AN ACTION SPECTRUM OF PHYTOCHROME BINDING TO A SUBCELLULAR FRACTION OF MAIZE COLEOPTILES

Abstract— An action spectrum was constructed for the photo-induced pelletability of phytochrome in excised coleoptiles of etiolated maize seedlings. It closely resembled the absorption spectrum of purified phytochrome in the P, form as reported in the literature. The spectral dependence of phytochrome pelletability effected by sustained irradiation (4 h) was also determined and it appeared remarkably similar to the high irradiance response (HIR) action spectrum reported for the inhibition of lettuce hypocotyl lengthening. The induction action spectrum was held to support the conclusion that phytochrome itself is the photoreceptor for its own binding to the subcellular fraction of maize coleoptiles and that the binding phenomenon is an early, if not the first, physiological consequence of irradiation. Also a modified version of Hartmann's interpretation of the high irradiance response was given.