Biological effects of ion beams in Nicotiana tabacum L.

The biological effects of ion beams on Nicotiana tabacum L., particularly t he induction of chromosome aberrations, were investigated. Dry seeds were e xposed to C-12(5+), He-4(2+) and H-1(+) beams with linear energy transfer ( LET) ranging from 1 to 111 keV/mu m and irradiated with gamma-rays. Ion bea ms were more effective in reducing germination and survival of the seeds th an gamma-rays. The LD50 for C-12(5+) beams, He-4(2+) beams and gamma-rays w ere 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 ex; posed seeds, increased linearly with increasing doses. Relative biological effectiveness (RBE) va lues, 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 C-12(5+) beams, 7.0-8 .3 for the He-4(2+) beams and 7.8 for the H-1(+) beams. Furthermore, the re lative ratios of the chromosome aberration types were significantly differe nt be tween the ion beam and the gamma-ray regimes: chromosome fragments we re more frequent in the former, and chromosome bridges in the latter. Based on these rer suits, we concluded that the repair process of initial lesion s induced by ion beams may be different from that induced by low- LET radia tion.