质从源运走的过程称为输出。6.2.2韧皮部装载(phloemloading)本文档共26页；当前第14页；编辑于星期日\16点41分质外体(apoplastic)和共质体(symplastic)同化物生产区同化物积累区同化物输出区质外体运输共质体运输6.2.2.2装载途径本文档共26页；当前第15页；编辑于星期日\16点41分6.2.2.3装载机理(限质外体)在筛分子或伴胞质膜中的ATP酶，不断地将H+泵到质外体(细胞壁)。质外体的H+浓度比共质体高，形成质子梯度作为推动力。通过ATP酶释放的能量，推动细胞内H+的输出和外界K+的输入，以维持膜内外的质子梯度。蔗糖与质子沿着这个梯度经过蔗糖-质子同向运输器(sucrose-protonsymporter)，一起进入筛分子-伴胞复合体。

本文档共26页；当前第16页；编辑于星期日\16点41分本文档共26页；当前第17页；编辑于星期日\16点41分6.2.3运输机理压力流动学说(pressureflowhypothesis)：源端(叶肉细胞)将蔗糖装载入SE-CC，接着木质部水分通过渗透作用也进入SE-CC，由此产生高的膨压。而在库端(如贮藏根)，当糖被卸出时，水分也离开韧皮部，于是膨压很低。源端和库端之间就存在膨压差，它推动筛管内容物的集流，穿过筛孔沿着系列筛分子向前运行，最终进入库细胞。

本文档共26页；当前第18页；编辑于星期日\16点41分本文档共26页；当前第19页；编辑于星期日\16点41分Sugarisactivelyloadedintothesievetubeatthesource.Withtheincreasedconcentrationofsugar,thewaterpotentialisdecreased,andwaterfromthexylementersthesievetubebyosmosis.Sugarisremoved(unloaded)atthesink,andthesugarconcentrationfalls;asaresult,thewaterpotentialisincreased,andwaterleavesthesievetube.Withthemovementofwaterintothesievetubeatthesourceandoutofitatthesink,thesugarmoleculesarecarriedpassivelybythewateralongtheconcentrationgradientbetweensourceandsink.本文档共26页；当前第20页；编辑于星期日\16点41分(a)Assucrose(s)isactivelytransportedintosieveelements,ΨsandΨcellbecomemorenegative,movingawayfromequilibriumwithcompanioncellsandotherneighboringcells.Watermovesintothesieveelements,squeezingphloemsapoutthroughthesievepores.Becausethesugarywaterescapesthroughsievepores,highpressuredoesnotbuildup,sothepressurepotentialdoesnotriseandstoptheinfluxofwater.Thewaterpotentialsofsieveelementsandsurroundingcellsneverreachequilibriumaslongassucroseisbeingpumped.Thesourceoftheglucosemaybephotosynthesisorthebreakdownofstarch.(b)Insinks,sucroseisactivelytransportedoutofsieveelements,andallprocessesworkinreversecomparedwithsources.Insomesinks,mostofthesucroseisconvertedtoglucoseandthenpolymerizedtostarch(storageorgans),isrespired(mosttissues),orisusedtoconstructnewcompounds(growingtissues).本文档共26页；当前第21页；编辑于星期日\16点41分BOX:P-proteinhypothesisP-protein,foundasafinenetworkadjacenttotheplasmamembraneinnersurfaceofuninjuredsieveelements.Whenphloemisruptured,thephloemsapinitiallysurgestowardthebreak;thisrapidmovementsweepstheP-proteinintothecellcenter,whereitbecomesatangledmass.Whenitiscarriedtoasieveareaorsieveplate,theP-proteinmassist