Effect of Environmental Conditions on the Frequencies of γ-Ray-induced Somatic Mutation in the Silkworm, Bombyx mori

Abstract

Various kinds of heterozygous striped (p^s/+^p) F₁larvae were irradiated with γ-rays at the dosage of 2, 000 R in the second or the third instar in order to investigate the effect of environmental conditions on the frequency of γ-ray induced white spots due to the elimination ofp^s-carrying chromosome fragment.
1. It was found that the inductions of white spot with γ-rays are photoreactivable in varying degrees, depending upon the strains of silkworm, to the extent of 10 to 50%.
2. Frequencies of white spots induced by γ-irradiation at 24 hrs after the second ecdysis have been influenced to a great extent by the differences of temperature after irradiation, resulting in higher frequency at high temperature (25°C or more) during the third and fourth instars, and in lower frequency at low temperature (16°C) during the third or the fourth instar.
3. The effects of implantation of brain, suboesophageal ganglion, corpus allatum or prothoracic gland on the frequencies of γ-ray induced white spots were investigated. The endocrine organs were transplanted into striped F₁larvae immediatly after the second ecdysis, then these larvae were irradiated at 24 hours after transplantation. Though the transplantation of brain, suboesophageal ganglion or corpus allatum did not show any significant effects, the larvae transplanted with prothoracic gland exhibited the decrease in their frequency of white spots up to 54% of control.