Effects of space balloon flights on reproductive activity in Paramecium aurelia

Post autogamous Paramecium aurelia cultures were placed in hermetic containers, including a heating device with accuracy kept around +/- 0.1 degrees C. Kinetics of cellular growth was determined by cell count, after recovery, on in-flight cultures and ground control cultures. Dosimetry was performed by thermoluminescent detectors (CaSO4 activated with dysprosium). Flight durations of maximum altitude (ceiling) ranged between 48 min and 15 hours (repeated flights). Conclusions are as follows: short flights result in a secondary stimulating effect, shown by post-flight increase of the growth rate (total dose above 2 mrads); long flights or repeated flights are accompanied by a decrease in growth rate (total dose ranging from 2 to 6 mrads); in the stimulation experiments, cell counts performed immediately after flight permit identification of a temporary decrease of growth rate. The biphasic character of the biological response after flights may be due to an ionization phenomena induced by cosmic rays. Indeed, the temporary drop of growth rate is not observed after recovery if the cells are subcultured in fresh medium and left on the earth's surface. We observe, on the contrary, an increase in growth rate. These findings confirm the great sensitivity of Paramecium aurelia to very low doses of ionizing radiations and demonstrate the biological effect of cosmic radiation.