1.Biofuels 2.Plant signaling (including neurobiology) 3.Climate/CO 2 change 4.Plant movements

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 potential Driving force = water's free energy = water potential  w Water moves to lower its 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 Negative pressure in xylem! 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 [solution] in equilibrium with cells

Water potential Measuring water potential  s (osmotic potential) is “easy” Measure [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 [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 [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

Water transport Therefore disagree about H 2 O transport in xylem Driving force = evaporation in leaves (evapotranspiration) Continuous H 2 O column from leaf to root draws up replacement H 2 O from soil (SPAC)

Water transport Driving force = evaporation in leaves (evapotranspiration) Continuous H 2 O column from leaf to root draws up replacement H 2 O Exact mech controversial

Water transport Driving force = evaporation in leaves (evapotranspiration) Continuous H 2 O column from leaf to root draws up replacement H 2 O Exact mech controversial Path starts at root hairs

Water transport Path starts at root hairs Must take water from soil

Water transport Path starts at root hairs Must take water from soil Ease depends on availability & how tightly it is bound

Water transport Path starts at root hairs Must take water from soil Ease depends on availability & how tightly it is bound Binding depends on particle size & chem

Water transport Must take water from soil Ease depends on availability & how tightly it is bound Binding depends on particle size & chem Availability depends on amount in soil pores

Water transport Availability depends on amount in soil pores Saturation: completely full

Water transport Availability depends on amount in soil pores Saturation: completely full Field capacity: amount left after gravity has drained excess

Water transport Availability depends on amount in soil pores Saturation: completely full Field capacity: amount left after gravity has drained excess Permanent wilting point: amount where soil water potential is too negative for plants to take it up

Water movement in plants Water enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis

Water movement in plants Water enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis Must enter endodermal cell

Water Transport Water enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis Must enter endodermal cell Why flooded plants wilt!

Water Transport Water enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis Must enter endodermal cell Why flooded plants wilt! Controls solutes

Water Transport Must enter endodermal cell Controls solutes Passes water & nutrients to xylem

Water Transport Passes water & nutrients to xylem  s of xylem makes root pressure

Water Transport Passes water & nutrients to xylem  s of xylem makes root pressure Causes guttation: pumping water into shoot

Water Transport Passes water & nutrients to xylem  s of xylem makes root pressure Causes guttation: pumping water into shoot Most water enters near root tips

Water Transport Most water enters near root tips Xylem is dead! Pipes for moving water from root to shoot

Water Transport Most water enters near root tips Xylem is dead! Pipes for moving water from root to shoot Most movement is bulk flow

Water Transport Xylem is dead! Pipes for moving water from root to shoot Most movement is bulk flow adhesion to cell wall helps

Water Transport Xylem is dead! Pipes for moving water from root to shoot Most movement is bulk flow adhesion to cell wall helps Especially if column is broken by cavitation (forms embolisms)

Water Transport Most movement is bulk flow adhesion to cell wall helps Especially if column broken by cavitation In leaf water passes to mesophyll

Water Transport Most movement is bulk flow adhesion to cell wall helps Especially if column broken by cavitation In leaf water passes to mesophyll, then to air via stomates

Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness

Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness ∆ H 2 O vapor pressure [H 2 O (g) ] & saturated H 2 O vapor pressure

Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness ∆ H 2 O vapor pressure [H 2 O (g) ] & saturated H 2 O vapor pressure saturated H 2 O vapor pressure varies with T, so RH depends on T

Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness ∆ H 2 O vapor pressure [H 2 O (g) ] & saturated H 2 O vapor pressure saturated H 2 O vapor pressure varies with T, so RH depends on T VPD is independent of T: says how fast plants lose H 2 O at any T

Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness Rate depends on pathway resistances

Water Transport Rate depends on pathway resistances stomatal resistance

Water Transport Rate depends on pathway resistances stomatal resistance Controlled by opening/closing

Water Transport Rate depends on pathway resistances stomatal resistance boundary layer resistance Influenced by leaf shape & wind