II. 28. Mutagenic effects of HA in barley through treatments at different periods in the S-phase.
R. M. Singh and J. Singh, Dept. of Genetics and Plant Breeding, Faculty of Agriculture, Banaras Hindu University, Varansi--221005, India.
The mutagenic effects of hydroxylamine (HA) treatment for 1 hr. duration during S-phase of the cell cycle in barley var. K572/11 have been investigated. Seeds were soaked in distilled water for 1 hr. and then grown at 22°C for 16-20 hrs.; the duration of S-phase. These seeds were then treated with 0.08 M solution of HA (prepared in phosphate buffer, pH 6.5) for 1 hr. at 16, 17, 18, 19, and 20 hrs. of soaking falling in early, middle, and late S-phase. Treated seeds were washed in running tap water for 4 hrs. and were sown in field along with control. Seeds from each M1 plant were harvested separately to raise the M2 generation. The M2 generation was grown as single plant progeny and the population was scored for chlorophyll mutations (Table 1). It is evident from Table 1 that the frequency of total chlorophyll mutations was almost similar irrespective of the treatment timing during S-phase except at 17 hrs., where the frequency was somewhat higher. However, some variation occurred in the chlorophyll mutation spectrum. The frequency of Albina was about 3-4 times greater than Viridis, Xantha, and Chlorina, whereas that of Tigrina was the lowest. Albina and Viridis occurred in all the treatments, indicating no differential replication of genes controlling these characters. Xantha appeared after 1 hr. and Striata after 2 hrs. but continued till end of the S-phase, whereas Dark Xantha were restricted to a very narrow period of S-phase, i.e., from 17 to 18 hrs. The majority of Chlorina occurred in early and Tigrina in the middle S-phase. These observations indicate differential response of genes to HA treatment and may be related with their replication time during S-phase of the cell cycle.
