Morphologically abnormal cells, somatic mutations and loss of reproductive integrity in irradiated Tradescantia stamen hairs

Abstract

Inflorescences of Tradescantia clone 02, a diploid clone heterozygous for flower color (stamen hair color), were exposed to 69, 180 and 282 R of 137Cs gamma rays at an exposure rate of 23·5 R/min. Stamen hairs were observed for 20 days after irradiation in order to record the numbers of stunted hairs (composed of fewer cells than normal), morphologically abnormal cells and somatic mutation (blue to pink or colorless). The periods of maximum sensitivity varied with exposure and the position of hairs on the stamen. Somatic pink mutations were induced at a rate of 9·11 × 10 −4 pink mutant events per meristematic hair cell per R. Colorless mutant events were induced at much higher rates (1·3–3·0 times more colorless events than pink events). However, some of the colorless cells were considered to be genotypically pink cells or those derived secondarily from pink mutant events. The frequencies of the hairs which had suffered complete or partial loss of reproductive integrity (LRI) were determined for each exposure, utilizing induced somatic mutations as markers. Complete LRI and losses greater and less than 50 per cent occurred in 0·7, 2·1 and 3·6 per cent of stamen hairs, respectively, after 69 R, and 27·9, 27·7 and 15·9 per cent of hairs, respectively, after 282 R. It was concluded also that the irradiation evidently induced lengthened cell cycle times as well as complete (immediate) and delayed LRI. The lengthened cell cycle time and delayed LRI can explain the occurrence of hairs with partial LRI. The occurrence of morphologically abnormal cells was found to be positively correlated with the LRI but a variable fraction of stunted hairs had no apparent abnormality in the apical cell.