Quantitative analysis of DNA double-strand breaks in tobacco cells irradiated by heavy ions

Abstract

The ability of ion beams to kill or mutate plant cells is known to depend on LET of the ions, although the mechanism of damage is poorly understood. In this study, DNA double-strand breaks (DSBs) were quantified by a DNA fragment-size analysis in tobacco protoplasts irradiated with high-LET heavy ions. Tobacco BY-2 protoplasts, as a model of single plant cells, were irradiated by helium, carbon and neon ions with different LETs at ice temperature. Resulting DNA fragments were separated into sizes by pulsed-field gel electrophoresis. Initial DSB yields and intervals between neighboring DSBs were evaluated from the DNA fragmentation patterns. Initial DSB yields (Gbp DNA^-1 Gy^-1) were found to depend on LET, and the highest value was obtained at 124 and 241 keV/μm carbon ions in the investigated range. High-LET carbon and neon ions induced DSBs at closer sites than gamma rays did. These results partially explained the large biological effects caused by high-LET heavy ions in plants.