植物生理学课件：Chapter 5 同化物的运输与分配

Chapter5同化物的运输与分配

p146-1671.同化物的运输2.同化物的装入与卸出3.同化物的配置与分配4.影响同化物运输与分配的外部因素Focuson:Section1

Translocationsystemsofassimilateinplant一、代谢的区室化Section2TranslocationsystemsofassimilateinplantFigure5-1showscompartmentationinplantcell一、代谢的区室化FruitstoresphotoassimilateLeafmakesphotoassimilateFigure5-4showscompartmentationinplantorgans二、同化物运输的途径（一）胞内和胞间运输1.胞内运输2.胞间运输质外体和共质体Figure5-2Thestructureofplasmodesma数目多106~107/mm2inplant

Theplasmodesmais3nm,cantransportthelimitedmoleculeof800-1000D,butvirus10000D.Figure5-3showsconceptualmodelforthecell-to-celltraffickingofviralRNA(vRNA)inuninfectedplants.MP：MoveproteinFigure5-4showsaconceptualmodelforcell-to-celltraffickingofspecificproteinsofasizelargerthanpassiveSEL.Plasmodesmafunction：Substancetransportandinformationtransduction.物质运输与信息传递Lessresistancetosubstancetransportcellbycellbecauseofnotransmembranetransport.运输阻力小Suchastheresistanceforplasmamembraneis0.31Ω/m2，fortonoplast0.1Ω/m2andforplasmadesma0.05/Ωm2.3.Shortdistancetranslocationisalternativebetweenapoplastandsymplast

3.共质体和质外体交替运输Fig5-3

alternativetransportbetweenapoplastandsymplast叶脉转移细胞的功能（源端装入，库端卸出）

Fig5-8TransfercellsTransfercells:Agroupofspecificcellsexistintheterminalinconducttissue,flowerorfruits输导组织末端及花果器官特化细胞Characteristicsinstructureandmetabolism:Largesurfaceareaofcellbecausecellwallandplasmamembraneshowrugocity(ingrowth).Abundantcytosolandorganelles,highmetabolicactivity.Companioncellsandintermediarycellsareconsideredastransfercells.Mainfunction：Loadingassimilateintophloemfromsourceandunloadingassimilateintosinkcellfromphloemorotherconducttissue.Figure5-10Sieveelementsandcompanioncells（二）器官间的运输RinggirdlingRinggirdlingforcertaintimeformsahumpFigure5-11RinggirdlingresultsinthehumpFigure5-11conducttissue1.Sievetubeandcompanioncell（SE/CC）areinangiospermFigure5-12amodelofsieveelementandcompanioncellsFigure5-13PhotographofsieveelementandcompanioncellbyelectronmicroscopeP-

protein：与植物各类和筛管分子的成熟度有关.幼嫩筛管：扭曲盘绕的球形或纺锤形成熟筛管：管状或丝状的结构功能：促进物质运输；防止汁液的流失。寿命：有长（2-10），有短（一个生长季节）Section3Phloemtransportofassimilates

Fig5-14Confocalmicroscopeshowsphloemtransport激光共聚焦显微镜3.1ElementsofphloemsapHowtogetphloemsap?Figure5-15harvestphloemsapTable5-1phloemsapfromyucca

Totaldrymatter17.1-19.2(%)

K1.68Aminoacid(%)EC(ms/cm)1.03Mg0.051Gln58pH8.0-8.2Ca0.014Val10Components(mg/ml)Na0.0014Ser,Gly7Sucrose150-165Zn0.0021(Iso-)Leu6Glucose2-4Fe0.0041Lys5Fructose2-4Mn0.0005Glu4Protein0.5-0.8Cu0.004Ala2Aminoacid6.3-10.1Mo0.00001Asntrace

