Effects of sparsely and densely ionizing radiation on monocellular green alga Chlorella vulgaris

Though relative biological effectiveness (RBE) of different types of ionizing radiation is intensely studied, mechanisms responsible for difference in the relative biological effectiveness are still not clear. Comparative analysis of effects of sparsely and densely ionizing radiation on monocellular green alga Chlorella vulgaris is presented in the paper. It is shown that survival curves of cells exposed to both types of radiation have exponential shape. In contrast to Chlorella cells, survival curves of other studied biological objects exposed to sparsely ionizing radiation have sigmoid shape. The death of both the alga cells and other objects from exposure to a-particles is significantly higher than after delivery the same dose of sparsely ionizing radiation. Chlorella vulgaris cells have several modes of radiation induced cell death, such as interphase death, apoptosis and necrosis, observed before cells division or after several cell division cycles. If doses of exposure of cells in log to both types of radiation are isoeffective, the number of interphase cell death caused by exposure of log-phase cells to alpha-particles is twofold higher than after gamma-radiation, the ratio is 1.5 for stationary-phase cells. Results of the study will improve understanding of mechanisms of eukaryotic cells inactivation induced by ionizing radiation with different LET.