[en] Haploid and diploid calli of Nicotiana glauca (n = 12) and N. langsdorffii (n = 9) together with dlploid calli of N. tabacum (n = 24) cv. Bright Yellow which were taken as control were ex-posed to various doses of ⁶⁰Co gamma rays at 7 days and 10 days after incubation. Calli were subsequently weighed for a period of 12-14 days after radiation (19-24 clays after incubation) and the effect of irradiation on the growth was studied. A sigmoid curve was observed for the growth rate as well as for the growth pattern. The radiosensitivlty were estimate.d on the basis of the following different two criteria: 1) the difference in the diploid callus volumes at 12 or 14 days after irradiation and at the time of radiation, 2) the growth rate of diploid and haploid calli during these period. In 2 species except in N. langsdorffii, calli irradiated ten days after incubation (at the beginning of the actively growing stage) were more sensitive to gamma irradiation than calli lrradiated seven days after incubation (at a relatively slow growing stage). Each species had its own distinctive color before irradiation; golden yellow, green and yellow green for N. glauca, N. langsdorffii and N. tabacum, respectively. The color of some of the calli tended to darken with increasing irradiation doses. When the rate of increase of the irradiated calli to that of the unlrradiated ones was used as an indicator of radiosensitivity, there was a significant difference in the radiosen-sitivity of the calli among the species: N. tabacum was more sensitive followed by N. glauca and N. langsdorffii, which was the least sensitive. On the other hand, when the curve of the increase of the growth rate was used as the criterion of radiosensitivity, N. langsdorffii appeared to be more sensitive than N. tabacum and N. glauca. Haploid calli were more radiosensitive than diploid ones in N. glauca, but no significant difference was observed between them in N. lanegsdorffii. (author)

No abstract available

[en] The effect of irradiation on the survival rates and embryonic development of Brassica pekinensis RUPR. (Varieties; Kashin, Kohai 65 nichi and kairyochitose) was investigated. The purpose of this study was to seek ways of increasing the survival rates of embryos such as B.oleracea obtained through embryo culture techniques after irradiation doses affecting seed fertility and germination, for the purpose of increasing mutation rates. Embryos at different developmental stages ranging from the globular to the early heart stages were irradiated with 20 KR of gamma rays at the daily rate 0L 20 KR or 10 KR (Fig.1 and Table 1). The embryos were excised from ovules 4 to 10 days after irradiation and cultured on White's medium. The shooting and rooting rates on the 34th day of culture were higher at the dose of 10 KR/day than 20 KR/day and were lower when the materials were irradiated at the young embryonic stage (Table 3). Varietal differences in the shooting and rooting rates were also observed. The irradiated embryos survived mainly in the state of callus. It was concluded that the embryo culture technique was successful when applied to irradiated embryos excised at the young embryonic stage and that the technique affected B.pekinensis less than B.oleracea

No abstract available

[en] The in vitro adventitious bud technique was used in conjunction with gamma irradiation for the induction of mutation in red pepper. The twelve-day-old seedlings were irradiated by gamma radiation at the exposure doses of 0, 0.5, 0.75, 1.0 and 1.25 krad delivered at the dose rate of 5 krad/h. After irradiation adventitious shoots were induced from the excised cotyledons. The shoots were rooted and the obtained plantlets were grown under greenhouse conditions until maturity. No variant segregation was observed in control plants from both seeds and non-irradiated cotyleclon explants whereas visible variants were found among the M₁ plants regenerated from irradiated cotyledon explants at the frequency of 4.4%. The variation spectrum was consisted of plant type, leaf, flower and fruit variation. Rate of chimerism based on visual characters was considerably high, indicating the multicellular origin of adventitious shoot. A number of variants were recovered in the immediate gamma ray treated generation (M₁). Most of the variant characters obtained were transmitted to the M₂ progeny and were considered as mutants. Some of the characters were bred true and many were segregated. Most of the mutated characters were stabilized in the M₃ generation. Three types of the variant pheonotypes were lost and the causes were discussed. (author)

