Mutagenic effects of carbon ions near the range end in plants.

To gain insight into the mutagenic effects of accelerated heavy ions in plants, the mutagenic effects of carbon ions near the range end (mean linear energy transfer (LET): 425 keV/mu m) were compared with the effects of carbon ions penetrating the seeds (mean LET: 113 keV/mu m). Mutational analysis by plasmid rescue of Escherichia coli rpsL from irradiated Arabidopsis plants showed a 2.7-fold increase in mutant frequency for 113 keV/mu 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 GL1 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 (>similar to 30 kb) were six times more frequently induced by carbon ions near the range end. When 352 keV/mu m neon ions were used, these showed a 6.4 times increase in the frequency of induced large deletions compared with the 113 keV/mu m carbon ions. We suggest that the proportion of large deletions increases with LET in plants, as has been reported for mammalian cells. The nature of mutations induced in plants by carbon ions near the range end is discussed in relation to mutation detection by plasmid rescue and transmissibility to progeny. (C) 2011 Elsevier B.V. All rights reserved.