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

Yokota, Yuichiro; Hase, Yoshihiro; Shikazono, Naoya; Tanaka, Atsushi; Inoue, Masayoshi*

To determine the radiation sensitivity and the relationship between linear energy transfer (LET) and relative biological effectiveness (RBE) in single plant cells irradiated with heavy ions, single tobacco (BY-2) cells were irradiated with carbon ions (78.6 to 309 kev/m) and gamma rays (0.2 kev/m). Two weeks after the irradiation, colonies derived from the irradiated cells that had 16 cells or more were counted as survivors. The surviving fraction was fitted using the single-hit, multitarget theory. The dose needed to reduce the surviving fraction of the cells to 0.1 (D) of gamma rays and carbon ions were 47.2 and 10.5 to 12.6 Gy, respectively. 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 is similar. The RBE based on the D peaked at a LET of 247 keV/m. The RBE peak based on the D of carbon ions in single tobacco cells occurred at a higher LET than it dose in other organisms.