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 Constantly lose water due to PS (1000 H 2 O/CO 2 fixed) Water transport is crucial! SPAC= Soil Plant Air Continuum moves from soil->plant->air

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 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 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

Measuring water potential 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)

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

Measuring water potential 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

Measuring water potential Path starts at root hairs Must take water from soil

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

Measuring water potential 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

Measuring water potential 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

Measuring water potential Availability depends on amount in soil pores Saturation: completely full

Measuring water potential Availability depends on amount in soil pores Saturation: completely full Field capacity: amount left after gravity has drained excess

Measuring water potential 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

Processes affected by pCO 2 1)Pathways that use CO 2 as substrate Calvin cycle (Carbon reduction pathway)

Processes affected by pCO 2 1)Pathways that use CO 2 as substrate Calvin cycle (Carbon reduction pathway)

Processes affected by pCO 2 Calvin cycle (Carbon reduction pathway) 1)RuBP binds CO 2 2) rapidly splits into two 3-Phosphoglycerate therefore called C3 photosynthesis

Processes affected by pCO 2 Calvin cycle (Carbon reduction pathway) 1)RuBP binds CO 2 2) rapidly splits into two 3-Phosphoglycerate 3) catalyzed by Rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase) the most important & abundant protein on earth Lousy K m Rotten V max !

Processes affected by pCO 2 Calvin cycle (Carbon reduction pathway) Reversing glycolysis converts 3-Phosphoglycerate to G3P consumes 12 ATP & 12 NADPH/glucose

Processes affected by pCO 2 Calvin cycle (Carbon reduction pathway) Reversing glycolysis G3P has 2 possible fates 1) 1 in 6 becomes (CH 2 O) n 2) 5 in 6 regenerate RuBP

Processes affected by pCO 2 5 in 6 G3P regenerate RuBP Basic problem: converting a 3C to a 5C compound feed in five 3C sugars, recover three 5C sugars

Regenerating RuBP Basic problem: converting a 3C to a 5C compound must assemble intermediates that can be broken into 5 C sugars after adding 3C subunit

Processes affected by pCO 2 1)Pathways that use CO 2 as substrate Calvin cycle (Carbon reduction pathway) Rubisco must be carbamylated & bind Mg 2+ to be active!

Processes affected by pCO 2 1)Pathways that use CO 2 as substrate Calvin cycle (Carbon reduction pathway) Rubisco must be carbamylated & bind Mg 2+ to be active! RuBP binds & inactivates uncarbamylated rubisco

Processes affected by pCO 2 1)Pathways that use CO 2 as substrate Calvin cycle (Carbon reduction pathway) Rubisco must be carbamylated & bind Mg 2+ to be active! RuBP binds & inactivates uncarbamylated rubisco Rubisco activase removes this RuBP (also CA1P)