Effect of radiation on the embryonic midgut of the silkworm

In order to determine the effect of X-rays on embryonic midguts of the silkworm (Bombyx mori L.), embryos of C108 strain were X-irradiated (180 kVp, 25 mA, 1.0 mm Al filter and a dose-rate at 300 R/min) at different stages ranging from 44 to 128 hours after oviposition to the stage organogenesis. Histological observation was made on the midguts from treated or nontreated embryos which had grown up to the stage of abdominal pigmentation. The midgut of embryos younger than 80 hours was remarkably damaged following X-irradiations with Ld50 dose-range (1.5 KR). The midgut of embryos from 44 to 68 hours after oviposition or in the very early phase of organogenesis was most radiosensitive the midgut of embryos older than 92 hours was almost completed and X-irradiation caused slight damage. No significant histological damage was observed in the midgut of embryos older than 104 hours even after the treatment with a high dose of X-rays (4.0 or 6.0 KR). The sensitivity of the midgut to X-rays correlated with the embryonic lethality. Whether the midgut is a principal target of radiation was discussed. (author)