植物體內(nèi)有機(jī)物運(yùn)輸和分配

Chaptersix:assimilatetransport,

distributionandsignaltransduction

(同化物運(yùn)輸、分配和信號轉(zhuǎn)導(dǎo))6.1systemofassimilatetransport(同化物運(yùn)輸系統(tǒng))6.1.1shortdistancetransport(短距離運(yùn)輸)胞內(nèi)運(yùn)輸：細(xì)胞內(nèi)和細(xì)胞器之間的物質(zhì)運(yùn)輸。如光呼吸中CCP、PGA等在葉綠體、線粒體和過氧化酶體之間的運(yùn)輸。胞間運(yùn)輸：包括質(zhì)外體(阻力小)、共質(zhì)體運(yùn)輸(阻力大且受胞間連絲的控制)，以及質(zhì)外體與共質(zhì)體間的運(yùn)輸。目前一頁\總數(shù)二十六頁\編于十四點(diǎn)BOX:transfercells(轉(zhuǎn)移細(xì)胞)Therateatwhichmaterialcanbeactivelytransporteddependsonthenumberofmolecularpumpspresent,whichinturndependsonthesurfaceareaoftheplasmamembrane:Thelargerthemembrane,themoremolecularpumpsitcanhold.Incertainspecializedtransfercells,thewallsaresmoothontheoutersurfacebuthavenumerousfinger-likeandridgelikeoutgrowthsontheinnersurface.Theplasmamembraneispressedfirmlyagainstalltheconvolutionsandthushasamuchlargersurfaceareathanitwouldifthewallwereflat.Consequently,roomisavailableformanymolecularpumps,andhigh-volumetransportcanoccuracrossthesetransferwalls.Transfercellsarefoundinareaswhererapidshortdistancetransportisexpectedtooccur:inglandsthatsecretesalt,inareasthatpassnutrientstoembryos,andinregionswheresugarisloadedintooroutofphloem.目前二頁\總數(shù)二十六頁\編于十四點(diǎn)(a)Oncereleasedfromacell,amoleculediffusesinaseriesofrandomshortpathsasitcollideswithandbouncesoffothermolecules.Probabilityfavorsitsenteringaneighboringcell(molecules1,2,and3),butitcandiffuselaterallyalongthewallaswell(molecules4and5).(b)Inmanyglands,theapopIastislarge,somovementbetweencellsmaybefasterandeasierthanmovementwithincells.Suchglandsoftenhavealiningofcompacttissuethatisolatesthegland,preventingthesecretedmaterialfrompermeatingthewholeregion.目前三頁\總數(shù)二十六頁\編于十四點(diǎn)6.1.2longdistancetransport

(長距離運(yùn)輸)pathway(途徑)：phloem(韌皮部)。Girdlingexperiment(環(huán)割試驗(yàn))、radioactivetracer(同位素示蹤技術(shù))及諺語“樹怕扒皮”等可以證明，同化物運(yùn)輸?shù)耐緩绞蔷S管組織的韌皮部。目前四頁\總數(shù)二十六頁\編于十四點(diǎn)水分和同化物運(yùn)輸?shù)耐緩奖容^目前五頁\總數(shù)二十六頁\編于十四點(diǎn)Diagramshowingbasicelementsinthecirculationofwater,inorganicions,andassimilatesintheplant.Waterandinorganicionstakenupbytherootmoveupwardinthexyleminthetranspirationstream.Somemovelaterallyintotissuesoftherootandstem,whileothersaretransportedtogrowingplantpartsandmatureleaves.Intheleaves,substantialamountsofwaterandinorganicionsaretransferredtothephloemandareexportedwithsucroseintheassimilatestream.

