Mutagenic effects of carbon ions near the range end in plants

Hase, Yoshihiro; Yoshihara, Ryohei; Nozawa, Shigeki; Narumi, Issei

To gain insight into the mutagenic effects of accelerated heavy ions in plants, the mutagenic effects of carbon ions near the range end (mean LET: 425 keV/m) were compared with the effects of carbon ions penetrating the seeds (mean LET: 113 keV/m). Mutational analysis by plasmid rescue of from irradiated Arabidopsis plants showed a 2.7-fold increase in mutant frequency for 113 keV/m carbon ions, whereas no enhancement of mutant frequency was observed for carbon ions near the range end. This suggested that carbon ions near the range end induced mutations that were not recovered by plasmid rescue. An Arabidopsis DNA ligase IV mutant, deficient in non-homologous end-joining repair, showed hyper-sensitivity to both types of carbon-ion irradiation. The difference in radiation sensitivity between the wild type and the repair-deficient mutant was greatly diminished for carbon ions near the range end, suggesting that these ions induce irreparable DNA damage. Mutational analysis of the Arabidopsis locus showed that while the frequency of generation of glabrous mutant sectors was not different between the two types of carbon-ion irradiation, large deletions (30 kb) were six times more frequently induced by carbon ions near the range end. This suggests that the proportion of large deletions increases with LET in plants.