Absorption Spectra of Phytochrome Intermediates

Native phytochrome (124 kdalton) was isolated from etiolated seedlings of Avena sativa L. cv. Pirol (Baywa, Munich). From low temperature spectra (0°C to - 165 °C) of phytochrome samples irradiated either with red or far-red light, spectra of intermediates were calculated. Both absorption bands of the phytochrome chromophore were reported. On the pathway Pr → Pfr, native phytochrome does not form a bleached intermediate (meta-Rb) in contrast to degraded phytochrome. An additional intermediate, meta-Rc (λmax = 725 nm), is formed instead. On the reverse pathway only two intermediates were found, lumi-F and meta-F. Oscillator strengths′ values were calculated and interpreted in terms of chromophore conformation. A scheme of intermediates for native phytochrome is presented.