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