Post on 28-Dec-2015
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