Repetitious Production of Similar Karyotypes in Different Plants of Haplopappus gracilis, an Annual Asteraceae, Following Exposure to Ionizing Radiation

Abstract

Following exposure to X-rays or reactor radiation at the early germinating stage, seedlings of Haplopappus gracilis (Nutt.) Gray were inspected for karyotypic changes in the meristems of lateral roots 2 months later. Among 210 plants studied in total, 12 were carriers of aberrant karyotypes in the root systems. One of them was a whole-body variant of spontaneous origin, showing a complete change of karyotype not only in the root system but also in the shoot system. The remainders were mosaics, showing a complete karyotypic change in one or more lateral roots but not in the whole root system. Of the 11 cases of aberrant karyotypes detected as inter-root mosaics, 5 were unique to the respective plants, each characterized by a specific kind of non-reciprocal translocation, reciprocal translocation or complex exchange; 2 were commonly characterized by a complex exchange; 3 were by a non-reciprocal translocation; one was characterized by a fragment chromosome accompanied with a shortened chromosome and was not distinguishable from the aberrant karyotype of spontaneous origin. These results support the conclusion that the chromosomes of H. gracilis possess the plasticity to rearrangements after irradiation. The repetitious occurrence of specific rearrangements in different plants and the recovery of fragment-bearing karyotype are discussed as suggestive evidence for the existence of preferential sites for breakage and rearrangement in H. gracilis genome.

Cytogenetical Evidence for Latent Centromeres and Reactivation in Chromosomes of Haplopappus gracilis (Asteraceae)

“…1A). These findings are consistent with and confirm data in previous papers (Tanaka 1967, Yonezawa 1981a, Ikeda 1987, Hanmoto et al 2003. Fig.…”

“…Out of 160 progenies, only one plant (designated as 78-465) possessed 2nϭ5 chromosomes. The other two plant materials, X18-38 and X18-49, were found growing among 133 plants from the achenes irradiated by X-rays just at the time of germination and had 2nϭ5 with a fragment-like chromosome (Hanmoto et al 2003).…”

“…The preparation was the same as previously reported (Yonezawa 1981a, Hanmoto et al 2003: Root tips were pretreated with 0.002 M 8-hydroxyquinoline solution for 90 min at 18°C or 0.1% colchicine solution for 60 min at 20°C followed by fixation in 45% acetic acid solution for 15 min at 5°C. The tips were then macerated in a mixture of 1 N HCl and 45% acetic acid (2 : 1) for 15 s at 60°C.…”

“…We previously reported the karyotypes of 2nϭ5 observed in the plants irradiated by X-rays and pointed out that the extra centromere in the 2nϭ5 complement might be derived from the reactivation of the suppressed centromere in the chromosome 1 in H. gracilis (Hanmoto et al 2003).…”

Interstitial Telomere-like Repeats in the Haplopappus gracilis (Asteraceae) Genome Revealed by Fluorescence in situ Hybridization

“…Ames and Mitra (1968) and Hanmoto et al (2003) reported that the subdistal positions of the long arms in both 1g and 2g chromosomes of H. gracilis are the breakage points by maleic hydrazide treatment and by ionizing radiation, respectively. These points correspond well to the ITR sites revealed by FISH in the present study.…”