Abstract:
The effect of presoaking seeds on sensitivity and mutation frequency in
rjce was studied. Treatments were given in 3 series le. with 3 doses of M«/JLJ
Each series consisted of 11 different periods of presoaking in range of 8 to 48
hours. Mutagenic effects were estimated in the M, and M. generations and interpreted.
Sensitivity to NMH increased with the length of presoaking and reached
a maximum at 32 hours. There was a decrease in sensitivity when presoaking
was extended beyond this period. The time specificity of the sensitivity peak
was independant of the dose of mutagen and the criteria adopted for its estimation.
The peak period of sensitivity corresponds to the time of DMA synthesis
in the initial cciis It appears that the first DMA synthesis in the initial
cells is responsible for the peak sensitivity at 32 hours presoaking.
The frequency of chlorophyll mutations increased with the length of
presoaking reaching a maximum at 40 to 44 hours. Conspicuous increase were
obtained during the periods 16 to 20 hours and 24 to 28 hours. The enhanced
efficiency during the 16 to 28 hour period can be attributed to the synchronisation
of treatment time with the 'S' phase of DMA synthesis. The spectrum
of mutations indicated predominance of albino, viridis and chlorina. Xantha
and tigrina were very rare and appeared only from 20 hours onwards. The
increase in relative per cent of albino with the length of presoaking and the late appearance of Xantha and tigrina were the characteristic features of the mutation
spectrum. The change in spectrum with different periods of presoaking
indicate scope for further efforts towards attaining mutation specificity.
