Presentation on theme: "Julia Rausenberger Zentrum für Biosystemanalyse Universität Freiburg"— Presentation transcript:
1Julia Rausenberger Zentrum für Biosystemanalyse Universität Freiburg An integrative and quantitative model for phyB mediated photomorphogenesis: From protein dynamics to physiologyJulia RausenbergerZentrum für BiosystemanalyseUniversität FreiburgGRK Begutachtung18. Februar 2010
2Aspects of photomorphogenesis Adapted from Quail (2002)red lightSkotomorphogenesis vs. PhotomorphogenesisAlternative developmental programs during early plant growth: light-dependent de-etiolationPhytochrome B:Dimeric protein about 125kDaAbundant in red light (660nm)Two reversibly photointerconverting formsNuclear complexesearly, transientlate, stableMediated reactions:Growth of hypocotyl lengthMagnitude of cotyledon areasTaken from Bae & Choi (2008)
3What makes the phytochrome system interesting for theoreticians? Pr = 0.85k1, 660 nmk2, 660 nmPfrRPrPfr = 0.03k1, 730 nmk2, 730 nmFRat equilibrium:d[Pfr]/dt = 0 = k1[Pr] - k2[Pfr][Pfr]/[Ptot] = = k1 / (k1 + k2)PrPfrk1k2Adjustable parameters:spectral composition of incident lightlight intensity (photon flux)duration of irradiationprotein dynamics can be changed by switching on/off the light
4Time resolved hypocotyl growth DarknessContinuous red lightphyB-9Col WTphyB-OXHypocotyl 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 presentHow does active phytochromeinfluence hypocotyl growth?
5Investigations of growth patterns Hypocotyl dark growth is characterized by:Asymmetric S-shaped growth curve LAsymmetric bell-shape of velocity function dL/dt-> growth rate is not constant over timeJ. Sachs (1874): ”large period of growth”: growth velocity increase -> maximum -> growth velocity decreaseG. Backman (1931): Integration of the growth velocity yields S- shaped growth curve: “growth cycle” γ determines the asymmetry of L and dL/dtBiological timeGrowthrateEnvironmental limitation
6How does active phytochrome come into play? End-point-analysis (after 4 days)darknesscontinuous red lightBiological timeModified growthrateEnvironmental limitationScale bar = 10μm