Low temperature spectroscopy of phytochrome: Pr, Pfr and intermediates

Phytochrome (120 kdalton) was isolated from etiolated seedlings of Avena sativa L. cv. Pirol (Baywa, München). Low temperature spectra between −17°C and −160°C are recorded for P_r, P_fr, and irradiated phytochrome samples. The temperature-dependence of the P_r and P_fr absorption spectra is described. Difference spectra of such temperature effects can erroneously be interpreted as difference spectra of intermediates. Probable absorption spectra of intermediates are calculated from the spectra of irradiated P_r or P_fr, respectively. The calculated spectral data are compared with published data on phytochrome intermediates.