plant mineral nutrition: solute transport hort 301 – plant physiology september 22, 2010 taiz and...
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Plant Mineral Nutrition: Solute TransportHORT 301 – Plant Physiology
September 22, 2010Taiz and Zeiger - Chapter 6, Appendix 1
1.5 (A) The plasma membrane, endoplasmic reticulum, and other endosomes
Integral membrane transport proteins – responsible for movement of ions across membranes
Molecular diffusion - net movement of mineral nutrients and other molecules down the chemical potential gradient, passive transport
6.2 Development of a diffusion potential and a charge separation between two compartments
K+ > in B right and Cl- > in left, electrical gradient
K+ and Cl- move across membrane, concentration gradient
No net ion movement across membrane
Chemical potential gradient () – forces that drive diffusionMineral ions and charged molecules – concentration and electrical potential gradientsNeutral molecules – concentration gradient, unaffected by charge
APOPLASTpH 5.5
CYTOSOLpH 7.2
ΔE=-100 to -200 mV
PLASMAMEMBRANE
Membrane potential gradient (E) – electrical potential gradientDifferential ion accumulation on sides of the membrane
Inside negative membrane potential across the plasma membrane
Antiporter
6.14 Overview of the various transport processes on the plasma membrane and tonoplast (Part 2)
APOPLASTpH 5.5
CYTOSOLpH 7.2
ΔE=-100 to -200 mVPLASMAMEMBRANE
pH gradient - primarily responsible for the plasma membrane potential gradientpH gradient requires energyChemical energy (ATP hydrolysis) is coupled to H+-transport against the electrochemical gradient
ADP + Pi
ATP
ATP
ADP + Pi
H+
H+
pumps
H+
6.14 Overview of the various transport processes on the plasma membrane and tonoplast (Part 2)
APOPLASTpH 5.5
6.14 Overview of the various transport processes on the plasma membrane and tonoplast (Part 2)
Ion and solute transport across the plasma membrane coupled to ∆pH 6.14 Overview of the various transport processes on the plasma membrane and tonoplast (Part 2)
Translation of a membrane potential gradient into a force for diffusion∆E can drive diffusion of ions
At equilibrium – ion concentration gradient is balanced by the voltage difference
∆E (electrical potential/membrane potential) = 2.3RT/zF log Co/Ci
At equilibrium 2.3RT/zF = 59 mV, monovalent ion
∆E = 59 mV log Co/Ci
if Co/Ci = 10, log 10 = 1then ∆E = 59 mV x 1
An inside negative, membrane potential of -59 mV (~60 mV) can translate into a 10-fold concentration difference (monovalent cation)
Plasma membrane potential effects on a monovalent anion(e.g. Cl-), a membrane potential of -120 mV (inside negative) requires that [Cl-]apoplast must be >100X relative to [Cl-]cytosol for passive transport
Each ion has its own electrochemical potential
Specificity is due to unique concentration activity
Divalent (Ca2+ or SO42-) ions have 2X the electrical potential
6.4 Ion concentrations in the cytosol and the vacuole
pH 5.5
pH 7.2
- 100/ -200 mV
pH 5.5
+30 mV
Passive and active ion transport across the plasma membrane and tonoplast Dependent on concentration and membrane potential gradientIntracellular distribution of essential elements due to passive (dashed, -----) or active (solid line, →) transport
Transport protein categories – channels, carriers and pumps
Channels – diffusion inwards or outwards across the membrane
K+ channel
Primary active transport – energy production is coupled to ion transport H+ electrochemical gradients across the plasma membrane and tonoplast
Smith et al. (2010) Plant Biology
(pH 5.2) -100 to -200 mV
Apoplast Cytosol
Vacuolar H+-ATPase
ADP + Pi
ATP
H+
PM H+-ATPase
Secondary active transporters (carriers) – couple H+ transport to ion transportDown the H+ electrochemical gradientSymporter – same direction, antiporter – opposite directions
Model of H+-sucrose symporter function
Raven et al. (2005) Biology of Plants
H+-ATPase and H+-sucrose symporter coordination
Transport proteins at the plasma membrane
Smith et al. (2010) Plant Biology
pH 7.4-100 to -200 mV
pH 5.5
Tonoplast transport proteins
Smith et al. (2010) Plant Biology
pH 7.2
6.14 Overview of the various transport processes on the plasma membrane and tonoplast6.14 Overview of the various transport processes on the plasma membrane and tonoplast
+30 mV
Radial ion transport from soil solution to the xylem