The Repair of Sub-lethal Damage and the Stimulated Repair of Potentially Lethal Damage in Saintpaulia

Summary

The repair of sublethal and potentially lethal damage in stationary resting epidermal cells of Saintpaulia has been investigated. Fractionation experiments revealed an efficient repair of sublethal damage with a half-life of 1·9 hours. No repair of potentially lethal damage was noted when cultivation of the leaves was delayed for 24 hours after irradiation. At delay times of 2, 3 and 4 days some repair of potentially lethal damage has been found. A small pre-dose given 24 hours before a challenging dose improved the cells' chance to regenerate and the improvement has been shown to be compatible with an improved repair of potentially lethal damage induced by X-rays and fast neutrons. It has been shown that the stimulated repair process takes 12 to 24 hours to develop, is dependent on the size of the pre-dose, has single-hit dose kinetics, and an r.b.e. of 1 for neutrons. With delayed cultivation of 2 days the stimulated repair process leads to an alteration in the shape of the regeneration (survival)—dose relationship which increases the low dose r.b.e. for neutrons from 10 to 35.