13. A terminal deficiency in rice chromosome II
Zi-Xuan Wang1,
Yasunori Sukekiyo2, Atsushi Yoshimura and Nobuo Iwata
Faculty of Agriculture,
Kyushu University, Fukuoka 812, Japan
1) Present address: Rice
Genome Research Program, STAFF Institute, 446-1
Ippaizuka, Kamiyokoba, Tsukuba, lbaraki 305, Japan
2) Present address: Plantech
Research Institute, c/o MC-Research,
1000-Kamoshita-cho, Midori-ku, Yokohama 227, Japan
Many chromosome aberrants, including segmental deficiencies
have been obtained in rice by using irradiated pollen (Wang et al.
1988, 1991). We report here a terminal-deficiency of rice chromosome 11.
An la pseudo-dominant plant was found amongst
the 245 F1 plants derived from a cross between a stock homologous
for recessive genes lg (chromosome 4), st-I (formerly ws-I,
chromosome 6) and la (chromosome II) and irradiated Taichung 65.
The plant showed normal phenotype for lg and st-I, but mutant
phenotype for la, which was pseudo-dominant. The plant showed lazy
growth habit as the expression of the recessive gene la, had otherwise
normal plant morphology and had a seed-fertility of 40%.
Fig. 1. Somatic and pachytene chromosomes of an la pseudo-dominant
plant, a: somatic chromosomes, arrow shows a fragment chromosome, b: pachytene
chromosomes, arrow shows the centromere of the chromosome, which gives
single strand chromosome in terminal part of the long arm.
Somatic chromosomes of the plant were investigated using
the root tip cells. There were 23 chromosomes and 1 fragment chromosome
(Fig. la). In order to know the exact length of the missing chromosome
segment, we carried out pachytene analysis. It was found that about 75%
of the long arm of chromosome was missing (Fig. 1 b). Thus, this is a terminal
chromosome deficiency. Because the plant showed pseudo-dominant phenotype
for la which is known to be on chromosome 11, the missing chromosome
segment must include the region of la. Therefore, the deficiency
could be identified genetically to be in rice chromosome 11.
Chromosome behavior in meiosis was also examined
extensively using a large number of pollen mother cells (PMCs). More than
300 PMCs were examined. The results showed that only chromosome configuration
of 12 II was observed in metaphase I (MI), chromosome separations were
normal in anaphase I (AI) and anaphase II (AII), and no other abnormal
chromosome configurations, such as chromosome loop and chromosome laggards
were observed. The normal chromosome separation in meiosis in the plant
means that two kinds of microspores with n=12 and n=ll+l fragment were
formed. These results also suggest that the plant had no other chromosomal
rearrangements. In order to test transmission of the deficiency to progenies,
artificial pollination was made with the vegetatively-propagated la
pseudo-dominant plants as female parent. The selfed seeds of the pseudo-dominant
plants were also collected. A total of 404 f1 seeds and more than three
thousand selfed seeds from the pseudo-dominant plant were obtained during
three years (1988, 1989 and 1990). However, all plants from the F1
seeds, as well as from the selfed seeds, were normal in plant morphology
and seed fertility. These results indicate that the deficiency was not
transmitted to progenies either through pollen or the egg. Induced deficiencies
have been successfully utilized for centromere mapping and determining
the orientation of the linkage maps in many species (Singh 1993). Similarly,
the terminal deficiency reported here will be useful material for similar
studies in rice. We are now attempting to determine the orientation of
the RFLP linkage map of the chromosome 11 by using this terminal deficiency.
We thank Dr. N. Kurata, Rice Genome Research Program,
NIAR, Japan for her critical viewing of the cytological data.
References
Singh, R. J., 1993. Plant Cytogenetics. CRC Press, Boca Roton Ann Arbor,
London and Tokyo.
Wang, Z. X., N. Iwata, Y. Sukekiyo, A. Yoshimura and T. Omura, 1988.
A trial to induce chromosome
deficiencies and monosomics
in rice by using irradiated pollen. RGN 5: 64-65.
Wang, Z. X., N. Iwata, Y. Sukekiyo and A. Yoshimura, 1991. Induction
of chromosome aberrants in rice
(Oryza sativa L.)
by using irradiated pollen. J. Fac. Agr. Kyushu Univ. 36: 99-108.