Plantcell anatomy.a.Generalizeddrawing.b,Transmissionelectronmicrographofyoungleaf cell.SeeTable 4.1fora description ofthesestructuresalonawitha listingoftheirfunctionsmicrotubule-nuclearporecentralvacuolechromatin-nuc-nucleolus-nuclearenvelopechioroplast-ribosomeactinroughERfilament.SmoothERplasmamembranecellwallCcytosolGolgiapparatusmitochondrionVintracellularspacemiddlelamellacell wallofadjacentcellFigure 1-0
Figure 1-0
OUTSIDEOF CELLWatermoleculesWater-selectivepore (aquaporin)MembranebilayerEigure I-1CYTOPLASM
⚫ Figure 1-1
lesswaterOsmosisdemonstration(highera.Athistletube,coveredatthebroad end bypercentagesolutionrisesadifferentiallypermeablemembrane,containsof solute)duetomovementa10%sugar solution.Thebeakercontainsaofwater toward5%sugar solution.b.The solute(greennetmovementofwaterhigher percentagecircles) is unableto passthroughtheto insideofthistletubeof solutemembrane,butthewaterpassesfreelythrough in both directions.Anet movementofsoluteWwatertowardthe insideofthethistletubeoccurs becausethethistle tubehas a higherpercentage ofsolute.c.In the end,thelevelofthe solution rises inthethistletube until10%morewaterhydrostatic pressure increases to the levelof(lowerosmoticpressure.percentage5%of solute)membranec. In the enda. In the beginningb.In themeantimeFigure 1-2
Figure 1-2
(a)Inhypotonicsurroundingsthe vacuole of aplant cell fillsbuttherigid cell walls preventthecell fromexpanding.Thecells of this healthybegoniaplantare turgid. (b and e)Whenthebegoniaplant isexposedtoahypertonicsolution,itscellsbecomeplasmolyzedastheylosewater.Theplantwiltsandeventuallydies.(DennisDrenner)PlasmaNucleusmembraneVacuoleVacuoleVacuolarmembrane(tonoplast)CytoplasmPlasmamembraneFigure 1-2-1(a)(b)(c)
Figure 1-2-1
OsmosisinHypertonicHypotonicIsotonicanimal and plant cells.ConditionsConditionsConditionsAnimalCellsplasmamembranec.Water exits thecell,whichb.Waterentersthecell,whicha.Nonetmovementofwatermayburst(lysis)duetoshrivels (crenation)intoandoutofthecellosmoticpressure,Plant拉蓬Cells-Cwallplasmamembranechloroplastf.Vacuoles losewater,thee.Vacuolesfillthewater,turgord.Nonetmovementof waterFigure 1-2-2cytosolshrinks (plasmolysis)pressuredevelops,andintoandoutofthecelland chloroplastsareseen inchloroplastsareseen nexttothe cell wall.thecenterofthe cell
Figure 1-2-2
(A) Purewater(B)SolutioncontainingO.1 MsucroseO.TMSucrosesolutionPurewaterypOMPaP--0.244MPap=0MPayw=yp+ysS-OMPa-0-0.244MPayw=yp+y--0.244MPa-OMPa(C)Flaccidcelldroppedintosucrosesolution(D)ConcentrationofsucroseincreasedFlaccid cellTurgid cellYp=OMPaYp-0.488MPas--0.732MPaY's--0.732MPaYw=-0.732MPaPw--0.244MPa++0.3 M SucroseCellafterequilibriumsolutionCellafterequilibriumyw=-0.732MPayp-OMPayw--0.244MPays--0.732MPas=-0.732MPa=-0.732MPayp-yw-y,-oMPaPw--0.732MPaYp=yw-y,=0.488MPaPressure applied to cell(E)Appliedpressuresqueezesouthalfthewater,thus doublingy.fram-0.732to=1.464MPao,1MSucrosesolutionCell in initialstateCell in final state+yw--0.244MPayw=-0.244MPaNs=-1.464MPa=-0.732MPay-yw-y0.488MPayp-Yw-s-.1.22.MPa个Fiveexamplesillustratingtheconceptofwaterpotentialanditscom.FIGURE3.9ponents.