Action Spectra for Photoaccumulation of Green and Colorless Euglena: Evidence for Identification of Receptor Pigments

Abstract—Phototaxis action spectra have been determined in three different types of Euglena gracilis; green and dark‐bleached cells containing the stigma and streptomycin‐treated white mutant with an absorptionless stigma. In all three types of microorganisms the flavin containing paraflagellar body is present. The shape of the action spectrum is the same for the three types of cells and proportional to the absorption spectrum of flavoproteins. It has been shown that the structure of the action spectrum does not depend on the presence of screening organelles, on which, instead, depends the direction of the response to the light stimulus. It is concluded that the flavin chromophores present in the photoreceptor are the pigments responsible for phototaxis in Euglena gracilis.