Plan C We will pick a problem in plant biology and see where it takes us. Phytoremediation Plant products Biofuels Effects of seed spacing on seed germination Climate/CO2 change Stress responses/stress avoidance Improving food production Biotechnology Plant movements Plant signaling (including neurobiology) Flowering? Circadian rhythms Something else?

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 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!

pH Plants vary pH to control many processes! Plants alter pH @ roots to aid uptake

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: [H2O]: Ys (osmotic potential)

Water potential Water moves to lower its potential Depends on: [H2O]: Ys (osmotic potential) Pressure : Yp Turgor pressure inside cells

Water potential Water moves to lower its potential Depends on: [H2O]: Ys (osmotic potential) Pressure : Yp Turgor pressure inside cells Negative pressure in xylem!

Water potential Water moves to lower its potential Depends on: [H2O]: Ys (osmotic potential) Pressure Yp Gravity Yg Yw = Ys +Yp + Yg

Water potential Water moves to lower its potential Depends on: [H2O]: Ys (osmotic potential) Pressure Yp Gravity Yg Yw = Ys +Yp + Yg Yw of pure water at sea level & 1 atm = 0 MPA

Water potential Yw = Ys +Yp + Yg Yw of pure water at sea level & 1 atm = 0 MPA Ys (osmotic potential) is always negative

Water potential Yw = Ys +Yp + Yg Yw of pure water at sea level & 1 atm = 0 MPA Ys (osmotic potential) is always negative If increase [solutes] water will move in

Water potential Yw = Ys +Yp + Yg Yw of pure water at sea level & 1 atm = 0 MPA Ys (osmotic potential) is always negative If increase [solutes] water will move in Yp (pressure potential) can be positive or negative

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

Water potential Yp (pressure potential) can be positive or negative Usually positive in cells to counteract Ys Helps plants stay same size despite daily fluctuations in Yw

Water potential Yw = Ys +Yp + Yg Yp (pressure potential) can be positive or negative Usually positive in cells to counteract Ys Helps plants stay same size despite daily fluctuations in Yw Yp in xylem is negative, draws water upwards

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

Water potential Measuring water potential

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

Water potential Measuring water potential Ys (osmotic potential) is “easy” Measure concentration of solution in equilibrium with cells Yg (gravity potential) is easy: height above ground -0.01 Mpa/m

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

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

Measuring water potential YP (pressure potential) is hard! Pressure bomb = most common technique Others include pressure transducers, xylem probes Therefore disagree about H2O transport in xylem

Water transport Therefore disagree about H2O transport in xylem Driving force = evaporation in leaves (evapotranspiration) Continuous H2O column from leaf to root draws up replacement H2O from soil (SPAC)

Water transport Driving force = evaporation in leaves (evapotranspiration) Continuous H2O column from leaf to root draws up replacement H2O Exact mech controversial

Water transport Driving force = evaporation in leaves (evapotranspiration) Continuous H2O column from leaf to root draws up replacement H2O 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 Ys of xylem makes root pressure

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

Water Transport Passes water & nutrients to xylem Ys 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 ∆ H2O vapor pressure [H2O(g)] & saturated H2O vapor pressure

Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness ∆ H2O vapor pressure [H2O(g)] & saturated H2O vapor pressure saturated H2O 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 ∆ H2O vapor pressure [H2O(g)] & saturated H2O vapor pressure saturated H2O vapor pressure varies with T, so RH depends on T VPD is independent of T: says how fast plants lose H2O 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