The spectral properties of Pfrin extracts prepared from red-irradiated oat tissue are similar to those for Pfras measured in vivo, with a spectral peak at about 732 nm. The presence or absence of Mg2+or EDTA in the extraction medium is without effect on the spectral properties of the Pfrextracted from red-irradiated tissue. In contrast, the spectral properties of Pfrformed in vitro in extracts of non-irradiated oat tissue cleared of particulate matter are markedly different, the absorption peak being at about 725 nm. However, the red irradiation of the crude extract prior to its being cleared of particulate matter, results in the formation of a Pfr-species with spectral properties similar to Pfras seen in vivo, suggesting the requirement for some particulate fraction for the formation of the long-wavelength Pfrform. The long-wavelength “activated” form of Pfronce extracted and partially purified is highly stable both at 0° and 25°C. Photoconversion of this long-wavelength form of Pfrto Prinitially results in the formation of a Prspecies with a peak at 662 nm. In contrast, the peak location of Pras isolated from non-irradiated tissue is at 6
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