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Wheat Information
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Number 72: 99-101 (1991)
Chromosome
mapping of ribosomal RNA genes in Triticum spelta by
in situ hybridization
M.Yamamoto1) and Y. Mukai2)
1) Department of Life Science, Kansai Women's Junior College,
Kashiwara, Osaka 582, Japan
2) Department of Biological Sciences, Osaka Kyoiku University, Ikeda,
Osaka 563, Japan
Introduction
We report here on physical mapping of ribosomal RNA genes (rDNA)
in Triticum spelta, one of hexaploid wheat (2n = 42,
AABBDD) by in
situ
hybridization. The origin of spelta wheat is discussed in
terms of in
situ
hybridization patterns of rDNA.
Materials and Methods
Three strains of T. spelta were used in the present study.
Wheat 18S-26S rebosomal RNA gene and the repeated DNA sequences from
Ae. squarrosa (pAs1) were used as probes. The latter probe was
used for the identification of wheat chromosomes (Rayburn and Gill
1986). The details of the procedure for cytological preparations,
in
situ
hybridization using biotinylated probes, and detection of
hybridization sites are as described by Mukai et al (1991).
Results and Discussion
In
situ
hybridization analysis using biotin-labeled rDNA probe indicated that
four pairs of chromosomes carried Nor loci in T. spelta
(Fig.
1a). The
identification of chromosomes 1B, 6B, 5D and 1A was made by double
labeling with rDNA and pAs1 probes. The latter clone reveals a small
hybridization site on the satellite and on intercalary site of
hybridization on the short arm in chromosome 6B (Fig.
1b). Chromosome
5D was also observed to have four sites of hybridization with pAs1.
One site was located not on the satellite but on the terminus of the
short arm and three intercalary sites of the long arm
(Fig.
1c). No
hybridization site was observed on chromosomes 1B and 1A. Therefore,
the Nor chromosomes were confirmed as 1A, 1B, 5D, and 6B. The signal
intensity was 1B>6B=5D>>1A. In chromosome 1B, most of the
highly condensed rDNA signal was distributed in the proximal end and
the remainder in the distal end of the secondary constriction joined
by a middle faint signal. In chromosome 6B, condensed rDNA was
distributed evenly at each end joined by diffuse rDNA. In chromosome
5D, condensed rDNA was found on the satellite. In most cells, a part
of rDNA on chromosome 5D was dispersed, showing genetic activity of
ribosomal RNA genes. Chromosome 1A showed a dot-type signal at the
terminal end of the short arm. None of the rDNA on chromosome 1A was
found dispersed but remaind condensed.
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