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Plant Growth & Development
3 stages
1. Embryogenesis
Fertilization to seed
2. Vegetative growth
Juvenile stage
Germination to adult
"phase change" marks transition
3. Reproductive development
Make flowers, can
reproduce sexually
Light regulation of growth
Plants sense
1. Light quantity
2. Light quality (colors)
3. Light duration
4. Direction it comes from
Light regulation of growth
Measures night! 30" flashes during night stop flowers
LDP plants such as Arabidopsis need long days to flower
SDP flower in fall, LDP flower in spring, neutral flower
when ready
Next : color matters! Red light works best for flowering
Phytochrome
Next : color matters! Red light (666 nm)works best for
flowering & for germination of many seeds!
But, Darwin showed blue works best for phototropism!
Phytochrome
But, Darwin showed blue works best for phototropism!
Different photoreceptor!
Red light (666 nm) promotes germination
Far red light (>700 nm) blocks germination
Phytochrome
Red light (666 nm) promotes germination
Far red light (>700 nm) blocks germination
After alternate R/FR color of final flash decides outcome
Seeds don't want to germinate in the shade!
Pigment is
photoreversible
Phytochrome
Red light (666 nm) promotes germination
Far red light (730 nm) blocks germination
After alternate R/FR color of final flash decides outcome
Pigment is photoreversible! -> helped purify it!
Looked for pigment that absorbs first at 666 nm, then 730
Phytochrome
Red light (666 nm) promotes germination
Far red light (730 nm) blocks germination
After alternate R/FR color of final flash decides outcome
Pigment is photoreversible! -> helped purify it!
Looked for pigment that absorbs first at 666 nm, then 730
Phytochrome
Red light (666 nm) promotes germination
Far red light (730 nm) blocks germination
After alternate R/FR color of final flash decides outcome
Pigment is photoreversible! -> helped purify it!
Looked for pigment that absorbs first at 666 nm, then 730
Made as inactive cytoplasmic Pr that absorbs at 666 nm
Phytochrome
Made as inactive cytoplasmic Pr that absorbs at 666 nm or
in blue
Converts to active Pfr that absorbs far red (730nm)
Phytochrome
Made as inactive cytoplasmic Pr that absorbs at 666 nm or
in blue
Converts to active Pfr that absorbs far red (730nm)
97% of Pfr is converted back to Pr by far red light
Phytochrome
Made as inactive cytoplasmic Pr that absorbs at 666 nm or
in blue
Converts to active Pfr that absorbs far red (730nm)
97% of Pfr is converted back to Pr by far red light
Also slowly reverts in dark
Phytochrome
Made as inactive cytoplasmic Pr that absorbs at 666 nm or
in blue
Converts to active Pfr that absorbs far red (730nm)
97% of Pfr is converted back to Pr by far red light
Also slowly reverts in dark: how plants sense night length
Types of Phytochrome Responses
Two categories based on speed
1. Rapid biochemical events
2. Morphological changes
Types of Phytochrome Responses
Two categories based on speed
1. Rapid biochemical events
2. Morphological changes
Lag time also varies from minutes to weeks
Types of Phytochrome Responses
Two categories based on speed
1. Rapid biochemical events
2. Morphological changes
Lag time also varies from minutes to weeks: numbers of
steps after Pfr vary
Types of Phytochrome Responses
Lag time also varies from minutes to weeks: numbers of
steps after Pfr vary
"Escape time" until a response can no longer be reversed
by FR also varies
Types of Phytochrome Responses
Lag time also varies from minutes to weeks: numbers of
steps after Pfr vary
"Escape time" until a response can no longer be reversed
by FR also varies: time taken for Pfr to do its job
Conclusions: phytochrome acts on many processes in
many ways
Types of Phytochrome Responses
Two categories based on speed
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
Types of Phytochrome Responses
Two categories based on speed
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
• Changes 0.02% of Pr to Pfr
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
• Changes 0.02% of Pr to Pfr
• Are not FR-reversible!
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
• Changes 0.02% of Pr to Pfr
• Are not FR-reversible! But action spectrum same as Pr
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
• Changes 0.02% of Pr to Pfr
• Are not FR-reversible! But action spectrum same as Pr
• Induced by FR!
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
• Changes 0.02% of Pr to Pfr
• Are not FR-reversible! But action spectrum same as Pr
• Induced by FR!
Obey law of reciprocity:
1 nmol/m-2 x 100 s =
100 nmol/m-2 x 1 sec
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
• Changes 0.02% of Pr to Pfr
• Are not FR-reversible! But action spectrum same as Pr
• Induced by FR!
Obey law of reciprocity:
1 nmol/m-2 x 100 s =
100 nmol/m-2 x 1 sec
Examples: Cab gene
induction, oat
coleoptile growth
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
• Changes 0.02% of Pr to Pfr
• Are not FR-reversible! But action spectrum same as Pr
• Induced by FR!
