BGN 10: Forward and back mutations at the ligule-less (li) locus of barley BARLEY GENETICS NEWSLETTER, VOL. 10, II. RESEARCH NOTES
Konishi, pp. 36-38

II. 16. Forward and back mutations at the ligule-less (li) locus of barley.

T. Konishi. The Ohara Institute for Agricultural Biology, Okayama University, Kurashiki, 710 Japan.

In barley dormant seeds, cells in the shoot apical meristem stay in the G1 stage, and the first DNA synthesis takes place with a partial synchronization after soaking of seeds (Tatara and Yamaguchi 1973). Therefore, mutagen treatments for a short period at different stages of interphase will be useful for achieving some specificity in the type of mutations (Yamaguchi et al. 1975). The present investigation was undertaken to induce forward and back mutations at li locus by mutagen treatments at different stages of cell cycle in barley embryos.

Table 1. Ligule-less and chlorophyll mutations by EMS treatments (300 mM, 1 hour) after different durations of presoaking at 20°C.

As to forward mutation, two series of experiments were conducted in different years to obtain li mutants from a six-rowed naked cultivar, Akashinriki, with normal ligules and auricles. The procedures of the two experiments were the same, but different in the duration of soaking. The seeds were prepared to be as uniform as possible in size (2.5 - 2.8 mm in thickness) and water content (12%), and they were soaked in distilled water during different times as shown in Table 1. After presoaking, the seeds were treated in 300 mM EMS solution for one hour, and washed in running water for 8 hours. These treatments were made at the same temperature of 20°C. M1 plants were grown in a greenhouse for preventing outcrossing with other genotypic pollens, and one spike from each of the M1 plants was harvested. Thirty progenies per M1 spike were raised in a nursery, and the appearance of li mutants was examined at M2 seedling stages. According to Table 1, four li mutants appeared in an M1 spike progeny of 15-hour presoaked plot of the first experiment, and two li mutants were observed in another progeny in 16-hour presoaked plot of the second experiment, respectively.

Table 2. Reverse mutation at li locus by EMS treatments (300 mM, 1 hour) after different durations of presoaking at 20°C.

For the study of the reverse mutation to the normal phenotype with well-developed ligules and auricles, a li strain, Akashin li-1, derived from the original Akashinriki by EMS treatments was used. The li strain is isogenic to the normal variety except for the li locus, and known to be spontaneously revertible to the normal type with a low frequency (Konishi 1975). The seeds were treated with either EMS or BUdR using the same procedures as those mentioned in the previous experiments. Table 2 shows us that EMS treatment after 16-hour presoaking gave more than one revertant per M1 spike progeny, simply called here "multiple" event, which was thought to be the induced mutant. However, in the other treated plots and also in the control, there were found only single, not multiple, events which were produced by spontaneous reversions at li locus.

Table 3 indicates the result of BUdR treatments of the li strain, Akashin li-1. In this experiment, a multiple event with 4 revertants in an M1 spike progeny was also induced in 16-hour presoaked plot.

Table 3. Reverse mutation at li locus by BUdR treatments (2 mM, 1 hour) after different durations of presoaking at 20°C.

On the other hand, the highest frequency of chlorophyll mutations was found in the same 18-hour presoaked plot in each of these four experiments.

These results suggest to us that DNA synthesis may begin at or near li locus of chromosome 2, and become maximum in 18 hours after the beginning of presoaking of seeds.

References:
Konishi, T. 1975. Reverse mutation at the ligule-less locus (li) of barley. Barley Genetics Newsletter 5:21-23.

Tatara, A. and H. Yamaguchi. 1973. Timing of nucleic acid syntheses and mitosis in the first leaf meristem of germinating barley seed. Japan. J. Breed. 23:15-24.

Yamaguchi, H., S. Tano, A. Tatara, S. Hirai, K. Hasegawa and M. Hiraki. 1974. Mutations induced in germinating barley seeds by diethyl sulphate treatment at the interphase. "Polypoidy and Induced Mutations in Plant Breeding," IAEA, Vienna 1974:395-399.

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