目前六頁\總數(shù)二十六頁\編于十四點(diǎn)Asearlyastheseventeenthcentury,MarcelloMalpighiofItalynoticedthat,whenaringofbarkwasremovedfromastem(a),thetissuesabovetheringbecameswollen(b).Hecorrectlyinterpretedthisphenomenonasnewgrowthofwoodandbarktissuesstimulatedbyanaccumulationoffoodmovingdownfromtheleavesandinterceptedatthering.Malpighistudiedtheeffectofringingatdifferenttimesoftheyearandfoundthatnoswellingoccurredduringthewintermonths.Girdlingexperiment(環(huán)割試驗(yàn))目前七頁\總數(shù)二十六頁\編于十四點(diǎn)14CO2示蹤技術(shù)：TwoleafletsofabroadbeanplantwereenclosedinaPlexiglascontainerandexposed14CO2andlightfor35minutes.Duringthattime,14CO2wasincorporatedintosugars,whichwerethentransportedtootherpartsoftheplant.目前八頁\總數(shù)二十六頁\編于十四點(diǎn)韌皮部組成由篩管(sievetube)、伴胞(companioncell)和薄壁細(xì)胞組成.篩管分子(sieveelement,SE)：除含有質(zhì)膜、內(nèi)質(zhì)網(wǎng)、質(zhì)體和線粒體，其它細(xì)胞器降解消失，具有韌皮蛋白(phloemprotein,P-蛋白)。篩管與伴胞形成篩管分子-伴胞復(fù)合體(sieveelement-companioncellcomplex,SE-CC)目前九頁\總數(shù)二十六頁\編于十四點(diǎn)(a)Longitudinal(radial)viewofsecondaryphloemofyew(Taxuscanadensis),showingverticallyorientedsievecells,strandsofparenchymacells,andfibers.Partsoftwohorizontallyorientedrayscanbeseentraversingtheverticalcells.(b)Detailofportionofthesecondaryphloemofyew,showingsieveareas,withcallose(stainedblue)onthewallsofthesievecells,andalbuminouscells.目前十頁\總數(shù)二十六頁\編于十四點(diǎn)運(yùn)輸同化物的種類汁液干物質(zhì)10～25%，多數(shù)為糖，其余為氨基酸(谷氨酸和天冬氨酸)、蛋白質(zhì)、無機(jī)離子、有機(jī)離子和植物內(nèi)源激素。利用蚜蟲吻針法方法證明。目前十一頁\總數(shù)二十六頁\編于十四點(diǎn)(a)Aphid(Longistigmacaryae)feedingonabasswood(Tiliaamericana,椴木)stem.Adropletof"honeydew"canbeseenemergingfromtheaphid.(b)Aphotomicrographshowingpartofthemodifiedmouthparts(stylets)oftheaphidinasievetubeofthesecondaryphloemofthebasswoodstem.Anarrowpointstothetipsofthestylers.目前十二頁\總數(shù)二十六頁\編于十四點(diǎn)6.2韌皮部運(yùn)輸機(jī)理6.2.1運(yùn)輸方向：從源(source)到庫(sink)。源是指產(chǎn)生或提供同化物的器官或組織，如功能葉、胚乳等；庫是指消耗或積累同化物的器官或組織，如根、莖、果實(shí)、種子等。運(yùn)輸過程包括韌皮部裝載、運(yùn)輸和韌皮部卸出三個部分Assimilatemovementissaidtofollowasource-to-sinkpattern.Theprincipalsourcesofassimilatesolutesarethephotosynthesizingleaves,butstoragetissuesmayalsoserveasimportantsources.Allplantpartsunabletomeettheirownnutritionalneedsmayactassinks,thatis,importersofassimilates.Thus,storagetissuesactassinkswhentheyareimportingassimilatesandassourceswhentheyareexportingassimilates.目前十三頁\總數(shù)二十六頁\編于十四點(diǎn)Concept(概念)：是指光合產(chǎn)物從葉肉細(xì)胞到篩管分子-伴胞復(fù)合體(sieveelement-companioncellcomplex)的整個過程。第一步：白天，葉肉細(xì)胞光合形成的磷酸三碳糖從葉綠體運(yùn)到胞質(zhì)溶膠；晚上，可能以葡萄糖狀態(tài)離開葉綠體，轉(zhuǎn)變?yōu)檎崽?某些植物后來會將蔗糖轉(zhuǎn)變?yōu)槠渌\(yùn)輸糖)。第二步：葉肉細(xì)胞的蔗糖運(yùn)到葉片細(xì)脈的篩分子附近。第三步：篩分子裝載，即糖分運(yùn)入篩分子和伴胞。糖分和其他溶質(zhì)從源運(yùn)走的過程稱為輸出。6.2.2韌皮部裝載(phloemloading)目前十四頁\總數(shù)二十六頁\編于十四點(diǎn)質(zhì)外體(apoplastic)和共質(zhì)體(symplastic)同化物生產(chǎn)區(qū)同化物積累區(qū)同化物輸出區(qū)質(zhì)外體運(yùn)輸共質(zhì)體運(yùn)輸裝載途徑目前十五頁\總數(shù)二十六頁\編于十四點(diǎn)裝載機(jī)理(限質(zhì)外體)在篩分子或伴胞質(zhì)膜中的ATP酶，不斷地將H+泵到質(zhì)外體(細(xì)胞壁)。質(zhì)外體的H+濃度比共質(zhì)體高，形成質(zhì)子梯度作為推動力。通過ATP酶釋放的能量，推動細(xì)胞內(nèi)H+的輸出和外界K+的輸入，以維持膜內(nèi)外的質(zhì)子梯度。蔗糖與質(zhì)子沿著這個梯度經(jīng)過蔗糖-質(zhì)子同向運(yùn)輸器(sucrose-protonsymporter)，一起進(jìn)入篩分子-伴胞復(fù)合體。

