Effects of X-ray dose fractionations with various intervals in inducing somatic mutations in the stamen hairs of Tradescantia clone KU 9.

Abstract

The effects of X-ray dose fractionations in inducing somatic mutations were studied in the stamen hairs of Tradescantia clone KU 9 heterozygous for flower color (blue/pink). Young inflorescence-bearing shoots with roots were prepared, and were exposed to X rays acutely. A dose-response regression line with a slope of 1.454 on a log-log graph was obtained for single acute X-ray doses of 0.255 to 1.03 Gy, and it showed that somatic mutation frequency increased curvilinearly with increasing X-ray dose. When 1.00 to 1.15 Gy of X rays were fractionated into two acute doses of about halves given with intervals of 5 to 120 min, decreases in induced mutation frequency were observed. The mutation frequencies induced by the fractionated doses with intervals of 5 and 10 min were not significantly different from those expected for the total single doses. However, the mutation frequency decreased significantly at 5% level with 20-and 30-min intervals, and decreases were highly significant at 0.1% level when the interval was prolonged to 40 to 120 min. The results obtained indicate that the interaction between the first and second doses began to reduce between 10 and 20 min later, and disappeared by 60 min later. That is, the DNA and/or chromosomal breaks induced by the first dose began to be rejoined (repaired) or healed between 10 and 20 min later, and all of them were rejoined or healed by 60 min later, losing their abilities to interact with the DNA and/or chromosomal breaks induced by the second dose.

Dicentric chromosome bridges in root tips and micronuclei in pollen tetrads induced by X rays and maleic hydrazide in Tradescantia clone BNL 4430.

“…The present value is rather closer to 1.249 obtained for X ray-induced dicentric bridges (Fig. 1), and also to those determined earlier for X ray-induced somatic pink mutations in stamen hairs, i.e., 1.252 to 1.390 in clone BNL 4430 (Shima and Ichikawa, 1994, 1997Xiao and Ichikawa, 1995) and 1.237 to 1.454 in other clones, KU 27 (Sanda-Kamigawara et al, 1991;Ichikawa et al, 1993), BNL 02 (Sanda-Kamigawara et al, 1991 and KU 9 (Sakuramoto and Ichikawa, 1996). The present slope value for X ray-induced micronuclei in pollen tetrads at earlier stage close to those for X ray-induced somatic mutations suggests that the micronuclei observed were mostly the results of single chromosomal breaks.…”

“…Especially, newly developed use of young inflorescence-bearing shoots with roots of clone BNL 4430 cultivated in the NSC growth chamber (Shima and Ichikawa, 1994, 1997Ichikawa et al, 1995;Xiao and Ichikawa, 1995) can supply a much larger number of samples per space than using potted plants or cuttings, assures a high degree of reappearance, and decreases significantly the spontaneous mutation frequency (Shima and Ichikawa, 1994;Ichikawa et al, 1995). The young inflorescence-bearing shoots with roots of clone KU 9 cultivated in another NSC facility have also exhibited a significantly lower spontaneous mutation frequency (Sakuramoto and Ichikawa, 1996). The lower background level and high degree of reappearance are two other important assets of the Tradescantia stamen-hair system, especially in comparison with the micronucleus assay.…”