A far-red form of phytochrome exhibiting in vivo spectral properties: Studies with crude extracts of oats and squash

Abstract

Crude extracts from etiolated oat and squash seedlings can be obtained which exhibit spectroscopic properties for the far-red form of phytochrome similar to those exhibited by phytochrome in vivo. These extracts are prepared from tissue which has been irradiated in vivo with red light. Extracts of non-irradiated tissue which receive a red treatment in vitro show a far-red phytochrome peak at shorter wavelength than the in vivo location. An extract made from tissue that has been given red followed by far-red light shows the same far-red peak location after red irradiation in vitro as an extract prepared from non-irradiated tissue. Far-red treatment of an extract of red-irradiated tissue converts phytochrome to the red-absorbing form; reconversion to the far-red form by red light gives a far-red peak shifted to shorter wavelength. It is suggested that the in vitro long-wavelength far-red phytochrome species, which exhibits in vivo spectral properties, could possibly correspond to a form of phytochrome still associated with its native active site.