Ions Lecture 4
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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
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
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
What drives low affinity K+ uptake through channels?
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
Where are genes encoding K+ channels expressed?
- stomatal guard cells
What is responsible for high affinity K+ uptake?
What drives calcium ion transport from apoplast to cytosol?
- large electrochemical-potential gradient
- inward-rectifying Ca2+ channels
What drives calcium ion transport from the cytosol to the apoplast?
Ca2+ ATPase (P-type)
What drives calcium ion transport from the cytosol to the vacuole?
- Ca2+ ATPase (P-Type)
- Ca2+-H+ antiporter
What drives calcium ion transport from the cytosol to the endoplasmic reticulum?
Ca2+ ATPase (P-Type)
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
What is transported using proton symporters?
- amino acids
what is transported using proton antiporters?
What happens under K deficiency?
starve plants for K+ - exhibit high affinity
What happens under S and P deficiencies?
- increase in number of carriers
- on resupply, number of carriers and vmax decrease
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