Transport in plant2

Transport in Vascular Plants
Overview of Transport Mechanisms
Absorption of Water and Minerals by Roots
Transport of Xylem Sap
The Control of Transpiration
Translocation 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
SoilEpidermisRoot CortexXylem
Soil epidermis-root hairs, mycorrhizae
Epidermisto 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?????