Transport in PlantsTransport in Plants

Chapter 36Chapter 36

Cellular TransportCellular Transport

A. passive transportA. passive transport Driven by the principles of diffusionDriven by the principles of diffusion Much of the diffusion is facilitatedMuch of the diffusion is facilitated Selective channels are usually gated and regulatedSelective channels are usually gated and regulated

Cellular TransportCellular Transport

B. Active TransportB. Active Transport Often uses proton pumpOften uses proton pump

Generates membrane potentialGenerates membrane potential may be used to drive active transport of other may be used to drive active transport of other

molecules (cotransport)molecules (cotransport)

Cellular TransportCellular Transport

Water TransportWater Transport By osmosis water moves from hypotonic to By osmosis water moves from hypotonic to

hypertonic solution in cellshypertonic solution in cells BUT in plant cell, cell wall provides a pressure BUT in plant cell, cell wall provides a pressure

component, therefore water potential must be usedcomponent, therefore water potential must be used

Water potential review:Water potential review:

What is What is ψψ of a container of distilled water that of a container of distilled water that is open?is open?

If If ψψ inside a cell is -0.7 MPa, and outside of inside a cell is -0.7 MPa, and outside of the cell is -0.1 MPa, which direction will water the cell is -0.1 MPa, which direction will water move?move?

If If ψψSS=-0.5MPa and =-0.5MPa and ψψPP=0.1MPa, will water =0.1MPa, will water

move into or out of this cell if it is placed in an move into or out of this cell if it is placed in an environment where environment where ψψ=-0.2 MPa? =-0.2 MPa?

AquaporinsAquaporins

1990’s Peter Agre (John’s Hopkins) discovers 1990’s Peter Agre (John’s Hopkins) discovers water pores in membranes that facilitate water pores in membranes that facilitate diffusion of waterdiffusion of water 2003 Nobel Prize in Chemistry along with 2003 Nobel Prize in Chemistry along with

Roderick MacKinnonRoderick MacKinnon Water is small and can diffuse through bilayer Water is small and can diffuse through bilayer

to some extent despite polarityto some extent despite polarity Aquaporins speed up this diffusionAquaporins speed up this diffusion May be gated to regulate water diffusionMay be gated to regulate water diffusion

3 Cellular Compartments3 Cellular Compartments

Apoplast: continuum of Apoplast: continuum of cell walls and cell walls and extracellular spacesextracellular spaces

Symplast: continuum of Symplast: continuum of cytosol linked by cytosol linked by plasmodesmataplasmodesmata

Vacuole: bound by Vacuole: bound by membrane called membrane called tonoplasttonoplast

Lateral TransportLateral Transport

Short distance horizontal movementShort distance horizontal movement MechanismsMechanisms

Transmembrane (through membranes from one Transmembrane (through membranes from one cell to the next) – slowcell to the next) – slow

Symplastic (through one membrane into cell, then Symplastic (through one membrane into cell, then through plasmodesmata)through plasmodesmata)

Apoplastic (through cell walls)Apoplastic (through cell walls)

Absorption by RootsAbsorption by Roots

Root hairs increase surface areaRoot hairs increase surface area Mycorrhizae (fungal partners) enhance Mycorrhizae (fungal partners) enhance

absorptionabsorption Endodermis functions as selective regionEndodermis functions as selective region

Symplastic continues through plasmodesmataSymplastic continues through plasmodesmata Apoplastic must cross plasma membrane into Apoplastic must cross plasma membrane into

cytosol due to Casparian stripcytosol due to Casparian strip Casparian strip is waxy and hydrophobic, traps Casparian strip is waxy and hydrophobic, traps

water and minerals in the vascular tissuewater and minerals in the vascular tissue

Long Distance Transport in the Long Distance Transport in the XylemXylem

Root Pressure: PushingRoot Pressure: Pushing Transpiration: PullingTranspiration: Pulling

Root PressureRoot Pressure

Used by some plants, at nightUsed by some plants, at night At night, plants still expend energy pumping At night, plants still expend energy pumping

minerals into xylemminerals into xylem Accumulation of nutrients decreases Accumulation of nutrients decreases ψψ , ,

causing water to flow in by osmosiscausing water to flow in by osmosis This upward push is root pressureThis upward push is root pressure Guttation: exudation of water droplets seen in Guttation: exudation of water droplets seen in

the morningthe morning

TranspirationTranspiration

Major mechanism of movementMajor mechanism of movement Water is adhesive and cohesiveWater is adhesive and cohesive As one water droplet moves, the next also As one water droplet moves, the next also

moves (water in continuous column in xylem)moves (water in continuous column in xylem) As water evaporates out of the stomata, water As water evaporates out of the stomata, water

below moves upwardbelow moves upward

Guard CellsGuard Cells

Guard cells regulate water loss.Guard cells regulate water loss. What conditions will promote the closing of What conditions will promote the closing of

guard cells?guard cells? Buckle outward when turgid Buckle outward when turgid Regulate opening and closing by managing KRegulate opening and closing by managing K++

StomataStomata

Guard CellsGuard Cells

Pump HPump H++ out, K out, K++ enters due to electric charge, water enters due to electric charge, water follows due to osmosisfollows due to osmosis

Close when KClose when K++ leaves (water follows) leaves (water follows) Aquaporins may vary permeability to regulateAquaporins may vary permeability to regulate

Some leaf molds, which are fungi that Some leaf molds, which are fungi that parasitize plants, secrete a chemical that parasitize plants, secrete a chemical that causes guard cells to accumulate potassium causes guard cells to accumulate potassium ions. How does this adaptation enable the leaf ions. How does this adaptation enable the leaf mold to infect the plant? mold to infect the plant?

Guard Cell CuesGuard Cell Cues

Light stimulates a blue light receptor in guard Light stimulates a blue light receptor in guard cells, activates Hcells, activates H++ pumps pumps

COCO22 depletion when Calvin cycle starts depletion when Calvin cycle starts Can trick guard cells by placing in environment Can trick guard cells by placing in environment

without COwithout CO22

Internal Clock Internal Clock Open and close even in 24 hour darkOpen and close even in 24 hour dark Circadian rhythmCircadian rhythm

What adaptations are seen for arid What adaptations are seen for arid climates?climates?

thick leaves (low SA/vol)thick leaves (low SA/vol) Thick cuticleThick cuticle Stomata on lower leaf surfaceStomata on lower leaf surface Stomata in pores to shield wind Shed leaves in hot dry seasonShed leaves in hot dry season Cacti have no leaves (adapt to spines) CAM photosynthesisCAM photosynthesis

Phloem TransportPhloem Transport

TranslocationTranslocation Sugar source to sugar sinkSugar source to sugar sink Sugar loaded into sieve tube members by active Sugar loaded into sieve tube members by active

transporttransport Water follows by osmosis (increases pressure)Water follows by osmosis (increases pressure) At sink, sugar leaves sieve tube members (by At sink, sugar leaves sieve tube members (by

diffusion or active transport)diffusion or active transport) Water follows (decreases pressure)Water follows (decreases pressure) Water is recycled by xylemWater is recycled by xylem

Oleander: stomata in “cypts”

Old Man cactus