An early genetic study showed that most radiation-induced mutations are not transmitted to progeny. In recent molecular studies in plants, mainly M2 plants or their progeny, which contain only transmissible mutations, have been analyzed, but the early results imply that these studies are insufficient as comprehensive descriptions of radiation-induced mutations. To study radiation-induced mutations caused by low-LET gamma-rays and high-LET carbon ions at the molecular level, we used the pollen-irradiation method and the plant Arabidopsis thaliana to study various mutations, including nontransmissible mutations. This analysis revealed that most mutants induced with irradiation with gamma-rays (150-600 Gy) or carbon ions (40-150 Gy) carried extremely large deletions of up to >6 Mbp, the majority of which were not transmitted to progeny. Mutations containing 1- or 4-bp deletions, which were transmitted normally, were also found. Comparison of the deleted regions in the mutants showing various manners of transmission suggests that the nontransmissibility of the large deletions may be due to the deletion of a particular region that contains a gene or genes required for gamete development or viability.