Effects of gamma-ray irradiation on the growth of calli in Nicotiana species.

Abstract

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 irradiatlon 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.