The biological effects of ion beams on Nicotiana tabacum L., particularly the induction of chromosome aberrations, were investigated. Dry seeds were exposed to 12C5+, 4He2+ and 1H+ beams with linear energy transfer (LET) ranging from 1 to 111 keV/microm and irradiated with gamma-rays. Ion beams were more effective in reducing germination and survival of the seeds than gamma-rays. The LD50 for 12C5+ beams, 4He2+ beams and gamma-rays were 35, 60 and 500 Gy, respectively. The frequencies of mitotic cells with chromosome aberrations, such as chromosome bridges, acentric fragments and lagging chromosomes in the root tip cells of the exposed seeds, increased linearly with increasing doses. Relative biological effectiveness (RBE) values, based on the doses that induced a survival inhibition of 50% and a 10% frequency of aberrant cells, were 14.3-17.5 for the 12C5+ beams, 7.0-8.3 for the 4He2+ beams and 7.8 for the 1H+ beams. Furthermore, the relative ratios of the chromosome aberration types were significantly different between the ion beam and the gamma-ray regimes: chromosome fragments were more frequent in the former, and chromosome bridges in the latter. Based on these results, we concluded that the repair process of initial le
The induction of chromosome aberrations in tobacco root tip cells was measured after exposure to either 18 MeV/n carbon ions or 2 MeV electrons. The RBE value for acute exposure was found to be about 10. Splitting the dose into two fractions did not produce any significant effect on the yield of aberrations following carbon-ion exposure, whereas a clear decrease was observed after exposure to electrons thereby indicating an induction/activation of error-free repair after the first fraction. Moreover, this decrease appeared to be independent of the types of chromosome aberrations. On the other hand, it was suggested that the lack of any significant effect on the yield of aberrations is either due to a lack of error-free repair or to a less efficient damage repair after exposure to carbon ions.
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