THE USE OF A COMPUTERIZED SPECTRORADIOMETER TO PREDICT PHYTOCHROME PHOTOEQUILIBRIA UNDER POLYCHROMATIC IRRADIATION

Abstract A method is described for predicting the effect of polychromatic irradiation upon the photo-stationary equilibrium of the plant photoreceptor phytochrome. This method follows from the rate equations for phototransformation and utilizes the in vivo action spectra for phytochrome phototransformation (Pratt and Briggs, 1966). A scanning spectroradiometer interfaced with a microcomputer is used to determine a spectral photon distribution from 360 to 800 nm. The products of the photon fluence rate and the relative quantum efficiencies at 2-nm intervals are summed over the entire visible range to yield a predicted percentage of the pigment in the Pfr form. This value was determined under eight different polychromatic light sources and was generally within 7% Pfr of the value measured in etiolated corn coleoptiles under the same light sources.