Effects of temperature and irradiation time upon mutations
induced by radiations
S. MATSUMURA
National Institute of Genetics, Misima, Japan
Dormant seeds of Triticum monococcum flavescens were exposed to
X- and gamma-rays at the dosage 10 and 20 kr. The growth of seedlings,
the single-spike fertility and chromosome aberrations of treated plants
(X1) and the chlorophyll mutations in X2 were compared
for acute and chronic irradiation. At acute irradiation with X- and gamma-rays
treatment was given either immediately before sowing or the irradiated
seeds were kept for 30 days in storage at room temperature (about 20C)
or at 5C. At chronic gamma-irradiation with 60Co the treatment
lasted 54 days. Also, the effect of Beta-radiation by 32P was
examined for comparison.
The data are shown in the table. The relation between the inhibition of
seedling growth and dosage, temperature in storage and irradiation time
coincides roughly with the relation between the percentage of induced
sterility and all those conditions. X- and gamma-irradiations were far
more effective at 20 kr than at 10 kr. In the case of 30
day storage, gamma-rays inhibited the growth of seedlings and reduced
the fertility more than X-rays, while irradiation applied just before
sowing showed the reverse relation. It was found further, especially with
gamma-rays, that low temperature had the strongest inhibiting effect.
At 10 kr acute gamma-irradiation was more effective than the chronic
one, while at 20 kr the reverse relation was observed.
The frequency of ears with chromosome aberrations in X1-plants
was strikingly higher at 20 kr than at 10kr. In most of
the cases of induced chromosome aberrations (4)+5II, often
6II+2I, (6)+4II, (4)+(4)+3II
or (4)+4II+2I and seldom 1III+5II+1I
or asynaptic 14I have been observed. The effect of gamma-rays
was generally stronger than that of X-rays. Also, irradiation just before
sowing and 30 day storage at low temperature produced more chromosome
aberrations than storage at room temperature after irradiation. On the
other hand, the effect of chronic gamma-irradiation, because of two-hit
aberrations, such as translocation, are limited in time.
The frequency of head progenies with chlorophyll mutations in the X2-generation
increased with the increase of radiation dosage. Because of the small
number of observed head progenies, due to a lower survival rate, the results
with 20 kr irradiation were insufficient. But they were roughly
in accord with the observations of chromosome aberrations.
The effects of Beta-irradiation were unexpectedly slight. It was found
from another experiment with seed absorption of 32P-solution
that the actual dosage of Beta-rays was very low.
(Received April 24, 1958)