Plant Transport

• Transport in Plants
  • Water and minerals
  • Transport in xylem
  • Transpiration
    • Evaporation, adhesion, and cohesion
    • Negative pressure
  • Sugars
  • Transport in phloem
  • Bulk flow
    • Calvin cycle in leaves loads sucrose in phloem
    • Positive pressure
  • Gas Exchange
  • Photosynthesis
    • CO2 in; O2 out
    • Stomates
  • Respiration
    • O2 in; CO2 out
    • Roots exchange gases within air spaces in soil
• Water and Mineral Absorption
  • Water absorption from soil
  • Osmosis
  • Aquaporins
  • Mineral absorption
  • Active transport
  • Proton pumps
    • Active transport of H+
• Mineral Absorption
  • Proton pumps
  • Active transport of H+ ions out of cell
    • Chemiosmosis
    • H+ gradient
  • Creates membrane potential
    • Difference in charge
    • Drives cation uptake
  • Creates gradient
    • Co-transport of other solutes against their gradient
• Water Flow Through Root
  • Porous cell wall
  • Water can flow through cell wall route and not enter cells
  • Plant needs to force water into cells
• Controlling the Route of Water in Root
  • Endodermis
  • Cell layer surrounding vascular cylinder of root
  • Lined with impermeable Casparian strip
  • Forces fluid through selective cell membrane
    • Filtered and forced through xylem cells
• Mycorrhizae Increase Absorption
  • Symbiotic relationship between fungi and plant
  • Symbiotic fungi greatly increase surface area for absorption of water and minerals
  • Increases volume of soil reached by plant
  • Increases transport to hist plant
• Transport of Sugars in Phloem
  • Loading of sucrose into phloem
  • Flow through cells via plasmodesmata
  • Proton pumps
    • Cotransport of sucrose into cells down proton gradient
• Pressure Flow in Phloem
  • Mass flow hypothesis
  • “Source to sink” flow
    • Direction of transport in phloem is dependent on plant’s needs
  • Phloem loading
    • Active transport of sucrose into phloem
    • Increased sucrose concentration decreases H2O potential
  • Water flows in from xylem cells
    • Increase in pressure due to increase in H2O causes flow
• Experimentation
  • Testing pressure flow hypothesis
  • Using aphids to measure sap flow and sugar concentration along plant system

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