植物体内有机物运输和分配 (2).ppt

BOX:transfercells(转移细胞)Therateatwhichmaterialcanbeactivelytransporteddependsonthenumberofmolecularpumpspresent,whichinturndependsonthesurfaceareaoftheplasmamembrane:Thelargerthemembrane,themoremolecularpumpsitcanhold.Incertainspecializedtransfercells,thewallsaresmoothontheoutersurfacebuthavenumerousfinger-likeandridgelikeoutgrowthsontheinnersurface.Theplasmamembraneispressedfirmlyagainstalltheconvolutionsandthushasamuchlargersurfaceareathanitwouldifthewallwereflat.Consequently,roomisavailableformanymolecularpumps,andhigh-volumetransportcanoccuracrossthesetransferwalls.Transfercellsarefoundinareaswhererapidshortdistancetransportisexpectedtooccur:inglandsthatsecretesalt,inareasthatpassnutrientstoembryos,andinregionswheresugarisloadedintooroutofphloem.第2页,共23页，星期六，2024年，5月(a)Oncereleasedfromacell,amoleculediffusesinaseriesofrandomshortpathsasitcollideswithandbouncesoffothermolecules.Probabilityfavorsitsenteringaneighboringcell(molecules1,2,and3),butitcandiffuselaterallyalongthewallaswell(molecules4and5).(b)Inmanyglands,theapopIastislarge,somovementbetweencellsmaybefasterandeasierthanmovementwithincells.Suchglandsoftenhavealiningofcompacttissuethatisolatesthegland,preventingthesecretedmaterialfrompermeatingthewholeregion.第3页,共23页，星期六，2024年，5月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。第4页,共23页，星期六，2024年，5月水分和同化物运输的途径比较第5页,共23页，星期六，2024年，5月Diagramshowingbasicelementsinthecirculationofwater,inorganicions,andassimilatesintheplant.Waterandinorganicionstakenupbytherootmoveupwardinthexyleminthetranspirationstream.Somemovelaterallyintotissuesoftherootandstem,whileothersaretra