The degree of photoreactivation or rever"~al of injurious effects of ultraviolet radiations (UV) by illumination with visible light has been shown to increase with length of exposure of the irradiated organisms to visible light (Dulbecco, 1949; Kelner, 1951). After maximal photoreactivation of phage has been achieved, further illumination with whitelight has no further effect (Dulbecco, 1949), whereas in EsckericMa coli and Streptomyces griseus additional illumination proved to be injurious in some cases (Keiner, 1951). Photoreactivation in Colpidium coIpod~ increases with exposure to monochromatic or mixed visible light to a maximal value. Additional illumination to the extent previously tried was not injurious (Giese, Brandt, Iverson, and Wells, 1952). The question arises as to how many quanta of visible light are necessary to reverse maximally the action of 1 quantum of UV. This information would be interesting for theoretical reasons. The present report records such determinations for Colpidium colpoda, a ciliate protozoan. Metkods and MaterialsAs a criterion of UV injury the retardation of the third division of the irradiated colpidia was determined in much the same way as in previous experiments with paramecia (Giese, 1939). Photoreversal was measured by recovery from such division delay.Fortunately Colpidiura colpoda like Paramecium caudatura (Giese, 1939(Giese, , 1945 does not show a period of cessation of division after UV treatment as does P. aurdia or P. mul~iraicronucleatura (Giese and Reed, 1940;Kimball and Gaither, 1951) or Tarahymena geleii (Christensen, unpublished). Therefore the delay in the third division after irradiation may be determined without this complication. The methods were in general similar to those described in the previous paper . (Giese, Brandt, Iverson, and Wells, 1952).As a source of radiation a quartz mercury arc was used and the radiations were passed through a natural quartz monochromator. The 2654 A line in the short UV was reflected by a fight angle quartz prism upon the horizontally held quartz cell containing the protozoa. For photoreactivation the light from a high pressure Ames
Starvation increases the susceptibility of Paramecium and Colpidium to ultraviolet (UV) radiations (Giese and Reed, 1940;Giese et al., 1954). Injury to starved colpidia is found to be less readily photoreversed than that to well fed animals, eight times as many quanta of blue light per quantum UV being required for maximal photoreversal (Giese et a/., 1953). Refeeding them with bacteria after UV but before blue light has little effect upon the degree of photoreversal (Giese eta/., 1954). Since it is difficult to tell how much food a bacterial feeder like Colpidium has ingested and how soon the food has been metabolized, the effect of feeding on UV injury and its photoreversal was studied with Didinium nasutura, a carnivorous ciliate. This species was chosen because its food intake can be easily observed under the microscope and regulated. It normally eats paramecia which can be grown under fairly controlled conditions. Therefore if the number of paramecia supplied to a didlnium is controlled, the quantity and quality of food intake is known. The effect of the nutritional state upon susceptibility to UV and on photoreversal of UV injury by visible light is reported below. Material and MethodsThe dirllnla were irradiated with monochromatic short UV (2654 A) the intensity of which, measured by a thermopile calibrated against U. S. Bureau of Standards' standard lamps, varied from 8.67 to 4.64 ergs/sec./mm, ffi during the course of the experiments. They were photoreversed with monochromatic blue light (4350 A), the intensity of which varied from 565 to 294 ergs/sec./mm. ~ One fraction of a population of irradiated didinia was illuminated within a few minutes after UV treatment; another was kept as a dark control (UV). The methods have been described in some detail in previous work with Colpidium (Giese el a/., 1952). All observations were made in red light which does not photoreactivate.Didinia were fed upon paramecia grown in test tubes on a single strain of bacteria in the manner previously described (Giese and Taylor, 1935). Freshly excysted didinia were much more constant in division rate and susceptibility to UV than *Supported in part by contract AT(11-1)-234 with the Atomic Energy Commission.
Many previous workers have found low intensity ultraviolet (UV) radiation less effective than high intensity UV in producing injury to various living organisms (Christensen, 1953;Coblentz and Fulton, 1924;Dreyer, 1903;Gates, 1929; Swann and del Rosario, 1932;Weinstein, 1930;Wyckoff, 1932). Experiments performed here on the protozoan Didinium nasutum, indicated an opposite, greater effect of low intensity UV. It appeared likely that a dark reaction succeeds the absorption of UV, so that quanta are supplied at high intensity more rapidly than they can be utilized; i.e., saturation occurs. To investigate this possibility the UV was flashed and the dark period between flashes varied, with the expectation of increased injury with longer dark periods. Since a dark reaction is thermochemical, it should proceed more rapidly at high than at low temperature, and injury should therefore increase with temperature. Experiments were accordingly carried out at various temperatures. The expectations have been confirmed in the present study. The effects of variable light period and flash rate, and the comparison of flashed high intensity with continuous low intensity irradiation have also been explored. Materials and MethodsCultures of Didinium nasutum were grown in 4 ram. bore isolation tubes on concentrated suspensions of Paramecium caudatum in the manner previously described (Brandt el a/., 1955). Didinia selected at random for a sample were irradiated in a quartz cell, put into isolation tubes with food, one animal per tube, and the number ha each tube was recorded three times daily, as a rule, until the fourth division was reached ha all tubes. This stage was usually reached earlier in some tubes than ha others, and the tubes were discarded as they attained it, since higher counts were difficult to make, and were likely to be biased because of rapid depletion of the food supply.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.