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?????