(A)Purewater(B)Asolutioncontainingo.1Mstucrese(C)Aflaccidcelltinair)sdroppedintheo,IMsucrosiesolutionBecauscthestartingwaterpoten-tialofthecellislessthanthewaterpotentialofthesolution,thecelttakesupwater,Aftereguilibration,theWaterpotontialofthecollrisustoegualthewaterpotentiatofthesolution,andtheresultisacclwithapositivoturgorpressire.(D)IncreasingtheconcentrationofsucroseinthesolutiontmakesthecellosewatcrTheincreasedsucrosococontraton.lovorsthsoiutonwatorpotontal,drawswaterouutfromthecell,andtherebyreducosthecell'sturgorpressure,Inthiscasetheprotoplastisabletopullawayfromthe cellwall (e,thecell plasmolyzes)becausesucrosemolecufesareabletopassthroughtherelativelylargeporesofthecellwalls.Incontrast,whenacelldesiccatesinair(egtheflaccidcen inpanelC)plasmolysisoesnotoccurbecausuthewaterheldby capillaryforeesinthecellwallspreventsairfrom inaltratingintoanyvoid betweentheplasmamcmbraneFigure 1-2-3and thecellwall(E)AnotheriwaytomakethecelllosewateristopressitslowlybetweentwoplatosInthiscase,halfofthecelwaterisrmoved,socelosmoticpotentialincreasus byaFactorof2
Figure 1-2-3
+1.0p0.5OPdW-0.5-1.0-4S-1.5H-2.05-2.0.91.01.11.21.31.41.5Fig. 1-3Relativecellvolime
Fig. 1-3
endodermispericyolephloemxylemcortexepiderrmisroothairVascular cylinderb.50um(cross section)Zone ofMaturationendodermiscortexxylemotvascoularCaspariancylinderstripVascularCylinderwater andmineralsZone ofc,EndodermisElongation(nurtace Viewot cells)Zone ofCell DivisionRootCapRoottipa(longititudinalsection)Dicotroottip.a.Theroottip is divided into tour zones,bestseenin a longitudinalisection suoh as this,b.The vascularcylinder of a dicot rootFigure 1-5-0Containsthe vasculartissue.Xylem ie typically starshaped,andphloemliesbetween the points orthestar o,Endodermisshowingthe Casparian strip, a layer or lignin and suberin in cell walls.BecauseortheCasparian strip,waterand minerals mustpassthrough the cytoplasm of endodermal cells.In this way,endodermalcells regulate the passage ofmineralsinto thevascular cylinder
Figure 1-5-0
EndodermisCasparianstripSymplasticandtransmembranepathwaysPericycleXylemPhloemCortexEpidermisFIGURE4.3Pathwaysforwateruptakebytheroot.Throughthecortex,watermayApoplastpathwaytravel viatheapoplastpathway,thetransmembranepathway,and thesymplastpathway.In the symplastpathway,waterflowsbetween cells through the plasmodesmatawithoutcrossingtheplasmamembrane.Inthetransmembranepathway,watermoves acrosstheplasma membranes,witha shortvisitto thecell wall space.Figure 1-5Attheendodermis,theapoplastpathwayisblockedbytheCasparian strip
Figure 1-5
(B)(A）Figure17.23ABA-induced stomatalclosure.Epidermal strips of Commelina communis L.incubated inbuffer (10mMPipespH6.8)containing50mMKCland supplied withCO,-freeair.The stomata areopen wide aftertwotothreehours(A).When transferred tothe same solution plus10μMABA,the pores close completelywithin 10 to30minutes (B),Figure 1-6-0
Figure 1-6-0