Negative necrotaxis.

We studied necrotaxis in several strains of protists and compared the reaction of living cells in the vicinity of cells killed by a ruby laser. Negative necrotaxis was observed for the unicellular green alga Euglena gracilis, whereas Chlamydomonas was shown to exhibit positive necrotaxis. The cellular colony Pandorina morum exhibited no reaction to the killing of nearby colonies. Both the colorless cryptomonad Chilomonas paramecium and the ciliate Tetrahymena pyriformis exhibited negative necrotaxis following the lysis of vitally stained specimens of their own species. They also exhibited negative necrotaxis following the lysis of Euglena cells. It was also demonstrated that the cellular content of Euglena cells lysed by heat or by a mechanical procedure acts as a repellent to intact Euglena cells. These results suggest that the negative necrotaxis provoked in Euglena by the laser irradiation is probably due to the chemotactic effect produced by the release of cell content in the extracellular medium. This cell content could, according to its chemical composition, act either as a repellent, an attractant, or be inactive. The sensitivity of cells (specific or nonspecific ion channels or chemoreceptors) are also of prime importance in the process.

[The effect of gamma irradiation on the strain W of Tetrahymena pyriformis]. / Vplyv gama-ziarenia na Tetrahymena pyriformis kmen W.

It the present study the effects of gamma-radiation at doses of 102.1 Gy-1,633.4 Gy were investigated as exerted on the protozoan Tetrahymena pyriformis W strain. An investigation of lethality showed that all irradiated cells survived after the doses of 102.1 Gy and 204.2 Gy, When the doses of 408.4 and 816.7 Gy were applied, 60.6% and 8.8%, resp., of irradiated cells survived. Not a cell survived the dose of 1,633.4 Gy. The effects of gamma-radiation on the generation time of Tetrahymena pyriformis are shown in Tab. II. A markedly longer generation time than in the control was observed if the radiation doses made 408.4 and 816.7 Gy. There were no significant changes there when the effects of irradiated incubation media on the growth of nonirradiated cells of the W strain of Tetrahymena pyriformis were investigated. The results confirmed the relatively high radioresistance of the Tetrahymena protozoon with respect to gamma-radiation; this protozoan is a suitable biological model for a study of the effects of various kinds of ionizing radiation at the level of both cell and population.

The effect of varying illumination on imprinting of Tetrahymena by insulin.

Tetrahymena pyriformis cultures were imprinted with insulin. Hormone binding was reduced in the dark, but alternation of dark and light periods were in this respect more effective than the dark itself. The deviations observed may be attributed, besides the reduced insulin binding by the imprinted cells in the dark, to an enhanced binding by the non-imprinted control cells kept in the dark. It is suggested that the dark-induced structural transformation of the membrane, manifesting among others in a changed hormone binding, may be caused by alterations in haem synthesis due to varying illumination.

Ionizing radiation promotes protozoan reproduction.

This experiment was performed to determine whether ionizing radiation is essential for maximum growth rate in a ciliated protozoan. When extraneous ionizing radiation was reduced to 0.15 mrad/day, the reproduction rate of Tetrahymena pyriformis was significantly less (P less than 0.01) than it was at near ambient levels, 0.5 or 1.8 mrad/day. Significantly higher growth rates (P less than 0.01) were obtained when chronic radiation was increased. The data suggest that ionizing radiation is essential for optimum reproduction rate in this organism.

[The effect of ultraviolet irradiation on the protozoan Tetrahymena pyriformis]. / Vplyv ultrafialového ziarenia na prvoka Tetrahymena pyriformis.

A number of trials was conducted to test the effect of ultraviolet radiation on the protozoan Tetrahymena pyriformis, strain W. The material was cultivated in a culture medium and in a deficient experimental medium, the radiation flux being 90 to 5400 J/m2 in the logarithmic and stationary stages of population growth. As found, the culture medium has a protective effect against ultraviolet radiation, owing to an increased peptone content. The cells in the stationary stage of growth are more resistant to ultraviolet radiation than cells in the logarithmic stage of growth. The studied intensities of radiation did not damage the nutrients contained in the medium.

[Effect of ultraviolet irradiation on infrastructure and mitotic activity of Tetrahymena pyriformis]. / Action de l'irradiation ultraviolette sur l'infrastructure et l'activité prolifératrice de Tetrahymena pyriformis.

Effects of U.V. irradiation, 3,600 erg/mm2, administrated at a low dose rate, over 75 mn at the very beginning of the cell cycle, were investigated in Tetrahymena pyriformis. Irradiation results in mitotic activity changes, followed either by cell death or cell survival with subsequent normal division activity. Nucleolar fusion, possible intracytoplasmic extrusion of nucleolar aggregates and particular pictures of nucleologenesis are described. Simultaneous cytoplasmic lesions can contribute to the delayed death of Tetrahymena after U.V. irradiation.

Radiation-induced fluctuation of the polysome content in adequately oxygenated tetrahymena pyriformis.

