Formation of silk proteins by the silkworm, Bombyx mori, after gamma-ray irradiation in the embryonic stage

Abstract

Silkworm eggs were irradiated with gamma rays from 60Co for 50 hr, producing a total dosage of 8000 rad, in a late stage of embryonic development, and several biological and biochemical parameters have been measured with a view to gaining evidence on metabolic disturbances caused by the irradiation which particularly affect silk formation. After irradiation, there was no difference in hatchability of eggs, but mortality of larvae increased, the larval period was prolonged, and the rate of growth of the body and silk glands was reduced. In irradiated larvae, the posterior division of the silk gland was slightly reduced in cell number but the middle division was not. Increase in weight of the posterior division of the silk gland almost ceased after the middle of the fifth instar in irradiated larvae. The rate of formation of silk proteins was less throughout the whole period from the third to the eleventh day of the fifth instar in the irradiated larva. The formation of fibroin was conspicuously affected. Synthesis of silk proteins, especially fibroin, was much reduced in the treated larva during the spinning period. Fibroin-synthesizing activity and the content of nucleic acids in the posterior division of the silk glands of irradiated larvae were less than in the controls. Cell-free incorporation of 14C-glycine into protein in a system consisting of ribosomes and messenger RNA obtained from the posterior division of the silk glands indicated that irradiated larvae had lower activity of messenger RNA and accelerated activity of ribosomes.