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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?
H+-ATPase
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
roots
leaves
What is responsible for high affinity K+ uptake?
active symport
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?
phosphate
sucrose
amino acids
nitrate
what is transported using proton antiporters?
Ca2+
Na2+
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
Author
cornpops
ID
119416
Card Set
Ions Lecture 4
Description
plant physiology and biochemistry exam 6
Updated
12/1/2011, 10:02:45 PM
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