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Results and
Discussion
Expermental results revealed that the frequency of cells with
anaphase bridges as well as fragments increased with an increase in
radiation dose (Table
1). The number of
cells with bridges was more than those with fragments. Post treatment
with GA3 reduced the frequency of anaphase bridges as well
as fragments. The difference between the control and GA3
treated cells was more at higher radiation doses.
Mitotic index in the control decreased with an increase in the
radiation dose, though at 10 kR there was some stimulatory effect
resulting in an increase in the mitotic index (Table
2). This was also
reported by Khanna (1990) in wheat. According to Simonis (1966),
radiations are capable of considerably changing the type of
information of certain DNA molecules. This may be the reason for the
increase in mitotic index at lower doses and a decrease at higher
doses. GA3 increased the mitotic index, the increase being
more in irradiated seeds.
Seedling height responded to GA3 as well as to gamma
radiation. It decreased with an increase in radiation except at 10 kR
which stimulated seedling height. GA3 also increased
seedling height, the maximum increase being at 10 kR. Stimulation in
seedling height may be due to faster tell division, change in auxin
balance or enhancement in enzyme activity. (Table
3)
Peroxidase activity increased with seedling growth from 0-6 days of
germination of the seed (Table
4). An increase
in radiation doses decreased enzyme activity except at 10 kR where it
was more than control. Kuzin (1980) suggested that irradiation at
lowaer doses often induced the production of small quantities of
radiotoxins with resulted in stimulation, on growth and development.
Peroxidase activity was more in GA3 treated seeds.
This study shows that post-treatment with very low concentrations of
GA3 decreased the frequancy of anaphase aberrations due to
gamma irradiation in triticale. Similar protective effects of
GA3 could also be seen on seedling growth and mitotic
index. Peroxidase activity also increased in GA3 treated
seeds.
Chemicals such as aminothiols, that are known to give protection
against radiation damage, must be present at the time of irradiation
and are effective only as pre-treatments. These may act either as
free-radical scavengers or by causing anoxia in the system (Bacq and
Alexander 1961, Alper 1979). Gibberellic acid enhances metabolic rate
(Jones 1973) and increases peroxidase activity (Thakral 1979, Jain et
al 1980). Our results also show that GA3 enhanced
peroxidase activity. Due to higher respiratory activity in
GA3 treated seeds, a local state of relative anoxia may be
created in the cell so that there is low cell damage (Alper 1979) or
due to enhanced peroxidase activity, surviving peroxy radicals may be
eliminated such that the resultant detectable damage is less. Another
possibility is that gamma radiation caused potential lesions (Bacq
and Alexender 1961) which are normally converted to
real cytological damage on imbibition of seed, and are eliminated due
to a high metabolic rates of GA3 treated seeds.
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