Radiosensitivity and the Oxygen Effect Measured at Different Phases of the Mitotic Cycle Using Synchronously Dividing Cells of the Root Meristem of Vicia faba

Vicia seedlings were immersed in a solution of hydroxyurea for a period of 24 hours. The meristematic cells were partially synchronized by this treatment; 11 hours after removal from the hydroxyurea, 40% of the cells were in mitosis. Seedlings were exposed to x-rays at various times after removal from hydroxyurea-that is, with the meristematic cells at different phases of their mitotic cycle. Radiosensitivity was assessed in terms of growth inhibition of the primary root and was found to vary widely through the cell cycle, reaching a maximum when most meristematic cells were in mitosis. Irradiations were carried out under aerated and hypoxic conditions; it was found that the oxygen enhancement ratio did not change significantly with phase of the mitotic cycle.