(B)(A)Sieve plateP-proteinSieve tubeSieveplateelement8poregogModifiedLateral sieveg80plastidarea80880Sieve tubeelementCompanionSmoothcellendoplasmicreticulumBranchedplasmodesmatCytoplasmVacuolePlasmamembraneChloroplast酒ThickenedFigure 6-1primary waliNucleusSieveplateMitochondrioporeSieveplate
Figure 6-1
Figure 6-2MiddlelamellaProtein particles onPlasmamembraneouter leaflet of ERCellwallTonoplastEndoplasmicCytoplasmreticulumVacuolePlasmodesmaDesmotubuleProtein particles onProteinparticles oninnerleafletofERinnerleafletofwithappressedERplasmamembrane
Figure 6-2
(B)ERPlasmamembrane(A)CytoplasmEndoplasmicreticulumDesmotubuleNeckCentralrodCell wallDesmotubulePlasmamembraneMiddleCell walllamellaCentral cavityCytoplasmicsleeveERCrosssectionsFIGURE1.27Plasmodesmatabetweencells,(A)Electronmicrograph of a wall separating two adjacent cells,showingOOCentral cavitytheplasmodesmata. (B)Schematicview ofa cell wall withtwoplasmodesmatawith different shapes.The desmotubuleCentral rodis continuous withthe ER ofthe adjoining cells.Proteins lineSpokelikeCytoplasmicthe outer surface ofthe desmotubuleand the inner surface offilamentoussleevetheplasma membranethe two surfaces arethought tobeproteinsconnected by filamentousproteins.Thegapbetweentheproteins lining the two membranesapparently controls themol-ecularsievingpropertiesofplasmodesmata.(AfromTilneyFigure 6-2-1etal.1991;BafterBuchananetal.2000.)
Figure 6-2-1
AcquiringphloemsapAphidsare small insectsthatremovenutrientsfromphloembymeans ofa needlelike mouthpart called a styleta.Aphid withstylet inplace.b.When theexperimenterphloenremovestheaphid'sbody,phloemsapisavailablesapcollection andanalysis.styletstyletFigure 6-4phloemb
Figure 6-4
MouthpartSieve tubememberMouthpart(b)25μmaAphidsusedtostudytranslocationinphloem.(a)Matureaphid,a tiny insectabout3to6mmin length,feedingona stem.(b)LMofphloemcells,showinga sieve tube memberthat has been penetrated by theaphid mouthpartFigure 6-4-1(a,DwightKuhn;b,M.H.Zimmerman,Science,Vol.133,pp.73-79[Fig.4],13Jan1961.Copyright2002bytheAmericanAssociationfortheAdvancementofScience
Figure 6-4-1