Ions Lecture 4

• 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

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

• inward K+ channels:
• accumulating K+ from environment
• stomatal opening

• outward K+ channels:
• stomatal closing
• release of K+ ions into xylem

H+-ATPase

• on the plasma membrane
• requires membrane potential to be more positive than equilibrium potential of K+ ions

• stomatal guard cells
• roots
• leaves

active symport

• large electrochemical-potential gradient
• inward-rectifying Ca2+ channels

Ca2+ ATPase (P-type)

• Ca2+ ATPase (P-Type)
• Ca2+-H+ antiporter

Ca2+ ATPase (P-Type)

• energy from symport with H+
• strongly regulated according to nitrate availability
• metabolism induced in presence of nitrate and uptake repressed if nitrate accumulates

• phosphate
• sucrose
• amino acids
• nitrate

• Ca2+
• Na2+

starve plants for K+ - exhibit high affinity

• increase in number of carriers
• on resupply, number of carriers and vmax decrease