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1、植物体内有机物运输和分配(a)Oncereleasedfromacell,amoleculediffusesinaseriesofrandomshortpathsasitcollideswithandbouncesoffothermolecules.Probabilityfavorsitsenteringaneighboringcell(molecules1,2,and3),butitcandiffuselaterallyalongthewallaswell(molecules4and5).(b)Inmanyglands,theapopIastislarge,s
2、omovementbetweencellsmaybefasterandeasierthanmovementwithincells.Suchglandsoftenhavealiningofcompacttissuethatisolatesthegland,preventingthesecretedmaterialfrompermeatingthewholeregion.6.1.2longdistancetransport (长距离运输)6.1.2.1pathway(途径)：phloem(韧皮部)。Girdlingexperiment(环割试验)、radioacti
3、vetracer(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。14CO2示踪技术：TwoleafletsofabroadbeanplantwereenclosedinaPlexiglascontainerandexposed14CO2andlightfor35minutes.Duringthattime,14CO2wasincorporatedintosugars,whichwerethentransportedtootherpartsoftheplant.6.1.2.2韧皮部组成由筛管(sievetube)、伴胞(comp
4、anioncell)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)(a)Longitudinal(radial)viewofsecondaryphloemofyew(Taxuscanadensis),showingverticallyorientedsievecells,strandsofparenchymacells,andf
5、ibers.Partsoftwohorizontallyorientedrayscanbeseentraversingtheverticalcells.(b)Detailofportionofthesecondaryphloemofyew,showingsieveareas,withcallose(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
6、方法证明。(a)Aphid(Longistigmacaryae)feedingonabasswood(Tiliaamericana,椴木)stem.Adropletof"honeydew"canbeseenemergingfromtheaphid.(b)Aphotomicrographshowingpartofthemodifiedmouthparts(stylets)oftheaphidinasievetubeofthesecondaryphloemofthebasswoodstem.Anarrowpointstothetipsofthestylers.6.2
7、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,butstoragetissuesmayalsoserveasimportantsour
8、ces.Allplant
