Phytochromes and Etiolation
Bio 1400
Biological Inquiry
e’-tee-oh-la-shun
Signal Transduction
• conversion of stimulus to cellular response
– integrated orchestrated events
• extracellular signal
• causes cellular response
– signal is transduced from outside of cell to inside
to set up response
Receptors receive stimulus from
outside the cell
CELL
WALL
CYTOPLASM
stimulus chemical and
electrical signals
Cell response: change
in gene expression
DNA  RNA protein
Phytochrome structure in plants
How do phytochromes work in plants?
Phytochrome synthesis
biologically
ACTIVE form
of phytochrome
red light converts Pr to Pfr
Pr
continual
production of Pr
in plant:
biologically
INACTIVE form
Pfr
far-red light converts Pfr to Pr
sunlight contains both red
and far-red, thus an
equilibrium is reached: 60%
Pfr to 40% Pr
Phytochrome synthesis
biologically
ACTIVE form
of phytochrome
red light converts Pr to Pfr
Pr
continual
production of Pr
in plant:
biologically
INACTIVE form
Pfr
far-red light converts Pfr to Pr
Dark Reversion in
long dark periods
Electromagnetic Radiation from Sun
far-red 700-800nm
Absorption spectra of phytochrome forms
660nm
730nm
Two parts of phytochrome:
chromorphore and protein
Phytochrome chromophore (Pr form)
http://plantphys.info/plant_physiology/phytoch
rome.shtml
SIGNAL TRANSDUCTION:
https://www.youtube.com/watch?v=3I2bSMm06IA&noredirect=1
Process that allows conversion of light energy
chemical and electrical energy  gene expression
Changes in wavelength of light are
detected by phytochromes
http://www.bio.miami.edu/dana/226/226F08_21.html
Watch the animation for more details
• http://highered.mheducation.com/sites/9834
092339/student_view0/chapter41/animation_
-_phytochrome_signaling.html
On your own:
• Perform an internet search to investigate the
function of vertebrate photoreceptors.
• How are these proteins similar to
photoreceptors in plants? How are they
different?
• Bring your findings for discussion in class on
Thursday, 2-12-15