WATER Plants' most important chemical most often limits productivity

WATER Plants' most important chemical most often limits productivity Often >90% of a plant cell’s weight

WATER Plants' most important chemical most often limits productivity Often >90% of a plant cell’s weight Gives cells shape

WATER Plants' most important chemical most often limits productivity Often >90% of a plant cell’s weight Gives cells shape Dissolves many chem

WATER Dissolves many chem most biochem occurs in water Source of e - for PS

WATER most biochem occurs in water Source of e - for PS Constantly lose water due to PS (1000 H 2 O/CO 2 )

WATER most biochem occurs in water Source of e - for PS Constantly lose water due to PS Water transport is crucial!

WATER Water transport is crucial! SPAC= Soil Plant Air Continuum moves from soil->plant->air

Plant Water Uptake Water is drawn through plants along the SPAC, using its special properties to draw it from the soil into the air

WATER Formula = H 2 O Formula weight = 18 daltons Structure = tetrahedron, bond angle 104.5˚

WATER Structure = tetrahedron, bond angle 104.5˚ polar :O is more attractive to electrons than H  + on H  - on O

Water Polarity is reason for water’s properties water forms H-bonds with polar molecules

Water Polarity is reason for water’s properties water forms H-bonds with polar molecules Hydrophilic = polar molecules Hydrophobic = non-polar molecules

Properties of water 1)Cohesion = water H-bonded to water -> reason for surface tension

Properties of water 1)Cohesion = water H-bonded to water -> reason for surface tension -> why water can be drawn from roots to leaves

Properties of water 1) Cohesion = water H-bonded to water 2) Adhesion = water H-bonded to something else

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!

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: cools leaves

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 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 5) Universal solvent 6) Hydrophobic bonds 7) Water ionizes

pH [H + ] = acidity of a solution pH = convenient way to measure acidity pH = - log 10 [H + ] pH 7 is neutral: [H+] = [OH-] -> at pH 7 [H+] = moles/l

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 r 4

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 r 4 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/m 3 = MPa)

Water potential Driving force = water's free energy = water potential  w Important for many aspects of plant physiology

Water potential Driving force = water's free energy = water potential  w Water moves to lower its potential

Water potential Driving force = water's free energy = water potential  w Water moves to lower its potential

Water potential Driving force = water's free energy = water potential  w Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential)

Water potential Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential) 2.Pressure :  p Turgor pressure inside cells

Water potential Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential) 2.Pressure :  p Turgor pressure inside cells Negative pressure in xylem!

Water potential Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential) 2.Pressure  p 3.Gravity  g  w =  s +  p +  g

Water potential Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential) 2.Pressure  p 3.Gravity  g  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA

Water potential  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA  s (osmotic potential) is always negative

Water potential  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA  s (osmotic potential) is always negative If increase [solutes] water will move in

Water potential  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA  s (osmotic potential) is always negative If increase [solutes] water will move in  p (pressure potential) can be positive or negative

Water potential  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA  s (osmotic potential) is always negative If increase [solutes] water will move in  p (pressure potential) can be positive or negative Usually positive in cells to counteract  s

Water potential  p (pressure potential) can be positive or negative Usually positive in cells to counteract  s Helps plants stay same size despite daily fluctuations in  w

Water potential  w =  s +  p +  g  p (pressure potential) can be positive or negative Usually positive in cells to counteract  s Helps plants stay same size despite daily fluctuations in  w  p in xylem is negative, draws water upwards

Water potential  w =  s +  p +  g  p (pressure potential) can be positive or negative Usually positive in cells to counteract  s Helps plants stay same size despite daily fluctuations in  w  p in xylem is negative, draws water upwards  g can usually be ignored, but important for tall trees

Water potential Measuring water potential

Water potential Measuring water potential  s (osmotic potential) is “easy” Measure concentration of solution in equilibrium with cells

Water potential Measuring water potential  s (osmotic potential) is “easy” Measure concentration of solution in equilibrium with cells  g (gravity potential) is easy: height above ground Mpa/m

Water potential Measuring water potential  s (osmotic potential) is “easy” Measure concentration of solution in equilibrium with cells  g (gravity potential) is easy: height above ground  P (pressure potential) is hard! Pressure bomb = most common technique

Water potential Measuring water potential  s (osmotic potential) is “easy” Measure concentration of solution in equilibrium with cells  g (gravity potential) is easy: height above ground  P (pressure potential) is hard! Pressure bomb = most common technique Others include pressure transducers, xylem probes

Measuring water potential  P (pressure potential) is hard! Pressure bomb = most common technique Others include pressure transducers, xylem probes Therefore disagree about H 2 O transport in xylem