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LET dependence of lethality of carbon ion irradiation to single tobacco cells

Purpose: To determine the radiation sensitivity and relationship between linear energy transfer (LET) and relative biological effectiveness (RBE) in single plant cells irradiated with heavy ions. Materials and methods: Single cells were isolated from the tobacco BY‐2 cell line and irradiated with carbon ions (78.6–309 keV µm−1) and gamma‐rays (0.2 keV µm−1). Two weeks after irradiation, colonies with 16 cells or more derived from the irradiated cells were counted as survivors. The surviving fraction was fitted using the single‐hit, multitarget theory. Results: The doses needed to reduce the surviving fraction of the cells to 0.1 (D10) of gamma‐rays and carbon ions were 47.2 and 10.5–12.6 Gy, respectively. The RBE based on the D10 peaked at an LET of 247 keV µm−1. The inactivation cross‐section of carbon ions reached a plateau of 11.3 µm2 at an LET of 247 keV µm−1. Conclusions: The radiation sensitivity of single tobacco cells was much lower than that of mammalian cells, although the mean number of base pairs per chromosome in the two cell types was similar. The RBE peak based on the D10 of carbon ions in single tobacco cells occurred at a higher LET than it does in other organisms.