Suggestions1. Arabidopsis 2. Fast plant3. Sorghum 4. Brachypodium distachyon5. Amaranthus (C4 dicot)6. Quinoa7. Kalanchoe 8. Venus fly traps9. C3 vs C4 Atriplex 10. C3 vs C4 Flaveria11. C3 vs C4 Panicum 12. M. crystallinum C3-CAM13. P. afra C3-CAM 14 . P. oleracea C4-CAM

Options•Pick several plants• C3, C4, CAM• Long Day, Short day, Day Neutral• Tropical, temperate, arctic• ?????

Options1.Pick several plants• C3, C4, CAM• Long Day, short day, Day neutral• Tropical, temperate, arctic• ?????

2.Pick one plant• Study many conditions• Study many variants/mutants• ?????

Grading?Combination of papers, presentations & lab reports• 4 lab reports @ 2.5 points each• 5 assignments @ 2 points each• Presentation on global change and plants: 5 points • Research proposal: 10 points • Final presentation: 15 points • Poster: 10 points• Draft report 10 points• Final report: 30 points

Assignment 11.Pick a plant that might be worth studying•Try to convince the group in 5-10 minutes why yours is best: i.e., what is known/what isn’t known

WATER• Plants' most important chemical• most often limits productivity

•Gives cells shape• Dissolves many chem: most biochem occurs in water•Constantly lose water due to PS (1000 H2O/CO2)

Plant Water Uptake

Water is drawn through plants along the SPAC, relying on adhesion & cohesion (&surface tension) to draw water from the soil into the air

Drawn through plant by cohesion & adhesionSurface tension & adhesion in mesophyll creates force that draws water through the plant!

Water potentialWater moves to lower its potentialDepends on:• [H2O]: s (osmotic potential)

• Pressure p

• Gravity g

w = s +p + g

Water potentialw = 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 upwardsg can usually be ignored, but important for tall trees

Water potentialMeasuring water potentials (osmotic potential) is “easy”• Measure concentration of solution in equilibrium with

cells

Water potentialMeasuring water potentials (osmotic potential) is “easy”• Measure concentration of solution in equilibrium with

cells g (gravity potential) is easy: height above ground• -0.01 Mpa/m

Water potentialMeasuring water potentials (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 potentialMeasuring water potentials (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 techniqueOthers include pressure transducers, xylem probes

Measuring water potentialP (pressure potential) is hard!• Pressure bomb = most common techniqueOthers include pressure transducers, xylem probesTherefore disagree about H2Otransport in xylem

Water transportTherefore disagree about H2Otransport in xylem• Driving force = evaporation in leaves (evapotranspiration) • Continuous H2O column from leaf to root draws up replacement H2O from soil (SPAC)

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

Water transportDriving force = evaporation in leaves

(evapotranspiration)• Continuous H2O column from leaf to root draws up replacement H2O • Exact mech controversialPath starts at root hairs

Water transportPath starts at root hairs• Must take water from soil

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

Measuring water potentialPath 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 potentialMust 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 potentialAvailability depends on amount in soil pores• Saturation: completely full

Measuring water potentialAvailability depends on amount in soil pores• Saturation: completely full• Field capacity: amount left after gravity has drained

excess

Measuring water potentialAvailability 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 plantsWater enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis

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

Water TransportWater enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermisMust enter endodermal cellWhy flooded plants wilt!

Water TransportWater enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermisMust enter endodermal cellWhy flooded plants wilt!Controls solutes

Water TransportMust enter endodermal cellControls solutesPasses water & nutrients to xylem

Water TransportPasses water & nutrients to xylems of xylem makes root pressure

Water TransportPasses water & nutrients to xylems of xylem makes root pressure

Causes guttation: pumping water into shoot

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

Causes guttation: pumping water into shootMost water enters near root tips

Water TransportMost water enters near root tipsXylem is dead! Pipes for moving water from root to shoot

Water TransportMost water enters near root tipsXylem is dead! Pipes for moving water from root to shootMost movement is bulk flow