TotalP0.301ProtracePi0.105Nitrate0丝兰Componentsinphloemsap:1.Sugars.Sucrose>90%，asmallnumberofsorbitol,mannitolandoligoseincludingraffinoseandstachyose.Mainsorbitolinroseplantphloem.2.AminoacidsandAmides.Glu

orAteins(enzymes,ATPase)andnuclearacid(smallmRNA).4.Planthormones,ATP,glucolipid,anicacids.Mal.6.inorganicions：cations>anions，mostK+forcations,mostPiforanions,andwithoutNO3-LowerH+,higherpH(7.5-8.5)andK+concentrationinsieveelement;HigherH+concentration,lowerpH(5-6)andK+concentrationoutsidesieveelement.3.2

Transportdirectionisdeterminedbysink-source

1.Fromsourcetosink---bidirectionalway.14CFigure5-16bidirectionalwaySource——metabolicsource,referredastheorgansortissueswhichproduceor/andtransportsoutassimilate,suchasdevelopedleaf，roottuberortuberduringgermination.

Sink——metabolic，referredastheorgansor/andtissueswhichconsumeor/andstoreassimilate,suchasroot，seed,fruit,roottuberandtuberduringdeveloping.Slightringgirdlinginbranchcanenhancefruitsetting.“树怕剥皮，不怕烂心”？RinggirdlingAfterringgirdlingbranchthebarkcanformahump(hypertrophicgrowth)

.Figure5-13Ringgirdlingresultsinthehump2.Ipsi-lateraltransportofassimilateisdominantFigure5-14Ipsi-lateraltransportofassimilate

3.Assimilatesindifferentsourcesaretranslocatedbydifferentconducttissues.Assimilatemadeinleafistransportedtorootbyphloem.Assimilatestoredintuberistransportedtobudforgerminationbyphloem,too.Assimilatestoredinthetreerootistransportedtobudandyoungleafbyxylem4.RateofassimilatetransportinphloemVelocity,masstransferrate(1)Velocity:thelineardistancetraveledperunittimeInmostplantabout50-250cm/h,suchassoybean84-100,grape60，sugarcane(C4plant)300-600cm/h.Sucroseis107cm/h,PiandH2Oare87cm/h.Masstransferrate,thequantityofmaterialpassingthroughagivencrosssectionofphloemorsieveelementsperunittime.Valuesformasstransferraterangefrom1to15gh–1cm–2ofsieveelements3.4Phloemtranslocationoccursbymasstransfer

1.Pressure-flowhypothesis

Thepressure-flowmodel,firstproposedbyErnstMünchin1930,statesthataflowofsolutioninthesieveelementsisdrivenbyanosmoticallygeneratedpressuregradientbetweensourceandsink(ΔYp).Thepressuregradientisestablishedasaconsequenceofphloemloadingatthesourceandphloemunloadingatthesink..Figure5-15Amodelofpressureflowhypothesis

OsmoticmeterAloading，OsmoticmeterBunloadingBASieveelementP-protein(2).Contractiveproteinhypothesis

P-proteinusesATPtocontractandpushesphloemflow.Figure5-16structureofsieveelement(3)Electroosmoticflowhypothesis-------------------------------------------------------------------+CationflowsPotentialdifference-cationanionFigure5-15illustrationofelectroosmoticflowhypothesis第二节、同化物的装入与卸出一、韧皮部的装入质外体途径、共质体途径细胞壁非质体质膜胞间连丝叶肉细胞维管束鞘细胞韧皮薄壁细胞伴胞筛管分子共质体CO2最小的叶脉源叶中韧皮部装载示意图1、装载途径：共质体途径；质外体途径2、装载机理：H+—蔗糖协同转移模型-质外体途径装载受载体调节，其依据是：对被装载物质（如蔗糖）有选择性；需要能量；具有饱和效应蔗糖－质子同向运输器质外体途径蔗糖载体ATP酶质外体共质体外（+）内（－）筛管、伴胞SSH+H+H+H+K+K+K+K+PH5.5PH8.5低K+高K+低S高S寡糖转运的多聚体－陷阱模型维管束鞘细胞居间细胞筛分子半乳糖葡萄糖果糖共质体途径二、韧皮部的卸出第三节、韧皮部的卸出1、卸出途径：蔗糖先水解后进入代谢库－质外体途径（1）蔗糖不水解直接进入代谢库－质外体途径（2）和共质体途径（（3）胞间连丝）2、卸出机理：主动过程；被动过程液泡膜细胞壁质膜液泡接受细胞韧皮部细胞（筛管分子、伴胞）库组织中蔗糖卸出的可能途径示意图第三节同化产物的配置与分配一、配置代谢利用、合成暂时贮藏化合物、输出到其它二、有机物的分配分配方向：由源到库，优先供应生长中心同侧运输，就近供应侧向运输，源间互补有机物分配－优先供应生长中心有机物分配－就近供应、同侧运输有机物的同侧运输有机物分配控制因素供应能力：代谢源竞争能力：代谢库运输能力：运输途径Fig5-20Section5Factorsaffectingassimilatetranslocation

