Ions Lecture 4

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Ions Lecture 4
2011-12-01 17:02:45
PMB 135 exam6

plant physiology and biochemistry exam 6
Show Answers:

  1. How does a voltage-gated K+ channel in stomatal guard cell work?
    • 1) light goes on, H+-ATPase is activated and pumps protons out of the cell into the cell wall space
    • 2) creates a gradient of electrical potential across the membrane
    • 3) gate opens and postively charged K+ ions enter
    • 4) osmotic potential is lowered, turgor pressure builds up
    • 5) the stomate opens and water can enter

    • direction of K+ is unidirectional - channel is inward-rectifying
    • in stomatal closing - outward-rectifying
  2. Why does it matter that ions diffuse through a variety of channels?
    channels may open/close in response to voltage changes, changes in ion concentration, pH or phosphorylation

    the ion permeability depends on the mix of channels that are open at the time
  3. When do K+ ions go inward/outward through separate channels?
    • inward K+ channels:
    • accumulating K+ from environment
    • stomatal opening

    • outward K+ channels:
    • stomatal closing
    • release of K+ ions into xylem
  4. What drives low affinity K+ uptake through channels?
  5. Where is the K+ efflux and when does it occur?
    • on the plasma membrane
    • requires membrane potential to be more positive than equilibrium potential of K+ ions
  6. Where are genes encoding K+ channels expressed?
    • stomatal guard cells
    • roots
    • leaves
  7. What is responsible for high affinity K+ uptake?
    active symport
  8. What drives calcium ion transport from apoplast to cytosol?
    • large electrochemical-potential gradient
    • inward-rectifying Ca2+ channels
  9. What drives calcium ion transport from the cytosol to the apoplast?
    Ca2+ ATPase (P-type)
  10. What drives calcium ion transport from the cytosol to the vacuole?
    • Ca2+ ATPase (P-Type)
    • Ca2+-H+ antiporter
  11. What drives calcium ion transport from the cytosol to the endoplasmic reticulum?
    Ca2+ ATPase (P-Type)
  12. How is nitrate transported?
    • energy from symport with H+
    • strongly regulated according to nitrate availability
    • metabolism induced in presence of nitrate and uptake repressed if nitrate accumulates
  13. What is transported using proton symporters?
    • phosphate
    • sucrose
    • amino acids
    • nitrate
  14. what is transported using proton antiporters?
    • Ca2+
    • Na2+
  15. What happens under K deficiency?
    starve plants for K+ - exhibit high affinity
  16. What happens under S and P deficiencies?
    • increase in number of carriers
    • on resupply, number of carriers and vmax decrease