Variation in Nucleolar Number among Varieties of Cultivated Rice

Abstract

1. The number of nucleoli newly formed in somatic telophasic nuclei was observed in a number of rice varieties from various Asian countries.
2. In some varieties, the number of nucleoli varied from two to four from cell to cell, while in other varieties two nucleoli were found in all cells. The former and the latter varieties may correspond to the so-called “quadrinucleolar” and “bi-nucleolar” types.
3. About two thirds of the “Continental” varieties and a half of the “Tropical-Insular” varieties were of quadri-nucleolar type. In the former, the mean number of nucleoli ranged from 2.2 to 3.6.
4. All Japanese lowland Varieties were of bi-nucleolar type, while both bi- and quadri-nucleolar types were found in different proportions in other regions.
5. It was mentioned that rice might have two pairs of nucleolar chromosomes, and the nucleolus-forming power of the second pair being relative to the first, as shown by the mean number of nucleoli, might vary continuously among varieties.