Obey law of reciprocity:
1 nmol/m-2 x 100 s =
100 nmol/m-2 x 1 sec
Examples: Cab gene
induction, oat
coleoptile growth
2. LF: induced by
1 µmol/m-2, saturate @
1000 µmol/m-2
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
Are FR-reversible!
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
Are FR-reversible! Need > 3% Pfr
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
Are FR-reversible! Need > 3% Pfr
Obey law of reciprocity
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
Are FR-reversible! Need > 3% Pfr
Obey law of reciprocity
Examples : Lettuce seed
Germination, mustard
photomorphogenesis,
inhibits flowering in SDP
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
Are FR-reversible! Need > 3% Pfr
Obey law of reciprocity
Examples : Lettuce seed
Germination, mustard
photomorphogenesis,
inhibits flowering in SDP
3. HIR: require prolonged
exposure to higher fluence
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
3. HIR: require prolonged exposure to higher fluence
Effect is proportional to
Fluence
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
3. HIR: require prolonged exposure to higher fluence
Effect is proportional to
Fluence
Disobey law of reciprocity
Are not FR-reversible!
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
3. HIR: require prolonged exposure to higher fluence
Effect is proportional to fluence
Disobey law of reciprocity
Are not FR-reversible!
Some are induced by FR!
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
3. HIR: require prolonged exposure to higher fluence
Effect is proportional to fluence
Disobey law of reciprocity
Are not FR-reversible!
Some are induced by FR!
Examples: inhibition of
hypocotyl elongation in
many seedlings,
Anthocyanin synthesis
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
3. HIR: require prolonged exposure to higher fluence
Effect is proportional to fluence
Disobey law of reciprocity
Are not FR-reversible!
Some are induced by FR!
Examples: inhibition of
hypocotyl elongation in
many seedlings,
Anthocyanin synthesis
Different responses =
Different phytochromes
Types of Phytochrome Responses
3 classes based on fluence (amount of light needed)
1. VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2
2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2
3. HIR: require prolonged exposure to higher fluence
Different responses = Different phytochromes:
3 in rice, 5 in Arabidopsis
Types of Phytochrome Responses
Different responses = Different phytochromes:
3 in rice, 5 in Arabidopsis
1. PHYA mediates VLF and HIR due to FR
Types of Phytochrome Responses
Different responses = Different phytochromes:
3 in rice, 5 in Arabidopsis
1. PHYA mediates VLF and HIR due to FR
• Very labile in light
Types of Phytochrome Responses
Different responses = Different phytochromes:
3 in rice, 5 in Arabidopsis
1. PHYA mediates VLF and HIR due to FR
• Very labile in light
2. PHYB mediates LF and HIR due to R
• Stable in light
Types of Phytochrome Responses
1. PHYA mediates VLF and HIR due to FR
• Very labile in light
2. PHYB mediates LF and HIR due to R
• Stable in light
3. Roles of PHYs C, D & E not so clear
Types of Phytochrome Responses
1. PHYA mediates VLF and HIR due to FR
• Very labile in light
2. PHYB mediates LF and HIR due to R
• Stable in light
3. Roles of PHYs C, D & E not so clear
PHYA & PHYB are often antagonistic.
Types of Phytochrome Responses
PHYA & PHYB are often antagonistic.
In sunlight PHYB mainly controls development
Types of Phytochrome Responses
PHYA & PHYB are often antagonistic.
In sunlight PHYB mainly controls development
In shade PHYA 1st controls development, since FR is high
Types of Phytochrome Responses
PHYA & PHYB are often antagonistic.