5.1Internalfactors1.Sucrosecontent:

S↑，export↑.2.

ATP↑、Pi↑，TP↑，export↑.Insugarbeet,K/Na↑，starch↑，S↓，export↓.3.Planthormones:IAA、GA、CTK↑，import↑4.Sizeinsink,sink

↑，import

↑.4.2Environmentalfactors1.Water:notenough,waterpotential↓，Pn↓，S↓，resistance↑，transport↓.2.Light:light↓，Pn↓，S↓，export↓Transportduringdaytime>oneatnight.3.Temperature：optimum20-30℃.T↓，transport↓becauseofrespiration↓，energy↓，Pn↓photoassimilate↓，viscosity↑，callose↑.

HighT，transport↓，duetorespiration↑，Pn↓，photoassimilate↓，viscosity↑，callose↑Largerdifferenceintemperaturefavorstransportbecauseofaccumulationofphotoassimilate.4.Mineralnutrition，B、P、K.1.WhatfactorsdeterminewhethertheproductofthePCRcyclewillbeconvertedtostarchinthechloroplastorsucroseinthecytosol?2.Describethestructureofmaturephloemtissue.Whatarecauseshypertrophicgrowthaboveagirdlewound?3.Describethesource–sinkconcept.Towhatextentaresource-sinkrelationshipsinvolvedindeterminingthedirectionandrateoftranslocationinthephloem?4.Howaresugarsloadedintothephloemsievetubersatthesourceandremovedatthesink?5.Distinguishbetweenallocationandpartitioning.Whatfactorsdetermineallocationofcarbonwithinasourceleaf?Whatfactorsdeterminepartitioningbetweenmorethanonepotentialsink?3.5

Loadingandunloadinginphloem1.Phloemloadingisthroughthesucrose–H+

symportersSucrosefrommesophyllcelltoapoplast,thentoSE/CCintosieveelement.Requirementforenergyandagainstconcentrationofsucrose.Fig5-17Thisautoradiographshowsthatlabeledsugarmovesfromtheapoplastintosieveelementsandcompanioncellsagainstitsconcentrationgradientinsugarbeet(Betavulgaris).Labelaccumulatesinthesmallveins,sieveelements,andcompanioncellsofthesourceleaf,indicatingtheabilityofthesecellstotransportsucroseagainstitsconcentrationgradient.(FromFondy1975,courtesyofD.Geiger.)Figure5-18ATP-dependentsucrosetransportinsieveelementloading.Inthecotransportmodelofsucroseloadingintothesymplastofthesieveelement–companioncellcomplex,theplasmamembraneATPasepumpsprotonsoutofthecellintotheapoplast,establishingahighprotonconcentrationthere.Theenergyinthisprotongradientisthenusedtodrivethetransportofsucroseintothesymplastofthesieveelement–companioncellcomplexthroughasucrose–H+

symporter.Figure5-18Polymer-trappingmodelofphloemloading.(2)PhloemunloadingFig5-19Pathwaysforphloemunloading.Thesieveelement–companioncellcomplex(CC/SE)isconsideredasinglefunctionalunit.Thepresenceofplasmodesmataisassumedtoprovidefunctionalsymplasticcontinuity.Anabsenceof