Analysis of mutations induced by carbon ions in

To investigate the nature of mutations induced by accelerated ions in higher plants, the effects of carbon-ion-irradiation were compared with those of electron-irradiation in Arabidopsis thaliana. Point-like mutations and rearrangements were induced at a similar fre-quency after carbon-ion-irradiation, whereas point-like mutations were more frequently induced after electron-irradiation. Sequence analysis revealed that carbon-ion-induced point-like mutations were mostly short deletions. In the case of rearrangements, deletions, in-versions, insertions, and translocationswere found. The estimated frequency of deletion induction was compar-able to that of fast neutrons. Analysis of chromosome breakpoints revealed that carbon ions frequentlydeleted small regionsaround thebreakpoints,whereaselectron-irradiation often duplicated these regions. Moreover, for both types of radiation, broken ends with micro-homologies were frequently rejoined. Results of the breakpoint and broken end analyses suggest that non-homologous end-joining (NHEJ) leads to the rejoining of double strand breaks (dsbs) after cells are exposed to both types of radiation, but the type of NHEJ that occurs as a result of damage is different. The results indicated that carbon-ion-induced mutations are most likely nulls and that the induced rearrangements may arise through a unique mechanism. These findings indicate that ac-celerated ions are a usefulmutagen for both forward and reverse genetics for plants