THE USE OF INDUCED SOMATIC MUTATIONS TO STUDY CELL DIVISION RATES IN IRRADIATED STAMEN HAIRS OF TRADESCANTIA VIRGINIANA L

Inflorescences of Tradescantia virginiana L. HV Purple Dome (2n=24), heterozygous for flower color, were exposed to 100 to 500R of 137Cs gamma rays over a 16-hour period. Stamen hairs from both irradiated and unirradiated flowers were observed daily for 26 days after irradiation, and number and position of the somatic mutations (blue to pink) induced in the stamen hair cells were recorded. Somatic mutations were induced at a rate of 4.75×10-4 mutant events per meristematic hair cell per R in the essentially single-meristematic-cell system. Using the mutant cells as markers it was estimated that the gamma rays evidently induced mitotic delay, lengthened cell cycle time and an impairment of normal reproductive integrity. The effect increased with increasing exposures. The average daily increase in number of hair cells per terminal mutant event varied from 2.6 after 100R to 0.56 after 500R. The average mitotic cycle times estimated also varied from 17.5 hours after 100R to a maximum of 80 hours after 500R, an increase of approximately 4.6-fold in cycle time. However, the length of the mitotic cycle approached the control rate even after 500R after about 15 days