Photoinduced division synchrony in permanently bleached Euglena gracilis

Ultraviolet light-induced, bleached Euglena clones exhibit synchronous steps of cell division in response to daily cycles of light and dark. The cyclic division activity, in the bleached cells, will persist in constant lighting conditions with a period, independent of temperature, of about 24 h. This persisting rhythm of cell division supports the hypothesis that this phase of the cell cycle may be coupled to the fluctuations of the endogenous circadian clock of the cell.Newly isolated bleached clones are sensitive to light in their growth rates and metabolic characteristics, showing light induced difference in substrate-stimulated respiration, and production of the polyglucan, paramylon. After repeated subculturing of a bleached clone the photosensitivity of the metabolic characteristics and of the growth rate are diminished along with the ability to photo-entrain division synchrony. Division control and the induction of cell synchrony in this organism apparently involve both the temporal influence of the endogenous cell clock and one or more other photosensitive reactions in the metabolism of the cell.A unique culture mixing technique utilizing the bleached Euglena, failed to support the hypothesis of the involvement of intercellular communication in the maintenance of cell synchrony in constant lighting conditions.