1. Julia Rausenberger Zentrum für Biosystemanalyse Universität Freiburg
An integrative and quantitative model for phyB mediated photomorphogenesis: From protein dynamics to physiology
Julia Rausenberger
Zentrum für Biosystemanalyse
Universität Freiburg
GRK Begutachtung
18. Februar 2010

2. Aspects of photomorphogenesis
Adapted from Quail (2002)
red light
Skotomorphogenesis vs. Photomorphogenesis
Alternative developmental programs during early plant growth: light-dependent de-etiolation
Phytochrome B:
Dimeric protein about 125kDa
Abundant in red light (660nm)
Two reversibly photointerconverting forms
Nuclear complexes
early, transient
late, stable
Mediated reactions:
Growth of hypocotyl length
Magnitude of cotyledon areas
Taken from Bae & Choi (2008)

3. What makes the phytochrome system interesting for theoreticians?Pr
 = 0.85
k1, 660 nm
k2, 660 nm
Pfr R Pr
Pfr
 = 0.03
k1, 730 nm
k2, 730 nm FR
at equilibrium:
d[Pfr]/dt = 0 = k1[Pr] - k2[Pfr]
[Pfr]/[Ptot] =  = k1 / (k1 + k2) Pr
Pfr
k1
k2
Adjustable parameters:
spectral composition of incident light
light intensity (photon flux)
duration of irradiation
protein dynamics can be changed by switching on/off the light

4. Time resolved hypocotyl growth
Darkness
Continuous red light
phyB-9
Col WT
phyB-OX
Hypocotyl growth is a standard read-out for phytochrome signaling.
When grown in darkness, the three phenotypes show the same S-shaped growth profile.
Light-grown seedlings also exhibit an S-shaped growth curve, but the final hypocotyl length vary due to the presence of active phytochrome.
No active phytochrome present
How does active phytochrome
influence hypocotyl growth?

5. Investigations of growth patterns
Hypocotyl dark growth is characterized by:
Asymmetric S-shaped growth curve L
Asymmetric bell-shape of velocity function dL/dt
-> growth rate is not constant over time
J. Sachs (1874): ”large period of growth”: growth velocity increase -> maximum -> growth velocity decrease
G. Backman (1931): Integration of the growth velocity yields S- shaped growth curve: “growth cycle”
 γ determines the asymmetry of L and dL/dt
Biological time
Growth
rate
Environmental limitation

6. How does active phytochrome come into play?
End-point-analysis (after 4 days)
darkness
continuous red light
Biological time
Modified growth
rate
Environmental limitation
Scale bar = 10μm