transport in vascular plants overview of transport mechanisms absorption of water and minerals by...
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Transport in Vascular Plants
Overview of Transport MechanismsAbsorption of Water and
Minerals by RootsTransport of Xylem SapThe Control of TranspirationTranslocation of Phloem Sap
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Overview
At the cellular level: active and passive transport
Proton pumps-move H+ out of cell, creates electrochemical gradient and pulls + ions into the cell
Role of water potential and osmosis Role of aquaporins Symplast and apoplast pathways
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Absorption of Water and Minerals SoilEpidermisRoot CortexXylem Soil epidermis-root hairs, mycorrhizae Epidermisto root cortex-combination of
apoplastic and symplastic routes Root cortex xylem-apoplastic route
blocked by Casparian strip surrounding endodermis, minerals and ions must go through symplastic route
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Transport of Xylem Sap
Depends upon transpiration and physical properties of water
15 m/hr or faster Root pressure pushes, limited TACT forces (transpiration, adhesion,
cohesion and tension) Bulk flow, movement of fluid due to
pressure differences at opposite ends of the conduit
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The Control of Transpiration• Role of Guard Cells-regulate
transpiration rate• Benefits of transpiration-mineral
transfer, evaporative cooling• Problems created by transpiration-
excess water loss• Regulation of guard cells balances
the benefits and problems
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Guard Cell Regulation
Size of cells change in response to water flow in or out
Osmotic changes initiated by manipulating K+ concentrations. K+ in water comes in, increased turgor, cell size increase, K+ out….
[K+] probably regulated by proton pumps responding to light and blue light receptors
Abcissic acid (plant hormone) can override system when excess transpiration occurs
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Xerophytes-Special Adaptations• “desert” plants• Thick cuticle• Small leaves, sometimes needles• Store water• Stomates in pits• Fewer stomates• CAM plants• C4 plants
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Phloem Function
Translocation Sugar produced at source (leaf), unloaded into
sink (roots, stems, fruit) Active transport moves sugar into system by
proton pumps creating an H+ gradient and subsequent cotransport of sucrose.
Utilizes both symplastic and apoplastic routes One meter/hour Pressure flow moves material through the tubes
(hydrostatic pressure) Aphids have been used to study this process?????
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