Abstract
High linear-energy-transfer (LET) radiations such as alpha particle brought by radon are included in environmental radiation. Therefore, to consider about effects of environmental radiation on ecological systems and their members, LET dependencies of their radiation effects should be elucidated. However, there are a few findings of radiation effects and its LET dependencies in plants, although plants are a majority of ecological systems and occupy an important position of them. We have been thus estimated cell killing effects based on colony formation and been quantified initial yields of DNA double-strand breaks (DSBs) by pulsed-field gel electrophoresis assay in protoplasts that were isolated from dicot tobacco cultured cell line (BY-2) and irradiated with high-LET (8.9-440 keV/μm) heavy ions. As a result, both effects of cell killing and DSB induction depended on LET, and indicated peak effectiveness per dose by irradiation of carbon ions having LETs of 247 keV/μm and 124-241 keV/μm respectively. These dependencies are similar to those of survival reduction reported in dicot dormat seeds. In contrast, it is reported that carbon ions having LETs of 100-150 keV/μm maximize the cell killing effects per dose in mammalian cells. They are also reported that the killing effects of heavy ions peak at around 100 keV/μm in yeasts and Bacillus subtilis, and that there is no peak of the effects in Deinococcus radiodurans. From these facts, it was cleared that LET dependencies of radiation effects are not always common among various organisms and the LET values giving the maximal lethal effects are higher in plants than in the other organisms. We must take care to compare the LET dependencies of DSB induction among organisms because different types of methods for quantifying DSBs can lead different results. In this workshop, we will also discuss about the relationships between strategies of genome maintenance and LET dependencies of radiation-induced biological effects in plants.
