Chromosome Studies in Chionographis (Liliaceae)

I. On the holokinetic nature of chromosomes in Chionographis japonica Maxim

Abstract

Mitosis was studied in the root-tip cells of Chionographis japonica Maxim. (2n=24; Liliaceae).
Mitotic chromosomes of this species were found to show several unusual characteristics in the appearance and behavior; namely, the chromosomes at metaphase and anaphase do not show any distinct morphologically visible constriction, and the sister chromatids in mitotic anaphase separate quite in parallel. These characteristics are, apparently, quite different from the ordinary monocentric type of chromosomes. In order to make clear the motile system of the chromosomes, the X-ray irradiation experiments were carried out. Many fragments of chromosomes were produced by the irradiation. The ratio of the chromosome-aberrant cells fixed on 10th day after irradiation (Lot no., R-4) was 82.7%, and this ratio was almost as high as the ratio of the aberrant cells obtained in lst day collection (Lot no., R-1) after irradiation. In spite of these high occurrences of the aberrant cells, chromosome separation was quite normal in most of the anaphase and telophase cells examined, and no micronucleus was detected. In many anaphasic cells, minute fragments could be observed to separate quite normally, just like as the normal chromosomes. Therefore, most fragments of chromosomes could survive in the subsequent generations. All these observations seem to suggest that the chromosomes of Chionographis japonica are of the holocentric ones.