Agriculture Reference
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The later plantlet—27 h after soaking was characterized by the more high frequen-
cy of rearrangements than upon the fi xation—12 h in fi rst plantlet—24 h. After 36 h
after soaking of seeds, the frequency of rearrangements increased again in comparison
with last fi xation (27 h after soaking of dry seeds) (see a Figure 24.1).
All rearrangements were of the chromatid type. They arise during the synthesis of
DNA.
On the basis of these facts, we conclude that mutagen was presented in cells during
all periods of fi xation, affecting chromosomes after their passing to the DNA synthesis
and remained in cells 24, 27, and 36 h after plantlet, in spite of washing of seeds by tap
water from the phosphemid. Increase number of rearrangements under fi xation 2, 6, 9,
and 12 h after arising of plantlet in 24 h after treatment indicates the heterogeneity of
phase of G
1
in dry seeds. It is not a “delayed effect” of chemical mutagens, typical for
asynchronous population of cells, when chemical mutagens do not cause rearrange-
ments of chromosomes at G
2
or G
1
of mitotic cycle. In our experiments, the growth of
number of the rearrangements in plantlets can result from the storage of mutagen in
cells and gradual transmission of cell cycle from the G
1
stage to the synthesis of DNA.
Increase of number of rearrangements in the plantlet after 36 h can be explained also
by the lack of synchronization of passage of cell cycle to the synthesis of DNA by dif-
ferent cells in the presence of mutagen. Table 24.3 and a fi gure show the mitotic activ-
ity (number of the mitoses in plantlets) at different periods after plantlet or of fi xation.
TABLE 24.3
Mitotic activity of cells in plantlets of
Crepis capillaris
after treatment of air-
dried seeds with phosphemid at a concentration 2 × 10
−3
M. Harvest 1967. Analysis 1968
Time from the begin-
ning of treatment (h)
Time from plantlet to
fixing (h)
Plantlets, number
Total
With mitoses
(%)
April
24
3
57
24
42.1
-
6
56
32
57.1
-
8
54
36
66.7
27
3
47
16
35.5
-
5
19
12
65.0
On average
233
120
51.5 ± 3.28
June
24
3
38
5
13,2
-
6
28
16
57.1
Time from the begin-
ning of treatment (h)
Time from plantlet to
fixing (h)
Plantlets, number
Total
With mitoses
(%)
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