Water TransportXylem is dead! Pipes for moving water from root to shootMost movement is bulk flow• adhesion to cell wall helps

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

Water TransportMost movement is bulk flow• adhesion to cell wall helps•Especially if column broken by cavitationIn leaf water passes to mesophyll

Water TransportMost movement is bulk flow• adhesion to cell wall helps•Especially if column broken by cavitationIn leaf water passes to mesophyll, then to air via stomates

Water TransportIn leaf water passes to mesophyll, then to air via stomatesDriving force = vapor pressure deficit (VPD)• air dryness

Water TransportIn leaf water passes to mesophyll, then to air via stomatesDriving force = vapor pressure deficit (VPD)• air dryness•∆ H2O vapor pressure [H2O(g)]& saturated H2O vapor pressure

Water TransportIn leaf water passes to mesophyll, then to air via stomatesDriving force = vapor pressure deficit (VPD)• air dryness•∆ H2O vapor pressure [H2O(g)]& saturated H2O vapor pressure• saturated H2O vapor pressurevaries with T, so RH depends on T

Water TransportIn leaf water passes to mesophyll, then to air via stomatesDriving force = vapor pressure deficit (VPD)• air dryness•∆ H2O vapor pressure [H2O(g)]& saturated H2O vapor pressure• saturated H2O vapor pressurevaries with T, so RH depends on T• VPD is independent of T: says how fast plants lose H2O at any T

Water TransportIn leaf water passes to mesophyll, then to air via stomatesDriving force = vapor pressure deficit (VPD)• air drynessRate 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 TransportRate depends on pathway resistances• stomatal resistance• boundary layer resistance• Influenced by leaf shape & wind

Florigenic and antiflorigenic signaling pathways in Arabidopsis.

Matsoukas I G et al. Plant Cell Physiol 2012;53:1827-1842

Transition to FloweringAdults are competent to flower, but need correct signalsVery complex process!Can be affected by:• Daylength• Temperature (especially cold!)• Water stress• Nutrition• Hormones• Age

Transition to FloweringCan be affected by daylength (photoperiodic pathway)• Mainly through CO protein stability

Transition to FloweringCan be affected by daylength (photoperiodic pathway)• Mainly through CO protein stability• FKF1/GI bind CO & remove FT & CO inhibitor CDF

in afternoon (controlled by clock & enhanced by blue )

Transition to FloweringCan be affected by daylength (photoperiodic pathway)• Mainly through CO protein stability• FKF1/GI bind CO & remove FT & CO inhibitor CDF

in afternoon (controlled by clock & enhanced by blue )• FKF1/GI controlled by circadian clock

Transition to FloweringCan be affected by daylength• Mainly through CO protein stability• FKF1/GI bind CO & remove FT & CO inhibitor CDF

in afternoon (controlled by clock & enhanced by blue )• FKF1/GI controlled by circadian clock• PHYA & CRYalso stabilize CO @end of day

Transition to FloweringCan be affected by daylengthCan be affected by T• FLC blocks flowering in fall; after 20 days near 0˚C

plants make COLDAIR ncRNA

FLC blocks flowering in fall; after 20 days near 0˚C plants make COLDAIR ncRNA: Targets Polycomb Repressor Complex 2 to FLC locus & makesH3K27me3 ->silences gene

Transition to FloweringCan be affected by daylengthCan be affected by T• FLC blocks flowering in fall; after 20 days near 0˚C

plants make COLDAIR ncRNA ->PRC2 silences FLC• Can then flower next spring

Transition to FloweringCan be affected by daylengthCan be affected by T• FLC blocks flowering in fall; after 20 days near 0˚C

plants make COLDAIR ncRNA ->PRC2 silences FLC• Can then flower next spring• PIF4 activatesflowering @ high Tby inducing FT mRNA(ind of daylength)

Transition to FloweringCan be affected by daylengthCan be affected by TCan be affected by gibberellins (GA)

GibberellinsDiscovered by studying "foolish seedling" disease in rice• Kurosawa (1926): fungal filtrate causes these effects• Yabuta (1935): purified gibberellins from filtrates of Gibberella fujikuroi cultures • Discovered in plants in 1950s

