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1、植物体内有机物运输和分配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。水分和同化物运输的途径比较Diagramshowingbasicelementsinthecirculationofwater,inorganicions,andassimilatesintheplant.Waterandinor
2、ganicionstakenupbytherootmoveupwardinthexyleminthetranspirationstream.Somemovelaterallyintotissuesoftherootandstem,whileothersaretransportedtogrowingplantpartsandmatureleaves.Intheleaves,substantialamountsofwaterandinorganicionsaretransferredtothephloemandareexportedwithsucro
3、seintheassimilatestream.Asearlyastheseventeenthcentury,MarcelloMalpighiofItalynoticedthat,whenaringofbarkwasremovedfromastem(a),thetissuesabovetheringbecameswollen(b).Hecorrectlyinterpretedthisphenomenonasnewgrowthofwoodandbarktissuesstimulatedbyanaccumulationoffoodmovingdown
4、fromtheleavesandinterceptedatthering.Malpighistudiedtheeffectofringingatdifferenttimesoftheyearandfoundthatnoswellingoccurredduringthewintermonths.Girdlingexperiment(环割试验)14CO2示踪技术：TwoleafletsofabroadbeanplantwereenclosedinaPlexiglascontainerandexposed14CO2andlightfor35minute
5、s.Duringthattime,14CO2wasincorporatedintosugars,whichwerethentransportedtootherpartsoftheplant.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,S
6、E-CC)(a)Longitudinal(radial)viewofsecondaryphloemofyew(Taxuscanadensis),showingverticallyorientedsievecells,strandsofparenchymacells,andfibers.Partsoftwohorizontallyorientedrayscanbeseentraversingtheverticalcells.(b)Detailofportionofthesecondaryphloemofyew,showingsieveareas,w
7、ithcallose(stainedblue)onthewallsofthesievecells,andalbuminouscells.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。(a)Aphid(Longistigmacaryae)feedingonabasswood(Tiliaamericana,椴木)stem.Adropletof"honeydew"canbeseenemergingfromtheaphid.(b)Apho
8、tomicrographshowingpartofthemodifiedmouthparts(stylets)oftheaphidina
