Configurations Taken by X-ray Induced Heteromorphic Chromosome Pairs at M₁ in the PMCs of Trillium kamtschaticum PALL

Abstract

1) It was shown with the aid of x-ray irradiation test that a) premeiotic mitosis in the anther of T. kamtschaticum is finished at the end of September, or about five months prior to MI in the PMCs, and b) chromosome splitting in meiotic prophase in the PMCs takes place in late October.
2) Sensitivity changes to x-rays during early meiotic prophase in the PMCs of this plant was investigated to show that the PMCs of the materials taken from Toyoni population became quite labile to the irradiation in mid October. The lability seems to concern, examined with the materials taken from Akkeshi population, with modifications of restitution process of the broken ends produced in chromosomes by the irradiations.
3) Four types of aberration: B'' (chromosome breakage), T'''' (chromosome translocation), T''' (chromosome-chromatid translocation) and T'' (chromatid translocation) were distinguished in bivalents at M_I. The translocations increased in proportionate to two power of x-ray dosage, while the breakages were produced approximately in direct proportion to it.
4) The heteromorphic chromosome pairs induced by irradiation which was given before the prophase splitting of chromosomes in the PMCs, performed, in majority of the cases, reductional opening-out of chromatids at diplotene.
5) Configurations which were regarded by Matsuura as supporting equational opening-out of chromatids were extremely rare. It was suggested that these rare configurations may possibly be the ones derived from T''' and T'' which occurred between homologous chromosome arms. On the other hand configurations supporting the chiasma theory were often taken by the heteromorphic pairs.