Enhancement of the mutagenic effects of nitroso methyl urea in rice through alteration in the period of presoaking of seeds

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.