(C) Absorption spectra of PR and PFR 0.8 O.4 Figure 18.23 Structure and func- tion of phytochromes. (A) The phytochrome 300 40O SOO 600 70O 8O0 chromophore is a tetra- pyrrole that binds to the Wavelength (nm) phytochrome protein (B) The C termini of plant phytochromes may contain two distinct (D) Phytochrome activities transmitter kinase do- mains, TKD2 and TKDI 660nm lopmental (C) Absorption spectra R f Pr and PFR show 730nm responses peaks for red (66o nm) and far-red (730 nm) light, respectively. (D)Phytochromes can 660nm exist as either of two interconvertible forms 730nm germination Isolated phytochromes in a concentrated solu- tion can undergo re- 660nm versible changes in absorbance induced by 730nm illumination with red or far-red light. These light-induced structural Greening of changes are coincident with physiological and seedling developmental changes Figure 9-5-3 induced by red light or blocked by far-red light.Figure 9-5-3