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Materials and Methods
Three accessions of Roegneria tsukushiensis (Honda) 13.R.
Lu et J.L. Yang (2n=42, SSHHYY) used in this study were collected
from Yaan and Yibin, Sichuan Province respectively. Two accessions
of Psathyrostachys huashanica Keng (2n=14,
NhNh) were collected from Mt. Huashan, Shaanxi
Province, China. All these accessions were cultivated at Triticeae
Research Institute, Sichuan Agricultural University in 1990.
Hybridization was made by pollinating hand-emasculated spikes of
R. tsukushiensis with pollen of P. huashanica.
Three F1 seeds were germinated in petri-dish, then
transplanted into pots.
For cytological study, young
spikes of the three F1 hybrids derived from three
different accessions of R. tsukushiensis crossed with one
accession of P. huashanica and their parents were fixed
in Carnoy's fluid for 24 hours. They were transferred to 70% ethanol
and stored at 4oC. Microsporogensis was studied on slides
prepared by standard acetocarmine squashing.
Results and Discussion
The intergeneric F1 hybrid of R. tsukushiensis
with P. huashanica is theoretically expected to
have 28 chromosomes. Chromosome numbers counted at metaphase 1 of the
pollen mother cells (PMCs) met the expectation (Fig.
1-1). The meiotic
data indicated that R. tsukushiensis shared no common genome
with P. huashanica (Sun et al. 1993a).
Abnormal microspore
formation was observed in microsporogenesis of this intergeneric
hybrid. Chromatin materials were transferred through conjugation
opening among neighbouring cells from the time before meiosis until
the young pollen grains stage (Fig.
1-2~7). The
amount of chromatin materials transferred varied among cells. The
process of chromatin migration among cells causes coenocytes,
multiplication and diminution of chromosomes greatly, and variation
in cell size. Fig.
1-2 shows PMC a
and PMC b in contact with each other and forming a fused big opening.
The numbers of anaphase chromosomes in these two cells are unequal.
Anaphase chromosomes also show non- synchronous separation. In cell
a, there are 9 anaphase chromosomes and 7 chromatids; in cell b there
are 2 anaphase chromosomes and 3 chromatids. In Fig.
1-3, two PMCs at
chromonema stage contacted each other, chromonemata migration takes
place through the conjugation opening. In Fig.
1-4, cell a has
two separate synchronous nuclei at chromonema stage; cell b with
small cell size has only one chromosome and two chromatids. The
chromosome diminution might be caused by uneven distribution of
chromosomes before cytokinesis of two conjugated PMCs as shown in
Fig.
1-2. After
cytokinesis, this kind of small size PMC has occurred as a result a
diminished number of chromosomes. In cell c, two chromonema stage
nuclei are mixed together. A nucleus has twice as many chromosomes as
the usual one. Polyploidy or aneuploidy will occur. A bud-like
structure has a micronucleus (Fig.
1-4). The young
pollen grains are shown in Figures
1-5~7. We can see
that the resting stage nuclei are just migrating through the
conjugation opening between two young pollen grains.
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