The Effect of Tritium Oxide on Some Synthetic Processes of Chlorella Pyrenoidosa

Abstract

Previous papers (1, 2), which reported on the effect of several concentrations of tritium oxide on growth, division, average cell diameter, and viability of Chlorella, showed that there is a time-lag in the appearance of growth or cell division inhibition when cells are grown in the presence of tritium oxide. Then the inhibition increases, in terms of percent of surviving cells that cease to grow and divide, with each unit of time. Further, the effect continues in subculture in nonradioactive nutrient solution, and the length of time and magnitude of inhibition are a function of the dose of radiation the cells receive. The major effect of the irradiation is, of course, death of the cell. The fact that there is a time-lag in the appearance of growth inhibition or other effects of ionizing radiations suggested that if one could determine the quantity of various cellular compounds or fractions synthesized by irradiated and control cells it might be possible to show that irradiation affects one biosynthetic system more than another, or that the main effect of ionizing radiations is a general slowing of all reactions. Should one reaction system be affected more than others, then possibly one or more enzymes involved in that system would be damaged, or the ability to synthesize one or more enzymes of the system would be impaired or lost. Should all systems be damaged to the same extent then, possibly, damage would be to a process controlling the rate of increase of Chlorella. Such a process might be one or more of the reactions involved in cell respiration or division. Damage might also occur through random hits of ionizing particles within molecules of the cell. If so, a certain number of hits, the number dependent upon the molecules hit, would cause death of the cells; there would be no uniform change in the metabolism of the cells that were hit previous to the death of the cell. We therefore grew tritium-irradiated and unirradiated Chlorella for 24-30 hours in the presence of C14 bicarbonate and then fractionated the cells. C14 was used to increase the sensitivity of analysis since the quantity of cells available was below