PHYTOCHROME

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PHYTOCHROME
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Photo- morphogenesis
Skoto- morphogenesis
Etiolated
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How can we interpret these effects of light?
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LIGHT AS A HORMONE
What does a hormone need to act?
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LIGHT AS A HORMONE
What does a hormone need to act?
A receptor In this case a photo
receptor
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How can this happen??
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Phytochrome A light photoreceptor
Protein 125 kDa Chromophore
Red light (650 - 680 nm) Far red light (710 -
740 nm)
The ligand
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Phytochrome A light photoreceptor
Protein 125 kDa Chromophore
Red light (650 - 680 nm) Far red light (710 -
740 nm)
The ligand
TWO LIGANDS!!
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Photoreversibility
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Photoreversibility
RED hn
Pr
Pfr
FAR RED hn
What does this remind you of???
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Photoreversibility
kinase
X
X-P
phosphatase
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Pr
Pfr
Pr
Pr
Pfr
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Pr
Pfr
Pr
Lag time Escape time
Pr
Pfr
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Pr
Pfr
HYPOTHETICAL ABSORPTION SPECTA
Absorbance
660
740
Wavelength
RED hn
Pr
Pfr
FAR RED hn
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Real spectra!
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Photostationary state
740 nm
How much Pr? Pfr?
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Photostationary state
740 nm Pr Pfr 97 Pr Pfr 3
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Photostationary state
660 nm
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Photostationary state
660 nm Pr Pfr 80 Pr Pfr 20
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The Score So Far
Light is a hormone
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Phytochrome is a photoreceptor
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Photoswitchable between Red and Far red
absorbing forms
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Complex absoprtion spectra
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The Bunsen Roscoe Reciprocity Law
Fluence rate x time Response magnitude
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The Bunsen Roscoe Reciprocity Law
Fluence rate x time Response magnitude
µmol m-2 s-1 x s µmol m-2
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1st internode length, mm
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Pfr
1st internode length, mm
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1/10 firefly flash
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What happens after a ligand binds to a recepor?
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Membrane
Cell
Pr
Cytoplasm
Nucleus
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Where might phytochrome be?
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Pr
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Nucleus
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Phytochrome
Holoprotein Apoprotein Chromophore
Phytochromobilin
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Two-Component regulation
Phospho-transfer
Origin of plant phytochrome
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The Score So Far
Three different response families
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Phytochrome structure is light regulated
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Phytocrhome is a kinase ... ustabe
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