ELIMINATION OF PHOTORECEPTOR (PARAFLAGELLAR SWELLING) AND PHOTORECEPTION IN EUGLENA-GRACILIS BY MEANS OF THE CAROTENOID BIOSYNTHESIS INHIBITOR NICOTINE

Nicotine is the chief representative of tobacco alkaloids. It is a commonly used insecticide, and has been reported to be a potent and reversible inhibitor of carotenoid biosynthesis. It inhibits cyclohexylidene ring formation in the biosynthetic sequence leading to beta-carotene. This specificity prompted us to investigate the influence of this alkaloid on the photoreceptor of Euglena gracilis in an attempt to confirm our previous microscopic data which indicated that the chromophores present in the photoreceptor could be related to carotenoids. The effects of nicotine at various concentrations on the photoreceptor of Euglena gracilis and its photoreception were investigated using phase-contrast microscopy, fluorescence microscopy, transmission electron microscopy and photobehaviour. Nicotine affects the formation of the photoreceptor, after five cell generations. Photoaccumulation experiments on nicotine-treated Euglena cells clearly show that these cells are unable to see light. These results strongly confirm the presence of a chromophore related to carotenoids in the photoreceptor of Euglena gracilis. On removal of nicotine, cells again acquire their physiological status.