Figure 4.
Calculated dynamic response of PhyB and PIF3 after light induction. In (a) the response for the first 3 hours and in (b) the response during the first 24 hours. In darkness (t < 0) there are no phytochromes in the Pfr form and the level of PIF3 is high. After light induction at t = 0 the phytochromes switch (approximately instantaneously) to the Pfr form. The faster decay of Pfr compared to Pr gives that the Pfr (and thus total PhyB) level decrease with time after the light-switch as is seen in both (a) and (b). The PIF3 concentration is initially decreasing rapidly since Pfr induce phosphorylation of PIF3 followed by degradation by 26S-proteasomes. Morover, since Pfr is also decreasing, the phosphorylation rate of PIF3 decrease and PIF3 will after the initial rapid decay slowly increase somewhat after the first day. As a reference for the calculated model data and for parameter estimates, we have in (a) inserted PhyB and PIF3 data (circles) from figure 7F in ref.32 and in (b) PhyB data (squares) extracted from Fig. 4C in ref.26.