Reduction of survival and induction of chromosome aberrations in tobacco irradiated by carbon ions with different linear energy transfers

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PURPOSE: To determine the relationship between linear energy transfer (LET) and the relative biological effectiveness (RBE) for survival reduction and chromosome aberration induction in plants. MATERIALS AND METHODS: Tobacco seeds were exposed to carbon ions having LET ranging from 92 to 260 keV microm(-1). Survival ratc was determined at 7 weeks after sowing. Chromosome aberrations were observed when the root length reached about 0.5 mm (immediately after radicle emergence), 3 and 10 mm. RESULTS: The RBE for both endpoints increased with increasing LET and showed the highest value at 230 keV um(-1). The highest RBE was 65.0 for survival reduction and 52.5 for chromosome aberration induction. The types and yield ratio of chromosome aberrations such as fragments and bridges were not affected by radiation type at 0.5mm root length. As the roots elongated from 0.5 to 10 mm, the frequency of aberrant cells gradually decreased. The number of cells with fragments decreased faster than the number of cells with bridges. The decrement of chromosome aberrations appeared to be slower in roots irradiated by carbon ions than in roots irradiated by gamma-rays. CONCLUSIONS: The results show a close relationship between survival reduction and chromosome aberration induction in plants. The types and yield ratio of initial chromosome aberrations did not differ among gamma-rays and carbon ions with different LET.