In sunlight PHYB mainly controls development
In shade PHYA 1st controls development, since FR is high
But PHYA is light-labile; PHYB takes over & stem grows
"shade-avoidance"
Phytochrome
Pr has cis-chromophore
Phytochrome
Pr has cis-chromophore
Red converts it to trans = active shape
Phytochrome
Pr has cis-chromophore
Red converts it to trans = active shape
Far-red reverts it to cis
Phytochrome
Pfr is a protein kinase: acts by kinasing key proteins
• some stays in cytoplasm & activates ion pumps
Phytochrome
Pfr is a protein kinase: acts by kinasing key proteins
• some stays in cytoplasm & activates ion pumps
• Rapid responses are due to changes in ion fluxes
Phytochrome
Pfr is a protein kinase: acts by kinasing key proteins
• some stays in cytoplasm & activates ion pumps
• Rapid responses are due to changes in ion fluxes
• Increase growth by activating PM H+ pump
Phytochrome
Pfr is a protein kinase: acts by kinasing key proteins
• some stay in cytoplasm & activate ion pumps
• Rapid responses are due to changes in ion fluxes
• most enter nucleus and kinase transcription factors
Phytochrome
some stay in cytoplasm & activate ion pumps
• Rapid responses are due to changes in ion fluxes
most enter nucleus and kinase transcription factors
• Slow responses are due to changes in gene expression
Phytochrome
most enter nucleus and kinase transcription factors
• Slow responses are due to changes in gene expression
• Many targets of PHY are transcription factors, eg PIF3
Phytochrome
most enter nucleus and kinase transcription factors
• Slow responses are due to changes in gene expression
• Many targets of PHY are transcription factors, eg PIF3
• Activate cascades of genes for photomorphogenesis
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Phytochrome
Slow responses are due to changes in gene expression
Many targets of PHY are transcription factors, eg PIF3
Activate cascades of genes for light responses
Some overlap, and some are unique to each phy
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Phytochrome
Slow responses are due to changes in gene expression
Many targets of PHY are transcription factors, eg PIF3
Activate cascades of genes for light responses
Some overlap, and some are unique to each phy
20% of genes are light-regulated
Phytochrome
• 20% of genes are light-regulated
• Protein degradation is important for light regulation
Phytochrome
• 20% of genes are light-regulated
• Protein degradation is important for light regulation
• Cop mutants can’t degrade specific proteins
Phytochrome
• Protein degradation is important for light regulation
• Cop mutants can’t degrade specific proteins
• COP1/SPA targets specific transcription factors for
degradation
Phytochrome
• Protein degradation is important for light regulation
• Cop mutants can’t degrade specific proteins
• COP1/SPA targets specific
TF for degradation
• DDA1/DET1/COP10 target
other proteins for degradation
Phytochrome
• Protein degradation is important for light regulation
• Cop mutants can’t degrade specific proteins
• COP1/SPA targets specific
TF for degradation
• DDA1/DET1/COP10 target
other proteins for degradation
• Other COPs form part of
COP9 signalosome
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•
Phytochrome
Protein degradation is important for light regulation
Cop mutants can’t degrade specific proteins
COP1/SPA targets specific TF for degradation
DDA1/DET1/COP10 target other proteins
Other COPs form part of COP9 signalosome
W/O COPs these TF act in dark
Phytochrome
• COPs target specific TF for degradation
• W/O COPs they act in dark
• In light COP1 is exported to cytoplasm so TF can act
• Tags PHYA by itself on the way out!
Other Phytochrome Responses
In shade avoidance FR stimulates IAA synthesis from trp!
Occurs in < 1 hour
Other Phytochrome Responses
In shade avoidance FR stimulates IAA synthesis from trp!
Occurs in < 1 hour
Also occurs in response to endogenous ethylene!
Other Phytochrome Responses
Flowering under short days is controlled via protein deg
• COP & CUL4 mutants flower early
Other Phytochrome Responses
Flowering under short days is controlled via protein deg
• COP & CUL4 mutants flower early
• Accumulate FT (Flowering locus T) mRNA early
• FT mRNA abundance shows strong circadian rhythm
Other Phytochrome Responses
Circadian rhythms
• Many plant responses, some developmental, some
physiological, show circadian rhythms
Circadian rhythms
Many plant responses, some developmental, some
physiological, show circadian rhythms
Leaves move due to circadian ion fluxes in/out of dorsal &
ventral motor cells
Circadian rhythms
Many plant responses show circadian rhythms
• Once entrained, continue in constant dark
Circadian rhythms
Many plant responses show circadian rhythms
• Once entrained, continue in constant dark, or light
Circadian rhythms
Many plant responses show circadian rhythms
• Once entrained, continue in constant dark, or light!
• Gives plant headstart on photosynthesis, other
processes that need gene expression
Circadian rhythms
Many plant responses show circadian rhythms
• Once entrained, continue in constant dark, or light!
• Gives plant headstart on photosynthesis, other
processes that need gene expression
• eg elongation at night!
Circadian rhythms
Gives plant headstart on photosynthesis, other processes
that need gene expression
• eg elongate at night!
• Endogenous oscillator is temperature-compensated, so
runs at same speed at all times
Circadian rhythms
Endogenous oscillator is temperature-compensated, so
runs at same speed at all times
• Is a negative feedback loop of transcription-translation
• Light & TOC1 activate LHY & CCA1 at dawn
Circadian rhythms
Light & TOC1 activate LHY & CCA1 at dawn
LHY & CCA1 repress TOC1 in day, so they decline too
Circadian rhythms
Light & TOC1 activate LHY & CCA1 at dawn
LHY & CCA1 repress TOC1 in day, so they decline too
At night TOC1 is activated (not enough LHY & CCA1)
Circadian rhythms
Light & TOC1 activate LHY & CCA1 at dawn
LHY & CCA1 repress TOC1 in day, so they decline too
At night TOC1 is activated (not enough LHY & CCA1)
Phytochrome entrains the clock
Circadian rhythms
Light & TOC1 activate LHY & CCA1 at dawn
LHY & CCA1 repress TOC1 in day, so they decline too
At night TOC1 is activated (not enough LHY & CCA1)
Phytochrome entrains the clock So does blue light