[A fluorescence phenomenon of nucleoprotein shown by illuminated living cells]

Living cell nuclei supravitally stained with fluorochromes exhibit a rapid fluorescence fading during continuous light or u.v. illumination. Subsequently the fluorescence intensity is transitory restored due to increased influx of new dye molecules and their interaction with nucleoproteins. This effect is interpreted as photodynamic (photosensitized) action concerning nuclear macromolecules. It can be shown with different intercalating and nonintercalating fluorochromes. Continued illumination causes cell damage and cell death. Fractionated illumination allows to investigate fluorescence recovery and other restitutional processes on the level of living eucaryotic cells.