Summary A plant is an integrated system which: 1. Obtains water and nutrients from the soil. 2. Transports them
3. Combines the H2O with CO2 to make sugar. 4. Exports sugar to where it’s needed
Today, we’ll start to go over how this occurs Transport in Plants – Outline
I.I. PlantPlant waterwater needsneeds II.II. TransportTransport ofof waterwater andand mineralsminerals A.A. FromFrom SoilSoil intointo RootsRoots B.B. FromFrom RootsRoots toto leavesleaves C.C. StomataStomata andand transpirationtranspiration
WhyWhy dodo plantsplants needneed soso muchmuch water?water? TheThe importanceimportance ofof waterwater potential,potential, pressure,pressure, solutessolutes andand osmosisosmosis inin movingmoving water…water… Transport in Plants
1.1. AnimalsAnimals havehave circulatorycirculatory systems.systems.
2.2. VascularVascular plantsplants havehave oneone wayway systems.systems. waterwater Transport in Plants
•• OneOne wayway systems:systems: plantsplants needneed aa lotlot thanthan samesame sizedsized animals.animals. moremore •• AA sunflowersunflower plantplant “drinks”“drinks” andand “perspires”“perspires” 1717 timestimes asas muchmuch asas aa human,human, perper unitunit ofof mass.mass. Transport of water and minerals in Plants WaterWater isis goodgood forfor plants:plants: 1.1. UsedUsed withwith CO2CO2 inin photosynthesisphotosynthesis toto makemake “food”.“food”. 2.2. TheThe “blood”“blood” ofof plantsplants –– circulationcirculation (used(used toto movemove stuffstuff around).around). 3.3. EvaporativeEvaporative coolingcooling.. 4.4. UsedUsed forfor turgorturgor pressurepressure toto holdhold plantplant erect.erect. Transport of water and minerals in Plants WaterWater (with(with minerals)minerals) -- entersenters fromfrom thethe soil,soil, travelstravels throughthrough xylemxylem exitsexits thethe leavesleaves (through(through stoma).stoma).
WhatWhat makesmakes itit move?move? Transport of water and minerals in Plants
WhatWhat makesmakes itit move?move?
WaterWater potentialpotential == thethe tendencytendency ofof waterwater toto movemove fromfrom oneone placeplace toto anotheranother
acrossacross aa membrane.membrane.
purepure waterwater (would(would havehave WP=0WP=0)) Transport of water and minerals in Plants WaterWater potentialpotential == thethe tendencytendency waterwater toto movemove WaterWater isis usuallyusually aa solutionsolution •• \\ potentialpotential pullspulls water.water. •• ⊕⊕ potentialpotential pushespushes water.water.
•• Thus,Thus, waterwater flowsflows towardtoward moremore \\ waterwater potential.potential. Transport in Plants WaterWater potentialpotential ((ΨΨ PsiPsi)) == PressurePressure potentialpotential ++ SoluteSolute PotentialPotential
ΨΨ==ΨΨp++ΨΨss
PressurePressure potential,potential, ΨΨpp == hydraulichydraulic pressure.pressure. (like(like airair pressurepressure inin tires).tires). Transport in Plants WaterWater potentialpotential ((ΨΨ PsiPsi)) hashas 22 parts,parts, ΨΨ==ΨΨp++ΨΨss
PressurePressure potential,potential, ΨΨpp == hydraulichydraulic pressure.pressure. (like(like inin aa car’scar’s brakebrake line,line, oror likelike airair pressurepressure inin tires).tires). Transport in Plants •• WaterWater potentialpotential ((ΨΨ)) hashas 22 parts,parts, ΨΨ==ΨΨp+p+ΨΨss SoluteSolute potential,potential, ΨΨss == tendencytendency ofof aa liquidliquid toto movemove acrossacross aa membranemembrane -- Think oftoto itthethe like sideside a tug withwith of war aa higher higher– concentrationconcentration The water ofofis thedissolveddissolved ‘rope’ solutes.solutes.
WaterWater flowsflows towardtoward moremore \\ solutesolute potentialpotential (unless(unless resistedresisted byby ⊕⊕ pressurepressure potential).potential). How water potential works Ψ=Ψp+Ψs
In the tube: ΨΨss == --0.40.4 ΨΨpp == 00 ΨΨ == ??
