The Phototransformation Pathway of Dimeric Oat Phytochrome From the Red‐light‐absorbing Form to the Far‐red‐light‐absorbing Form at Physiological Temperature Is Composed of Four Intermediates

Abstract— –Phototransformation of oat type I phytochrome in vitro from the red‐light‐absorbing form (Pr) to the far‐red‐light‐absorbing form (Pfr) at physiological temperature (24°C) was investigated with a multichannel transient spectrum analyser. Four sequential intermediates were detected between Pr and Pfr. Absorption spectra of these intermediates suggested that three of them corresponded with the intermediates lumi‐R, meta‐Ra and meta‐Rc detected earlier at low temperature spectroscopy. A new intermediate named meta‐Rb was found in the pathway between meta‐Ra and meta‐Rc. The new intermediate is not identical with meta‐Rb previously detected at low temperature. The rate constant of Pfr appearance in isolated oat phytochrome dissolved in buffer containing 5% (vol/vol) glycerol was similar to that of etiolated pea epicotyl tissue.