Suggestions
1. Arabidopsis
3. Sorghum
2. Fast plant
4. Brachypodium
5. Amaranthus (C4 dicot) 6. Quinoa distachyon
7. Kalanchoe 8. Venus fly traps
9. C3 vs C4 Atriplex 10. C3 vs C4 Flaveria
11. C3 vs C4 Panicum
12. M. crystallinum C3-CAM
13. P. afra C3-CAM 14 . P. oleracea C4-CAM
Options
1. Pick several plants
•
C3, C4, CAM
•
Long Day, Short day, Day Neutral
•
Tropical, temperate, arctic
•
?????

Options
1. 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 1
1.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 H
2
O/CO
2
)

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

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

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

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

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

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

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

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

Y
P
Measuring water potential
(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

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
Y s of xylem makes root pressure

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

Water Transport
Passes water & nutrients to xylem
Y 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

Florigenic and antiflorigenic signaling pathways in Arabidopsis.
Matsoukas I G et al. Plant Cell Physiol 2012;53:1827-1842

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

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

Transition to Flowering
Can 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 l
)

Transition to Flowering
Can 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 l
)
•
FKF1/GI controlled by circadian clock

Transition to Flowering
Can 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 l
)
•
FKF1/GI controlled by circadian clock
•
PHYA & CRY also stabilize CO @ end of day

Transition to Flowering
Can be affected by daylength
Can 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 & makes
H3K27me3 -> silences gene

Transition to Flowering
Can be affected by daylength
Can 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 Flowering
Can be affected by daylength
Can 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 activates flowering @ high T by inducing FT mRNA
(ind of daylength)

Transition to Flowering
Can be affected by daylength
Can be affected by T
Can be affected by gibberellins (GA)

Gibberellins
Discovered 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

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

Gibberellins
Discovered 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 signaling
Used 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

Gibberellins
GAs 1, 3 & 4 are most bioactive
Act by triggering degradation of DELLA repressors

Gibberellins
GAs 1, 3 & 4 are most bioactive
Made at many locations in plant
Act by triggering degradation of DELLA repressors w/o GA DELLA binds & blocks activator (GRAS)

Gibberellins
Act by triggering degradation of DELLA repressors w/o GA DELLA binds & blocks activator bioactive GA binds GID1; GA-GID1 binds DELLA & marks for destruction

Gibberellins
Act by triggering degradation of DELLA repressors w/o GA DELLA binds & blocks activator bioactive GA binds GID1; GA-GID1 binds DELLA & marks for destruction
GA early genes are transcribed, start
GA responses

Transition to Flowering
Can 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 Flowering
Can 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 DELLA deg releasing SPL

Transition to Flowering
Can 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 Flowering
Can 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 Flowering
Can 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
Tomato terminating flower mutants
(tmf) flower early :
TMF coordinates transition to flowering

Transition to Flowering
Can be affected by nutrition
Pi deprivation induces miR399
Travels in phloem to repress PHO2, a neg regulator of Pi uptake

Transition to Flowering
Can be affected by nutrition
Pi deprivation induces miR399
Travels in phloem to repress PHO2, a neg regulator of Pi uptake miR399 enhances
TSF expression

Transition to Flowering
Can be affected by nutrition
Pi deprivation induces miR399
Travels in phloem to repress PHO2, a neg regulator of Pi uptake miR399 enhances
TSF expression
Sucrose enhances miR399 expression
(also many other genes)

Transition to Flowering
Can be affected by nutrition
Pi deprivation induces miR399
Travels in phloem to repress PHO2, a neg regulator of Pi uptake miR399 enhances
TSF expression
Sucrose enhances miR399 expression
(also many other genes) miR399 is Temp S!

http://www3.syngenta.com/global/e-licensing/en/elicensing/Catalog/Pages/Chemicallyinducedsucrosemetabolismtocontrolplantflowering.aspx