Beaker has distilled water with Ψ = 0
Predictions? Fig 36.2 How water potential works Ψ=Ψp+Ψs Water moves toward more \ osmotic potential. • Difference in Ψ so – • BeakerÆTube • Pressure potential (from gravity on the column of water) increases • Until it is equal and opposite to the \ osmotic pressure. osmotic pressure. Water enters plant cells Ψp = 0.15 through Ψs = -0.15 osmosis Fig 36.2 How water potential works Ψ=Ψp+Ψs
Or Resistance to entry of water E.g. Cell walls (Here a piston)
Ψs doesn’t change
But water still leaks in to raise Ψp until balanced water potentials Fig 36.2 Water potential
ΨΨ==ΨΨpp++ΨΨss
ThisThis isis how:how: •• PlantsPlants getget supportsupport (pressure)(pressure) •• WaterWater movesmoves intointo andand outout ofof plantplant cellscells Turgor provides support and keeps plants from wilting •• WaterWater entersenters cellcell byby osmosisosmosis ––
•• ⊕⊕ pressurepressure potentialpotential ((turgorturgor pressurepressure)) increasesincreases andand balancesbalances thethe \\ osmoticosmotic pressurepressure (it(it isis equalequal andand opposite).opposite).
•• WaterWater stopsstops movingmoving -- thethe cellcell isis turgid.turgid. Summary of Water Potential •• WaterWater potentialpotential == thethe tendencytendency ofof aa solutionsolution toto absorbabsorb oror releaserelease waterwater
•• WaterWater flowsflows towards?towards?
OrOr -- \\ waterwater potentialpotential winswins thethe tugtug ofof warwar Summary of Water Potential SoluteSolute potential,potential, ΨΨs:s:
K+ K+ K+ K+ K+ K+ H20 K+ K+ K+ K+ Transport of water and minerals in Plants •• OsmosisOsmosis hashas aa majormajor influenceinfluence gettinggetting waterwater fromfrom thethe soilsoil toto thethe rootroot xylemxylem..
•• PressurePressure potentialpotential isis responsibleresponsible forfor movingmoving waterwater throughthrough thethe xylemxylem toto thethe leavesleaves (and(and air)air).. Transport in Plants
•• OsmosisOsmosis -- waterwater movementmovement betweenbetween livingliving cells.cells. •• SoilSoil ÆÆ rootroot xylem,xylem, waterwater passespasses throughthrough livingliving cellscells
Why? From the soil to the root xylem
•• WaterWater movesmoves freelyfreely throughthrough cellcell wallswalls andand intercellularintercellular spaces,spaces, but,but, Fig 36.5 •• CasparianCasparian stripsstrips preventingpreventing waterwater andand ionsions flowflow •• HasHas toto goesgoes thruthru cytoplasmcytoplasm ofof thethe endodermisendodermis cellscells.. Movement of minerals into the cells is through active transport •• MineralMineral ionsions movemove acrossacross membranemembrane transporttransport proteins.proteins. •• ActiveActive transporttransport againstagainst aa concentrationconcentration gradient.gradient.
Fig 36.3 Transport in Plants
MineralMineral ionion concentrationsconcentrations affectsaffects solutesolute potentialpotential PlantsPlants control:control: •• thethe concentrationconcentration ofof mineralmineral ionsions inin livingliving cells,cells, hencehence •• theythey controlcontrol osmosisosmosis inin rootsroots.. 2 Control Points with Transport Proteins •• EndodermisEndodermis –– waterwater fromfrom cortexcortex ÆÆ endodermisendodermis
•• CellsCells nearnear xylemxylem Fig 36.4 createcreate anan osmoticosmotic gradientgradient thatthat movesmoves waterwater intointo thethe xylem.xylem. Transport in Plants MineralMineral ionsions movemove outout ofof thethe cellcell (active(active transport)transport) WaterWater potentialpotential isis moremore negativenegative outsideoutside SoSo waterwater movesmoves outout ofof thethe cellcell (osmosis)(osmosis)
SO:SO: MineralsMinerals –– active/directactive/direct WaterWater followsfollows passivelypassively Transport in Plants •• XylemXylem -- movementmovement isis controlledcontrolled byby pressurepressure potentialpotential (hydraulic(hydraulic pressure).pressure).
•• WaterWater andand mineralsminerals areare pulledpulled ((\\ pressurepressure potential)potential) throughthrough thethe xylemxylem withoutwithout expendingexpending energy.energy. How?How? How are water and minerals are pulled through the xylem?
•• TranspirationTranspiration –– evaporationevaporation ofof waterwater fromfrom leavesleaves
•• TensionTension –– inin thethe xylemxylem sapsap fromfrom transpirationtranspiration
•• CohesionCohesion –– inin thethe xylemxylem sapsap alongalong thethe plantplant It’s like sucking on a straw……
WaterWater diffusesdiffuses outout ofof leaf.leaf. WaterWater evaporatesevaporates offoff leafleaf cellscells toto replacereplace it.it. ThisThis pullspulls waterwater fromfrom veins.veins. ThisThis tensiontension pullspulls thethe waterwater columncolumn upup
Fig 36.8 It’s like sucking on a straw……
•• InIn thethe xylemxylem -- movementmovement isis controlledcontrolled byby pressurepressure potentialpotential (hydraulic(hydraulic pressure).pressure).
