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Three other types of cytoplasmic polymorphisms were detected as
non-amplification of single fragments. One was recognized by
non-amplification of a 2.2 kbp fragment (A022,200) by a
primer OPA02. This polymorphism was detected in three NC hybrids with
D plasmon of Ae. squarrosa typica (C04), Ae.
squarrosa anathera (C19) and Ae. cylindrica (C28).
The same polymorphism was detected also in NC hybrids with M plasmon
(C05) and its related Mh (C06) and N (C07) plasmons. The
localization of A022,200 in the cytoplasmic genomes was
confirmed by RAPD- PCR analysis of the reverse hybrids, in which the
fragment A022,200 appeared after replacing their
cytoplasms by that of CS (Fig. 2B).
A022,200 was amplified in four NC hybrids with D2
plasmon of Ae. crassa 4x (C35), Ae. juvenalis
(C53), Ae. crassa 6x (C55) and Ae. vavilovii (C56).
A NC hybrid with the cytoplasm of Ae. ventricosa (C36) also
showed the amplification of this fragment, although its cytoplasm is
classified in D plasmon type Tsunewaki et al. 1996). It has been
suggested that Ae. juvenalis, Ae. crassa 6x and Ae.
vavilovii were derived from Ae. crassa 4x, and that
D2 plasmon of Ae. crassa 4x and D plasmon of Ae.
ventricosa evolved from D plasmon of Ae. squarrosa after
hybridization with Ae. comosa or Ae. heldreichii
followed by amphidiploidization (Tsunewaki 1995). It was therefore
suggested that nucleotide substitution(s) leading to the
amplification of A022,200 occurred in the cytoplasms of
Ae. ventricosa and Ae. crassa 4x after their evolution.
A second non-amplification, cytoplasm-specific polymorphism was
detected as a 1.7 kbp fragment by OPD05 (D051,700) in C16
with the A2 plasmon of T. monococcum. A third
non-amplification, cytoplasm-specific polymorphism of a 1.1 kbp
fragment by OPA13 (A131,100) was detected in male- sterile
C14 with the T2 plasmon of Ae. mutica. By contrast,
A131,100 was present in C13 with male-fertile T plasmon of
Ae. mutica, confirming the differentiation of these 2 plasmons
(Terachi et al. 1990).
The last polymorphism detected was amplification of ca. 0.6 kb
fragment by primer OPA01 (designated as A01600) unique in
C20 with the cytoplasm of Ae. longissima TL05. This
polymorphism was assigned to the nuclear genome because
A01600 was amplified in the reverse hybrid obtained after
replacing the cytoplasm with that of CS (Fig.
2C). Tsujimoto (1994) reported that one or a pair of the
maternal, gametocidal 5SL chromosomes are present in C20 and that
they are fully transmitted to their selfed and backcrossed progenies.
Root-tip chromosome counting confirmed the presence of this
chromosome, thus suggested that A01600 was derived from
the gametocidal chromosome present in this NC hybrid.
In conclusion, we could effectively detect plasmon-specific
polymorphisms using the NC hybrids of common wheat cv. CS having
cytoplasms from Triticum and Aegilops species.
Plasmon-specific polymorphisms detected were either specific to
single plasmons or mostly common to groups of phylogenetically
related plasmons. In combinations of these markers, D, T,
T2, Sb and A2 plasmons were
identified, although D plasmon of Ae. ventricosa was
exceptional. For the convenient identification of the cytoplasms in
the series of NC hybrids, a complete set of plasmon-specific RAPD
markers have to be selected by further study.
Acknowledgment
We express our sincere thanks to Prof. K. Tsunewaki, Fukui Pref.
University, for providing us with the original NC hybrids. The work
was supported in part by a Grant-in-Aid for Scientific Research (No.
0766007 to CN) from the Japanese Ministry of Education, Science,
Sports and Culture. Contribution No. 125 from the Laboratory of Plant
Genetics, Faculty of Agriculture, Kobe University.
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