Absorption Spectra of Phytochrome Intermediates

Native phytochrome (124kdalton) was isolated from etiolated seedlings o f Avena sativa L. cv. Pirol (Baywa, Munich). From low temperature spectra (0 °C to — 165°C ) o f phytochrom e samples irradiated either with red or far-red light, spectra o f intermediates were calculated. Both absorption bands o f the phytochrome chromophore were reported. On the pathway P r i V r , native phytochrome does not form a bleached intermediate (m eta-Rb) in contrast to degraded phytochrome. An additional intermediate, meta-Rc ( / max = 725 nm), is formed instead. On the reverse path­ way only two intermediates were found, lum i-F and meta-F. Oscillator strengths’ values were calculated and interpreted in terms o f chromophore conformation. A schem e o f interm ediates for native phytochrome is presented.