Abstract
Potted plants of Tradescantia ohiensis (=T. reflexa) were chronically exposed to 60Co gamma-rays at exposure rates of 2.3 to 18.5R/day (115 to 925mR/hr) in the gamma field of the National Institute of Radiation Breeding. Other potted plants were placed on the protection earth bank surrounding the gamma field (Fig. 1) and were exposed to a low level (280mR/day or 14mR/hr) of scattering radiation. The genetic effects of these radiation treatments were studied in the stamen hairs (essentially single-meristematic-cell system) at two different periods.
Evident genetic responses to these radiation treatments were clearly observed. Somatic mutation rates increased roughly linearly with increasing daily exposure of gamma rays. The gamma-ray exposure given during hair development induced somatic pink mutations at a rate of 3.36×10-4 pink mutant events per hair per R effective exposure. It was estimated that the gamma-ray exposure given during hair development was almost twice as efficient as those given before hair development. The frequency of pink mutant cells in the hair cell population also increased roughly linearly with increasing daily exposure. The frequency per cell per R effective exposure reached the value of 8.78×10-5.
Genetic effects more than expected were observed in the stamen hairs irradiated with scattering radiation at a very low exposure rate of 280mR/day at the top of the earth bank of the gamma field. Namely, the mutation rates by this treatment were almost as high as those by 2.3R/day gamma-ray irradiation in the gamma field. It is suspected that the scattering radiation may have seven to eight times more efficiency than the direct 60Co gamma rays.
The stamen hair system of Tradescantia heterozygous for flower color was proved to be a sensitive biometrical system for detecting low levels of radiation exposures (e.g., ca. 2R exposure during hair development plus ca. 2.5R exposure before hair development at 280mR/day exposure rate). The present results obtained by using Tradescantia stamen hairs seem to throw doubt on the safety standards for radiation facilities.