Because:Because: DryDry airair hashas veryvery negativenegative ΨΨ ((ΨΨ == --9595 MPaMPa)) SoilSoil isis betweenbetween ––0.010.01 toto ––33 MPaMPa Transport of water and minerals in Plants •• ThereThere isis negativenegative waterwater potentialpotential inin stems.stems. •• WhatWhat happenshappens ifif youyou werewere toto cutcut thethe basebase ofof aa stem?stem? •• BreakBreak thethe cohesioncohesion inin thethe waterwater columncolumn Transport in Plants
•• WithWith highhigh humidityhumidity wetwet soilssoils somesome plantsplants willwill eveneven havehave waterwater pushedpushed outout ofof thethe leavesleaves == ““guttationguttation””
•• “root“root pressure”:pressure”: osmoticosmotic pressurepressure duedue toto higherhigher solutesolute concentrationconcentration inin rootroot xylemxylem sapsap thanthan inin thethe soil.soil. Summary of Root to Leaf Water Movement •• OsmosisOsmosis == motormotor forfor gettinggetting waterwater fromfrom thethe soilsoil intointo thethe rootroot xylem.xylem. •• WaterWater onlyonly movesmoves throughthrough cellcell sap.sap.
•• EndodermisEndodermis cellscells controlcontrol thethe osmoticosmotic gradientgradient pullingpulling waterwater inin (with(with energyenergy andand transporttransport proteins)proteins) •• XylemXylem doesdoes thethe same:same: osmoticallyosmotically pullspulls waterwater intointo thethe rootroot xylem.xylem. Summary of Root to Leaf Water Movement •• ToTo getget waterwater toto thethe toptop ofof talltall plants….plants…. •• ItIt isis pulledpulled byby thethe evaporationevaporation ofof waterwater fromfrom thethe leavesleaves (like(like thethe pullpull generatedgenerated byby suckingsucking onon aa straw).straw). Transpiration and the Stomata •• TranspirationTranspiration (=(= evaporationevaporation ofof waterwater fromfrom leaves)leaves) pullspulls waterwater andand mineralsminerals upup stemsstems ANDAND providesprovides evaporativeevaporative cooling,cooling, butbut
•• ItIt resultsresults inin tremendoustremendous lossloss ofof waterwater,, whichwhich mustmust bebe controlled.controlled. Transpiration and the Stomata PlantsPlants managemanage costscosts andand benefitsbenefits (CO2(CO2 inin forfor photosynthesis,photosynthesis, H2OH2O out)out) with:with: •• EpidermisEpidermis –– FlatFlat cellscells coveredcovered byby aa waxywaxy waterproofwaterproof cuticlecuticle..
•• StomataStomata –– PoresPores thatthat letlet CO2CO2 inin andand H2OH2O outout whenwhen there’sthere’s notnot tootoo muchmuch waterwater stress.stress. TheseThese areare highlyhighly regulatedregulated byby thethe plantplant How do stomata work? •• TheThe stomastoma (or(or pore):pore): surroundedsurrounded byby twotwo guardguard cellscells
•• GuardGuard cellscells controlcontrol thethe openingopening andand closingclosing ofof thethe stomastoma thru…thru… changeschanges inin thethe guardguard cellcell waterwater potentialpotential Mechanism of stomatal opening
•• LightLight cuescues mostmost plantsplants toto openopen stomatastomata •• ActiveActive transporttransport ofof potassiumpotassium ionsions intointo thethe guardguard cells.cells. Fig 36.11 •• WhatWhat happenshappens toto thethe waterwater potentialpotential ofof thethe guardguard cells?cells? •• WhatWhat willwill happenhappen toto water?water? Mechanism of stomatal opening
•• H2OH2O movesmoves intointo thethe guardguard cellscells toto maintainmaintain osmoticosmotic balance.balance. •• StretchingStretching andand turgidityturgidity ofof thethe guardguard cells…..cells….. Fig •• StomataStomata openopen.. 36.11
•• (Closing(Closing isis thethe reversereverse startedstarted byby passivepassive diffusiondiffusion ofof potassiumpotassium outout ofof guardguard cells.)cells.) Regulation of stomatal opening
•• StomataStomata typicallytypically openopen inin thethe dayday (in(in responseresponse toto light)light) andand closeclose atat night.night.
ThisThis providesprovides CO2CO2 forfor photosynthesisphotosynthesis duringduring thethe day,day, butbut savessaves waterwater atat night.night. Signals for stomatal opening
•• AA lowlow levellevel ofof CO2CO2 inin thethe leafleaf constrainsconstrains photosynthesisphotosynthesis andand favorsfavors stomatalstomatal opening.opening. •• IfIf thethe plantplant isis tootoo dry:dry: mesophyllmesophyll cellscells releaserelease abscisicabscisic acidacid ÆÆ stomatastomata toto close.close.