Abstract
To analyze mutagenic effects of ionizing radiation in higher plant, seeds of transgenic Arabidopsis carrying rpsL gene were irradiated with carbon ions (LET=112keV/μm) and gamma-rays. The doses were adjusted to give the same effect on survival reduction. Both carbon-ion and gamma-ray irradiation resulted in a 2.6 times increase of mutant frequency. The mutant frequency per unit dose was higher in carbon ions than in gamma-rays. Mutation spectrum showed that the carbon ions and gamma-rays frequently induced G:C to A:T transition and deletions. In addition, the carbon ions induced complex-type mutations and the gamma-rays induced frameshift mutations with relatively higher frequency. The G:C to T:A and A:T to C:G transversions, which are caused by oxidized guanine, were hardly found in our experiment, although those are major mutations induced by gamma-rays in many other organisms. The difference in cellular environment between seeds and proliferating cells may affect radiation-induced mutation spectrum.
Carbon ions with shallower penetration depth that give a maximum LET in the seeds had higher lethal effect pet unit dose than the carbon ions that penetrates the seeds. However, mutant frequency was remained at control level. High-LET radiations are known to induce chromosomal rearrangement such as large deletion, inversion and translocation. Since the rpsL mutation analysis system only detects intragenic mutations, our result suggests that the carbon ions near the Bragg peak less frequently induce small intragenic mutations in the Arabidopsis dry seeds.
