Effects of ion beam irradiation on mutation induction and nuclear DNA content in chrysanthemum

We investigated the effects of ion beams, in comparison to gamma rays, on mutation induction and nuclear DNA content as an index of radiation damage in Chrysanthemum morifolium. Leaf segments were irradiated with 220 MeV carbon ions (mean linear energy transfer = 107 keV/mu m), 320 MeV carbon ions (76 keV/mu m), 100 MeV helium ions (9 keV/mu m), and gamma rays. The nuclear DNA content was measured and frequency of flower color mutations was investigated in regenerated plants. The number of plants with reduced nuclear DNA content increased with increasing irradiation doses of 320 MeV carbon ions, 100 MeV helium ions, and gamma rays. In contrast, they did not increase with 220 MeV carbon ions, even when the dose was increased. Irradiation treatment with 220 and 320 MeV carbon ions and gamma rays had a similar effect on mutation induction, while the effect of 100 MeV helium ions was not as great. Thus, the effects of irradiation treatments on mutation induction and nuclear DNA content differed according to the type of ion beams. 220 MeV carbon ion beam seemed to be the most appropriate among the three types of ion beams because it gave a high mutation frequency with low damage to chromosomes.