Lecture 8 Photoregulation

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Lecture 8Photoregulation

• Photosynthesis
• Light Quantity
• Photomorphogenesis
• Light Quality
• Photoperiodism
• Light Duration
• Phototropsim
• Light Direction

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Photoregulation

• Photosynthesis
• Photoreceptors
• Chlorophylls
• Carotenoids
• Regulation
• Photosynthetic Efficiency
• High Light
• Low Light
• Emerson Enhancement

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Light Quality

• Electromagnetic Spectrum
• Absorption Spectrum
• Action Spectrum

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Photoregulation

• Chloroplast
• Grana Lamellae
• Stroma Lamellae
• Stroma

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Thylakoid Complex Structure
CCII
CCI
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Photosynthetic Efficiency

• High Light
• Grana Unstacking
• High Red Far-Red Ratio (high red)
• Kinase
• Form PO4 bonds to LHCII
• LHCII particles separate
• Low Light
• Grana Stacking
• Low Red Far-Red Ratio (high far-red)
• Phosphatase
• Remove PO4
• LHCII particles bond together
• Emerson Enhancement Effect
• Far-Red induced increase in efficiency

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Light Quality

• Emerson Enhancement Effect

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Photomorphogenesis

• Light Quality
• Seed Germination
• Release from dormancy
• Weed seeds
• Red Light (5 sec) Induce Germination
• Far-Red (5 sec) Inhibit Germination
• R FR - Inhibit
• R FR R - Induce

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Seed Germination
Dark
5 Red
5 R 5 FR
R FR R
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Photomorphogenesis

• Seedling Development
• Etiolated
• Dark
• long, spindly, white (or yellow)
• De-Etiolated
• Light
• Red Light ( 5 sec pulse)
• short, thick, green
• R FR
• etiolated

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Seedling Development
Monocot Dark
Monocot Light
Dicot Light
Dicot Dark
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Deetiolation
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Photomorphogenesis

• Internode Elongation
• Shade Adapted (Shade Tolerant)
• No Response
• Shade Avoidance (Shade Sensitive)
• Low Red Far-Red Ratio
• Canopy Shade
• Rapid Elongation
• Escape Shade

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Shade Avoidance
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Photomorphogenesis

• Planting Density
• Nearest Neighbor Detection
• Reflected Far-Red Light
• Rapid Elongation
• Tall Plants - Center of dense plot
• Less Grain Yield
• More Vegetative Growth
• Short Plants - Edges of dense plot
• Less Dense Plot
• High Grain Yield
• Less Vegetative Growth

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Photoperiodism

• Daylength Perception
• Short-Day Plants
• Dark Period
• Longer than Critical Minimum
• 5 min Night Break
• Red - Inhibits Flowering
• Far-Red Promotes Flowering
• R FR R - No Flowering

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long day, short night
long day, short night
long day, short night
No flowers
short day, long night
short day, long night
short day, long night
flowers
white light
white light
white light
short day, interrupted night
short day, interrupted night
short day, interrupted night
No flowers
red light
red light
red light
No flowers
short day, red interruption
short day, red interruption
short day, red interruption
red
far-red
red
far-red
red
far-red
short day, red followed by far-red
short day, red followed by far-red
short day, red followed by far-red
flowers
Fig. 15-22, p. 253
Fig. 15-22, p. 253
Fig. 15-22, p. 253
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Photoperiodism

• Long-Day Plants
• Dark Period - Less than Critical Maximum
• Night Break - Not very effective
• End-Of-Day Far-Red
• 8 hr day 5 min R - No Flowering
• 8 hr day 5 min FR - Flowering
• 8 hr day FR R - No Flowering
• Daylength Extension
• Low Red Far-Red Ratio
• Like Shade Avoidance
• Promotes Flowering
• Not R/FR reversible

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Photoperiod

• Dormancy Release
• Buds
• Floral
• Vegetative
• Seeds
• Germination
• Flowering
• Long-Day Plants
• Short-Day Plants
• Dormancy Induction
• Growth Cessation
• Temperature Interaction

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Phototropism

• Directional Information
• Blue Light
• Stem Bending
• Toward Light
• Lateral Redistribution of Auxin
• Auxin High on Shaded Side
• Increased Growth
• Stomatal Opening
• Blue Light Activation of ATPase
• H ion extrusion
• K/Cl- Uptake
• H2O uptake
• Swelling of Guard Cells

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Phototropism
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Phototropism

• Leaf Movements
• Heliotropism - Legumes
• Pulvinus
• Similar to Stomatal Opening
• Multicellular
• H / K, Cl- exchange ---gt H2O uptake ---gt
  Swelling
• Dorsal lt---gt Ventral
• Dorsal swell ---gt Leaf moves down
• Ventral swell ---gt Leaf moves up

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Leaf Movements

• Pulvinus

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Leaf Movements
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Leaf Movements
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Phototropism

• Paraheliotropism
• parallel to light
• Soybeans
• Orthoheliotropism
• perpendicular to light
• Sunflower
• Solar Tracking

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Photoreceptors

• 1. Photosynthesis
• Chlorophylls
• Carotenoids
• Energy Transfer
• Light ----gt Chemical Energy
• 2. Photomorphogenesis Photoperiodism
• Red / Far-Red Reversible
• Phytochrome

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Phytochrome

• Dark Red Dark
• P -------gtPr ----------------gt Pfr ------gt
  Response lt---------------
• Far-Red
• Molecular Switch
• Pfr - Active Form

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Phytochrome Structure
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Phytochrome Absorption
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Phytochrome Genes

• 5 Phytochrome Genes
• 1. PhyA ------gt FR inhibition of Stem
  elongation (etiolated plants)
• -----gt FR promotion of flowering
• daylength extension
• 2. PhyB ------gt R inhibition of Stem
  elongation (etiolated plants)
• -----gt FR promotion of internode elongation
• shade avoidance

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Phytochrome Genes

• 3. PhyC ------gt ?
• 4. PhyD ------gt ?
• 5. PhyE ------gt ?
• Mechanism is still unclear

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Blue Light

• Cryptochrome
• Cry-1, Cry-2
• Bacterial Photolyases
• Hypocotyl Elongation (Cry-1)
• Flowering (Cry-2)
• Phototropin
• Phot-1, Phot-2
• Flavoproteins
• Hypocotyl Bending
• Carotenoid
• Stomatal Opening (?)

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Phototropism
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Blue Light Action Spectrum
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Phototropism

• Phototropin Mutant
• Flavoprotein
• LOV Domain Kinase
• 2 FMN Sites
• Plasma Membrane
• PHOT 1
• Low Light
• PHOT 2
• High Light

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Stomatal Opening
Light
DARK
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Blue Light Response
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Photoreceptor

• Carotenoid or Phototropin ?
• Evidence for Both
• Xanthophyll Cycle
• Violaxanthin
• Light Dark
• Zeaxanthin

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(No Transcript)
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UV Absorbing Pigment

• UV-B (280-320 nm)
• DNA
• Thymidine Dimers
• Chromosome Damage
• Unknown Photoreceptor
• UV-A (320-400 nm)
• Protein
• Photolyase
• DNA Repair
• Phototropin