目前十六頁\總數(shù)二十六頁\編于十四點(diǎn)目前十七頁\總數(shù)二十六頁\編于十四點(diǎn)6.2.3運(yùn)輸機(jī)理壓力流動學(xué)說(pressureflowhypothesis)：源端(葉肉細(xì)胞)將蔗糖裝載入SE-CC，接著木質(zhì)部水分通過滲透作用也進(jìn)入SE-CC，由此產(chǎn)生高的膨壓。而在庫端(如貯藏根)，當(dāng)糖被卸出時，水分也離開韌皮部，于是膨壓很低。源端和庫端之間就存在膨壓差，它推動篩管內(nèi)容物的集流，穿過篩孔沿著系列篩分子向前運(yùn)行，最終進(jìn)入庫細(xì)胞。

目前十八頁\總數(shù)二十六頁\編于十四點(diǎn)目前十九頁\總數(shù)二十六頁\編于十四點(diǎn)Sugarisactivelyloadedintothesievetubeatthesource.Withtheincreasedconcentrationofsugar,thewaterpotentialisdecreased,andwaterfromthexylementersthesievetubebyosmosis.Sugarisremoved(unloaded)atthesink,andthesugarconcentrationfalls;asaresult,thewaterpotentialisincreased,andwaterleavesthesievetube.Withthemovementofwaterintothesievetubeatthesourceandoutofitatthesink,thesugarmoleculesarecarriedpassivelybythewateralongtheconcentrationgradientbetweensourceandsink.目前二十頁\總數(shù)二十六頁\編于十四點(diǎn)(a)Assucrose(s)isactivelytransportedintosieveelements,ΨsandΨcellbecomemorenegative,movingawayfromequilibriumwithcompanioncellsandotherneighboringcells.Watermovesintothesieveelements,squeezingphloemsapoutthroughthesievepores.Becausethesugarywaterescapesthroughsievepores,highpressuredoesnotbuildup,sothepressurepotentialdoesnotriseandstoptheinfluxofwater.Thewaterpotentialsofsieveelementsandsurroundingcellsneverreachequilibriumaslongassucroseisbeingpumped.Thesourceoftheglucosemaybephotosynthesisorthebreakdownofstarch.(b)Insinks,sucroseisactivelytransportedoutofsieveelements,andallprocessesworkinreversecomparedwithsources.Insomesinks,mostofthesucroseisconvertedtoglucoseandthenpolymerizedtostarch(storageorgans),isrespired(mosttissues),orisusedtoconstructnewcompounds(growingtissues).目前二十一頁\總數(shù)二十六頁\編于十四點(diǎn)BOX:P-proteinhypothesisP-protein,foundasafinenetworkadjacenttotheplasmamembraneinnersurfaceofuninjuredsieveelements.Whenphloemisruptured,thephloemsapinitiallysurgestowardthebreak;thisrapidmovementsweepstheP-proteinintothecellcenter,whereitbecomesatangledmass.Whenitiscarriedtoasieveareaorsieveplate,the