Studies on the capacity of Pr in vitro to photoconvert to the long-wavelength Ffr-form. A survey of ten plant species

Studies on the capacity of Pr in uitro to photoconvert to the long wavelength in uioo-like Pfr form were performed with extracts from 10 species. Red irradiation, immediately after extraction of crude extracts from 9 species, photoconverted Pr to long-wavelength Pfr with an absorbance maximum around 735 nm. Red irradiation of soybean extracts, however, photoconverted Pr to short-wavelength Pfr, with an absorbance maximum at 725 nm. Red irradiation given later than 1.5-2 h after extraction, to extracts of oats, pea, cucumber, radish, sunflower and soybean, photoconverted Pr to a short-wavelength Pfr species with an absorbance maximum around 725 nm. In crude extracts of barley, corn, wheat and zucchini, red irradiation, even after a long dark-incubation period at 4°C of up to 48 h, photoconverted Pr to long-wavelength Pfr with an absorbance maximum around 735 nm. After incubation at 25°C for 3 h, however, Pr from barley also photoconverted to the short-wavelength form. It is suggested that in the group exemplified by oats, Pr rapidly undergoes an alteration following extraction, which results in the loss of the capacity of Pr to photoconvert to long-wavelength Pfr. In contrast, in extracts from the group exemplified by barley, Pr is much more stable and retains the capacity to photoconvert to long-wavelength Pfr for much longer periods.