The fine structure of the alga Brachiomonas submarina bohlin after X- and γ-irradiation

Abstract

The green alga, Brachiomonas submarina, was subjected to varying exposures of X- and γ-radiation and the fine structure examined at various postirradiation times. Exposures were in the range of those inhibiting colony formation rather than causing cell lysis. Discernible effects of irradiation were most prominent in cells fixed 5 hr after an exposure of X-rays sufficient to inhibit colony formation 50 per cent and in cells examined at daily intervals following an exposure of γ-rays sufficient to inhibit colony formation completely. The cytological effects observed included rupture of the nuclei and nuclear envelopes, presence of cells with lobed nuclei or two nuclear bodies, enlarged vacuoles, swollen and distorted mitochondria with changes in the cristae, an increased number of mitochondria, increased amounts of starch, and possible changes in the chloroplast and dictyosomes. None of these effects was observed in control cells. Nuclear and cytoplasmic damage was observed concurrently at certain postirradiation times but not necessarily in the same cells. Fine structural damage was similar to that which is known to occur in other cell types following exposure to ionizing radiation. The cytoplasmic damage could be sufficient to result in cell death, but until it can be quantified and its physiological significance interpreted and extended to various species, the nucleus should continue to be considered the most probable primary site of radiation damage.