The polysome content of the ciliate protozoan Tetrahymena pyriformis is transiently reduced by gamma-irradiation. In order to test whether this is a result of a respiration-produced or radiation-produced hypoxia or some other mechanism, the oxygen content of the culture was determined during and after irradiation, and the polysome contents and rates of amino acid incorporation were measured with and without air bubbling. Irradiation (40 krad at approximately 3 krad/min) produced approximately a 25 per cent loss in dissolved O2 content in the medium. This decrease is not sufficient to affect the polysome level, since (a) the same radiation-induced loss of polysomes and inhibiition of amino acid incorporation was observed whether or not the culture was bubbled with air during the irradiation and (b) bubbling unirradiated cultures with gas mixtures containing as little as 17 per cent of the normal O2 content did not influence the polysome level. As long as the cells are irradiated as a shallow layer in open flasks, replacement of O2 from the gas phase appears adequate, and neither respiration-induced nor radiation-induced hypoxia masks the effects of the radiation.

Selective inhibition of precursor incorporation into ribosomal RNA in gamma-irradiated Tetrahymena pyriformis.

Sublethal doses of gamma radiation are known to inhibit total RNA synthesis in the ciliate protozoan Tetrahymena. To determine if the synthesis of a particular class of RNA is preferentially inhibited, pulse-labeled RNA was isolated from normal exponentially growing cells, irradiated cells, and cells in which total RNA synthesis had recovered to the pre-irradiation level. The RNAs were analyzed by SDS-polyacrylamide gel electrophoresis and oligo(dT)-cellulose column chromatography. Inhibition of RNA synthesis primarily involves ribosomal RNA. However, radiation does not cause a delay in the processing of precursor rRNA or a preferential loss of either of the mature rRNAs. Following irradiation, poly(A)-containing RNA [poly(A+)RNA] is synthesized at a rate up to three times greater than the control rate. The elevated poly(A+)RNA synthesis occurs during the period of depressed rRNA synthesis and even after rRNA synthesis has recovered to its pre-irradiation rate. While the sizes of the total cellular ribonucleoside triphosphate pools are depressed in the irradiated cells, these pools probably do not represent the actual compartments containing the precursors for RNA synthesis, and the observed changes cannot explain the modifications in macromolecular synthesis in irradiated Tetrahymena.

[On the increase of phototoxic activities of polycyclic aromatic hydrocarbons produced by dish detergents (author's transl)]. / Uber die Steigerung phototoxischer Wirkungen polyzyklischer Aromaten durch Haushaltsspülmittel (Tenside).

Several bands of dish detergents were found in high dilutions to increase phototoxic cell damage produced by polycyclic hydrocarbons such as benzo(a)pyrene. A comparable increase in phototoxicity in the presence of detergents was observed following the phagocytic ingestion of photodynamically active soot particles by the test organisms, Tetrahymena pyriformis (ciliate). The results are considered in the light of earlier reports on increased carcinogenicity following detergent action of one of the brands used in this investigation (P) on benzo(a)-pyrene. Possible mechanisms of action of detergents producing the increase in respective activities are discussed.

[On the interaction of polycyclic aromatic hydrocarbons and light with regard to its syncarcinogenic effects (author's transl)]. / Uber das Zusammenwirken von polyzyklischen Aromaten und Licht unter dem Gesichtspunkt der Synkanzerogenese

The rapidly growing pollution of the human biosphaere with potentially carcinogenic agents gives increased relevance to questions concerning the interaction of both chemical and physical agents in carcinogenesis. One such combination of environmental agents - that between polycyclic aromatic hydrocarbons and light - which heretofore has received little attention from workers in the field of environmental research, was investigated in the present paper. The phototoxic (cytotoxic) effects of carcinogenic aromatic hydrocarbons was demonstrated using ciliates of the species Tetrahymena pyriformis as the sensitive substrate. The experiments were conducted both with the chemically pure compounds and with native soot containing the adsorbed hydrocarbons. The following results were obtained: 1. Phototoxicity for ciliates of the highly carcinogenic benzo(a)pyrene may still be demonstrated in dilutions containing but 2 ppb (mug/l) of the substance, while the non-carcinogenic benzo(e)pyrene and fluorenthene are only weakly toxic in much higher concentrations. 2. The combination of benzo(a)pyrene and fluoranthene produced neither an additive nor a quenching effect, i.e., the resulting phototoxicity merely reflected the action of benzo(a)pyrene. 3. No phototoxic effect was observed in case of the fluorescent carcinogen, aflatoxin B1, in concentrations up to 200 ppb. This is taken to indicate that the property of fluorescence of carcinogenic substances by itself does not account for the phototoxic phenomenon. 4. The intense phototoxic activity of native soot ingested by the ciliates was shown to be dependent on the amount of polycyclic hydrocarbons contained. 5. Removal of polycyclic aromatic hydrocarbons from the soot particles by extraction with benzene resulted in the loss of phototoxic activity.