transport in vascular plants overview of transport mechanisms absorption of water and minerals by...
TRANSCRIPT
Transport in Vascular Plants
Overview of Transport MechanismsAbsorption of Water and
Minerals by RootsTransport of Xylem SapThe Control of TranspirationTranslocation of Phloem Sap
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
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
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
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
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
Xerophytes-Special Adaptations• “desert” plants• Thick cuticle• Small leaves, sometimes needles• Store water• Stomates in pits• Fewer stomates• CAM plants• C4 plants
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?????