[en] In the case of irradiation of seeds of self-pollinated and disomic plant materials, the frequency of mutated plants appearing in the M₂ generation divided by the Mendelian ratio is an index, as proposed by Gaul (1960), that enables the direct estimation of the mutation rate, representing the ratio of the number of mutated cells to the number of survived cells after treatment of mutagen. In the case of chronic irradiation of growing plants throughout the entire life cycle from germination to maturity, on the other hand, the mutations induced at the stage preceding the differentiation of the male and female organs appear at the M₂ generation, the but mutations induced after this critical time are observed in the M₂ plants in the heterozygous condition and are detected only at the M₃ generation. Therefore, the mutation rate can not be correctly estimated only on the basis of the frequency of mutants either in the M₂ or M₃ generation. A new method for the estimation of the mutation rate by combining the data of the frequency of mutants and the M₂ and M₃ generation, which is comparable to Gaul's method for seed irradiation, is proposed. Application of this method to the data of acute and chronic gamma-ray irradiation of growing barley revealed that a much higher mutation rate was observed after irradiation at a higher daily exposure rate, when the plants were treated with the same accumulated dose

[en] Two techniques were useful in overcoming hybrid inviability between N. repanda and N. tabacum. These techniques combine gamma-ray irradiation to pollen or to egg cells (in ovules) with in vitro culture of fertilized ovules. When in vitro culture of fertilized ovules from in situ hybridization of N. repanda x N. tabacum was combined without gamma-ray irradiation to pollen or to egg cells (in ovules), all of the resulting seedlings developed chlorosis and died. Furthermore, in the case of in situ hybridization of N. repanda x N. tabacum with gamma-ray irradiated N. tabacum pollen, no viable seeds were obtained. By using both techniques, combining gamma-ray irradiation to N. tabacum pollen or to egg cells in (N. repanda ovules) with in vitro culture of fertilized ovules, we were successful in obtaining flowering hybrid plants. Thus, it appears that it may be possible to overcome hybrid inviability to a certain extent using both the pollen irradiation technique and the egg cell irradiation technique, i.e., gamma-ray irradiation to pollen or to egg cells (in ovules) before pollination and in vitro culture of fertilized ovules. (author)

[en] Radiosensitivity of barley varieties as expressed by callus growth was examined after exposure of seeds to gamma-rays and transfer of mature embryos detached from seeds or whole seeds onto medium for the initiation and growth of callus. Marked differences in the value of D₅0 about 7-fold at maximum were observed among the varieties employed (Figs. 1 a and b). Particularly all the naked varieties used showed much lower values of D₅0s than the covered ones (Table 1). These results correspond to the level of radiosensitivity expressed by seedling growth after seed irradiation (Figs. 2, 3). A major gene (rs) on chromosome I which has recently been found to control the latter radiosensitivity seemed to exert its effect on the radiosensitivity measured by the callus growth. When calli initiated from seeds were irradiated three days after inoculation on agar medium, the value of D₅0 for callus growth decreased markedly from 44 kR in seed irradiation to 5 kR in callus irradiation for the covered variety, while the change in the value of D₅0 was slight, changing from 7 to 3 kR for the naked variety. The difference in the value of D₅0 was not large, but still significant (Figs. 4 a, 4 b). The relationship between the value of D₅0 for seedling growth in the case of seed and seedling irradiation and that of D₅0 for callus growth after callus irradiation varied considerably with the varieties. (author)

No abstract available

[en] The combination of 2 techniques, i, e., pollination after the destruction of chromosomes in pollen grains with ionizing radiations and in vitro culture of crossed ovules, was applied to interspecific hybridization between N.repanda and N. tabacum in order to investigate the possibility of overcoming hybrid inviability in the cross-combinations. By using these techniques, it became possible to obtain aneuploid hybrids, which had never been reported previously