Transcript Bio 226: Cell and Molecular Biology

1.
Biofuels
2. Plant signaling (including neurobiology)
3. Climate/CO2 change
4. Plant movements
WATER
• Plants' most important chemical
• most often limits productivity
Climate change will alter rainfall
Overall prediction is that crops will suffer in many parts of
world
WATER
• Plants' most important chemical
• most often limits productivity
• Often >90%% of a plant cell’s weight
• Gives cells shape
• Dissolves many chem
• most biochem is in water
• Source of e- for PS
WATER
•Constantly lose water due to PS
•Water transport is crucial!
• SPAC= Soil Plant Air Continuum
• moves from soil->plant->air
Properties of water
1) Cohesion = water H-bonded to water
2) Adhesion = water H-bonded to something else
• Cohesion and adhesion are crucial for water
movement in plants!
• Surface tension & adhesion in mesophyll creates
force that draws water through the plant!
Properties of water
1) Cohesion = water H-bonded to water
2) Adhesion = water H-bonded to something else
3) high specific heat
• absorb heat when break H-bonds
• Release heat when form H-bonds
Properties of water
1) Cohesion = water H-bonded to water
2) Adhesion = water H-bonded to something else
3) high specific heat
4) Ice floats
Properties of water
1) Cohesion = water H-bonded to water
2) Adhesion = water H-bonded to something else
3) high specific heat
4) Ice floats
5) Universal solvent
Properties of water
1) Cohesion = water H-bonded to water
2) Adhesion = water H-bonded to something else
3) high specific heat
4) Ice floats
5) Universal solvent
•Take up & transport
nutrients dissolved in
water
Properties of water
5) “Universal” solvent
•Take up & transport nutrients dissolved in water
•Transport organics dissolved in water
Properties of water
1) Cohesion = water H-bonded to water
2) Adhesion = water H-bonded to something else
3) high specific heat
4) Ice floats
5) Universal solvent
6) Hydrophobic interactions
Properties of water
1) Cohesion = water H-bonded to water
2) Adhesion = water H-bonded to something else
3) high specific heat
4) Ice floats
5) Universal solvent
6) Hydrophobic interactions
7) Water ionizes
pH
[H+] = acidity of a solution
pH = convenient way
to measure acidity
pH = - log10 [H+]
pH 7 is neutral:
[H+] = [OH-]
-> at pH 7 [H+]
= 10-7 moles/l
pH of cytoplasm = 7.2
pH of stroma & matrix
=8
pH of apoplast = 5.5
pH of lumen = 4.5
pH
Plants vary pH to control many processes!
Water movement
Diffusion: movement of single molecules down ∆[ ] due to
random motion until [ ] is even
Driving force?
Water movement
Diffusion: movement of single molecules down ∆[ ] due to
random motion until [ ] is even
Driving force: lowers free energy
∆G = ∆H- T∆S
Water movement
Diffusion: movement of single molecules down ∆[ ] due to
random motion until [ ] is even
Bulk Flow: movement of groups of
molecules down a pressure gradient
Water movement
Diffusion: movement of single molecules down ∆[ ] due to
random motion until [ ] is even
Bulk Flow: movement of groups of
molecules down a pressure gradient
• Independent of ∆ [ ] !
Water movement
Diffusion: movement of single molecules down ∆[] due to
random motion until [ ] is even
Bulk Flow: movement of groups of molecules down a
pressure gradient
•Independent of ∆[ ] !
•How water moves through xylem
Water movement
Diffusion: movement of single molecules down [] due to
random motion until [ ] is even
Bulk Flow: movement of groups of molecules down a
pressure gradient
•Independent of ∆ [ ] !
•How water moves through xylem
•How water moves through soil and apoplast
Water movement
Bulk Flow: movement of groups of molecules down a
pressure gradient
•Independent of ∆ [ ] !
•How water moves through xylem
•Main way water moves through soil and apoplast
•Very sensitive to radius of vessel: increases as r4
Water movement
Diffusion: movement of single molecules down ∆[] due to
random motion until [ ] is even
Bulk Flow: movement of groups of molecules down a
pressure gradient
•Independent of ∆[ ] !
•How water moves through xylem
•Main way water moves through soil and apoplast
•Very sensitive to radius of vessel: increases as r4
Osmosis: depends on bulk flow and diffusion!
Water movement
Osmosis: depends on bulk flow and diffusion!
water crosses membranes but other solutes do not
water tries to even its [ ] on each side
Water movement
Osmosis: depends on bulk flow and diffusion!
water crosses membranes but other solutes do not
water tries to even its [ ] on each side
other solutes can’t: result is net influx of water
Water movement
Osmosis: depends on bulk flow and diffusion!
•Moves through aquaporins, so rate depends on
pressure and [ ] gradients!
Water movement
Osmosis: depends on bulk flow and diffusion!
•Moves through aquaporins, so rate depends on
pressure and [ ] gradients!
• Driving force = water's free energy (J/m3 = MPa)
Water potential
Driving force = water's free energy
= water potential Yw
• Important for many aspects of
plant physiology
Water potential
Driving force = water's free energy = water potential Yw
Water moves to lower its potential
Water potential
Driving force = water's free energy = water potential Yw
Water moves to lower its potential
Water potential
Driving force = water's free energy = water potential Yw
Water moves to lower its potential
Depends on:
1. [H2O]: Ys (osmotic potential)
Water potential
Water moves to lower its potential
Depends on:
1. [H2O]: Ys (osmotic potential)
2. Pressure : Yp
• Turgor pressure inside cells
Water potential
Water moves to lower its potential
Depends on:
1. [H2O]: Ys (osmotic potential)
2. Pressure : Yp
• Turgor pressure inside cells
• Negative pressure in xylem!
Water potential
Water moves to lower its potential
Depends on:
1. [H2O]: Ys (osmotic potential)
2. Pressure Yp
3. Gravity Yg
Yw = Ys +Yp + Yg