On the interrelations between ultraviolet and visible light during their simultaneous action on the cell

Beyond the Earth's atmosphere, ultraviolet (UV) light that is a component of the Sun's spectrum appears as one of the limiting factors to life in space and on the planets which have no ozone layer in their atmosphere. At early stages in the evolution of life, the Earth's atmosphere contained neither free oxygen nor the layers serving as a screen for short-wave UV light. Under such conditions, the UV radiation lasted for 8-10 hours a day. Similar radiation conditions may be found on Mars. Still, we do not know to what extent the photo-reactivating region of sun radiation (3000-5490 angstroms) can protect cells from the action of short UV light. Therefore, it will be of interest to study a prolonged action of UV radiation on living systems (protozoa, bacteria, fungi, animal and plant cells) in the presence of visible rays capable of reactivating UV damage. We subjected infusoria (Paramecium caudatum) to prolonged action of UV light (2537 angstroms). The cells were irradiated daily for 8-16 hours with doses of 1.5-40 and 120 mkvt. A sharp reduction in the rate of division and the lethality to the infusoria were observed from the second to the fifth day of experimentation. In the light variant, UV radiation was performed simultaneously with the application of visible light (2800-15000 lux). In such conditions, the cells kept their normal rate of division for 12 days. In the next 30 days without irradiation, no deviation from the normal rate was noted. The experimental results permit the conclusion that under certain conditions of interaction between visible and UV light, UV does not produce a deleterious effect on cell division.