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

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 mmu, the other between 600 and 700 mmu. peaking at about 660 mmu. 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 disappearance. 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, we conclude that phytochrome acts as a photoreceptor for the photoactivation of its metabolically-based destruction. We suggest that another pigment might also be associated with the disappearance of phytochrome in oat seedlings exposed to blue light.