Karyological studies in haploid rice

II. Analysis of karyotype and somatic pairing

Abstract

In haploid plants derived from two Japanese varieties of rice, the morphology and behavior of chromosomes in somatic mitosis were observed. Low temperature treatment (4°-5°C. 20-24 hours) was applied for the root tips. Then, they were squashed and stained with 1% aceto-orcein. The results are briefly stated as follows:
1. Among the twelve chromosomes of haploid rice, four were of median, and the remaining eight of sub-median or sub-terminal types. Among both latter types, one chromosome with a secondary constriction (Fig. 2c, no. 2), one with a satellite (no. 8), and one with a secondary constriction and a satellite (no. 7) could be identified. In addition, the largest (no. 1) and the smallest (no. 12) chromosomes could also be identified. Thus, seven types of chromosomes were distinguishable in good preparations.
2. A tendency to somtic pairing was recognized at mitotic metaphase. The maximum pairing so far found consisted of four groups of two and one group of three chromosomes. The largest and the smallest chromosomes tended to pairing. The mode of somatic pairing was thus similar to that of secondary pairing in meiosis.
3. From the results of these observations, it was assumed that the karyotype of rice could be written as A^sm₁<(1)>+A^sm₂<(12)>+_csB^st<(2)>+C^sm₁<(3)>+C^sm₂<(4)>+2D^m<(5, 6)>+^t_csE^st₁<(7)>+^tE^st₂<(8)>+F^sm<(9)>+2G^m<(10, 11)>.