GibberellinsDiscovered in plants in 1950s• "rescued" some dwarf corn & pea mutants• Made rosette plants bolt

GibberellinsDiscovered in plants in 1950s• "rescued" some dwarf corn & pea mutants• Made rosette plants bolt• Trigger adulthood in ivy & conifers

Gibberellins• "rescued" some dwarf corn & pea mutants• Made rosette plants bolt• Trigger adulthood in ivy & conifers• Induce growth of seedless fruit• Promote seed germination

Gibberellins• "rescued" some dwarf corn & pea mutants• Made rosette plants bolt• Trigger adulthood in ivy & conifers• Promote seed germination• >136 gibberellins (based on structure)!

Gibberellins>136 gibberellins (based on structure)!• Most plants have >10• Activity varies dramatically!

Gibberellins>136 gibberellins (based on structure)!• Most plants have >10• Activity varies dramatically!• Most are precursors or degradation products• GAs 1, 3 & 4 are most bioactive

Gibberellin signalingUsed mutants to learn about GA signaling•Many are involved in GA synthesis•Varies during development

•Others hit GA signaling•Gid = GA insensitive• encode GA receptors•Sly = E3 receptors•DELLA (eg rga) = repressors of GA signaling

GibberellinsGAs 1, 3 & 4 are most bioactiveAct by triggering degradationof DELLA repressors

GibberellinsGAs 1, 3 & 4 are most bioactiveMade at many locations in plantAct by triggering degradationof DELLA repressorsw/o GA DELLA binds & blocks activator (GRAS)

GibberellinsAct by triggering degradation of DELLA repressorsw/o GA DELLA binds & blocks activatorbioactive GA binds GID1; GA-GID1 binds DELLA & marks for

destruction

GibberellinsAct by triggering degradation of DELLA repressorsw/o GA DELLA binds & blocks activatorbioactive GA binds GID1; GA-GID1 binds DELLA & marks for

destructionGA early genes are transcribed, start GA responses

Transition to FloweringCan be affected by gibberellins (GA)DELLA bind microRNA156 (miR156)-targeted SPL

transcription factors, which promote flowering by activating miR172 and MADS box genes

Transition to FloweringCan be affected by gibberellins (GA)DELLA bind microRNA156 (miR156)-targeted SPL

transcription factors, which promote flowering by activating miR172 and MADS box genes

GA triggers DELLAdeg releasing SPL

Transition to FloweringCan be affected by age (autonomous pathway)In young plants, SPL synthesis is blocked by high levels of

miRNA156 : delays juvenile -> adult (OE delays it more)

Transition to FloweringCan be affected by age (autonomous pathway)In young plants, SPL synthesis is blocked by high levels of

miR156 : delays juvenile -> adult miR156 levels decay with age independently of other cues->let SPL act

Transition to FloweringCan be affected by age (autonomous pathway)In young plants, SPL synthesis is blocked by high levels of

miR156 : delays juvenile -> adultmiR156 levels decay with age independently of other cues->let SPL actTomato terminating flower mutants(tmf) flower early :TMF coordinatestransition to flowering

Transition to FloweringCan be affected by nutritionPi deprivation induces miR399Travels in phloem to repress PHO2, a neg regulator of Pi

uptake

Transition to FloweringCan be affected by nutritionPi deprivation induces miR399Travels in phloem to repress PHO2, a neg regulator of Pi

uptakemiR399 enhances TSF expression

Transition to FloweringCan be affected by nutritionPi deprivation induces miR399Travels in phloem to repress PHO2, a neg regulator of Pi

uptakemiR399 enhances TSF expressionSucrose enhancesmiR399 expression(also many other genes)

Transition to FloweringCan be affected by nutritionPi deprivation induces miR399Travels in phloem to repress PHO2, a neg regulator of Pi

uptakemiR399 enhances TSF expressionSucrose enhancesmiR399 expression(also many other genes)miR399 is Temp S!

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