Action Spectrum and Characteristics of the Light Activated Disappearance of Phytochrome in Oat Seedlings

Abstract

The action spectrum for the light-activated destruction of phytochrome in etiolated Avena seedlings has been determined. There are 2 broad maxima, one between 380 and 440 m u, the other between 600 and 700 m u, peaking at about 660 m u. On an incident energy basis, the red region of the spectrum is more efficient than the blue by about one order of magnitude in activating phytochrome diasppearance. Both the red-absorbing as well as the far-red-absorbing forms of phytochrome are destroyed after exposure of Avena seedling to either red or blue light. From the action spectrum and photoreversibility of pigment loss, it is inferred that phytochrome acts as a photoreceptor for the photo-activation of its metabolically-based destruction. It is suggested that another pigment might also be associated with the disappearance of phytochrome in oat seedlings exposed to blue light.