Metabolism Of Glutathione During Diapause Induction And Initiation In The Bivoltine Silkworm, Bombyx Mori

The silkworm, Bombyx mori, is a typical insect species which enters embryonic diapause. The bivoltine strain of Bombyx mori becomes the producers of diapause and non-diapause eggs when embryogenesis from stage 20 to stage 25 is incubated at 25℃under continuous illumination (LL) and 15℃under continuous darkness (DD). However, diapause initiation can be effectively prevented with the hydrochloric acid (HCl) treatment at 24 h post-oviposition.Our results obtained in previous studies suggest that the metabolism of hydrogen peroxide (H2O2) is closely related to diapause induction and initiation of the silkworm, Bombyx mori, in which H2O2 may play an important role in diapause induction and initiation. Glutathione (GSH) is the most abundant low molecular weight thiol compound synthesized in cells. GSH plays critical roles in protecting cells from oxidative damage and the toxicity of xenobiotics electrophiles, and maintaining redox homeostasis. The intracellular GSH level is a sensitive indicator for cellular stress. The ratio of GSH and GSSG contents could be signals to regulate cell processes include cell growth and death. Glutathione S-transferases are enzymes widespread in both prokaryotic and eukaryotic cells and catalyze the glutathione conjugation reaction with reduced glutathione to detoxification and antioxidation while reduced glutathione can be oxidized in these processes, and GST can restore the proteins damaged by active oxygen with reduced glutathione.In the present study, Levels of total glutathione, GSH, GSSG, GSH/GSSG and activities of Glutathione S-transferase (GST) in the bivoltine strain were determined with ultraviolet spectrophotometry to characterize special patterns of glutathione metabolism coinciding with the diapause induction and initiation of silkworm, Bombyx mori. The results showed that parameter mentioned above exhibited different profiles during different phase of diapause in the bivoltine strain. They can provide references for further study of diapause associated with glutathione metabolism. The results are as follows.1 Metabolism of glutathione during the diapause induction Compared to LD, eggs incubated at HI had significantly higher total glutathione, lower reduced glutathione (GSH), higher oxidized glutathione (GSSG), lower GSH/GSSG ratio and lower GST activity from stage 20 to stage 25 of embryogenesis, indicating that the pro-oxidant conditions at the diapause induction phase is mainly resulted from the stronger oxidation of GSH into GSSG.2 Metabolism of glutathione during the diapause initiation Compared to the eggs treated with hydrochloric acid, diapause eggs had significantly lower total glutathione, no significant difference of GSH, lower GSSG, higher GSH/GSSG ratio and no significant difference of GST activity from 24 h to 96 h after oviposition, indicating that the reduced conditions at the diapause initiation phase is mainly resulted from the weaker oxidation of GSH into GSSG.The total glutathione, reduced glutathione, oxidative glutathione rapid increased after on-time hydrochloric acid treatment, but no significant effect of the hydrochloric acid treatment on reduced glutathione and the activity of GST, indicated that the on-time hydrochloric acid treatment made the reduced status of embryogenesis reverse to pro-oxidative press.Our results obtained in this work suggested that variation of GSH/GSSG ratio in eggs of the bivoltine strain (B. mori) is in relation to diapause induction and initiation.(1) The pro-oxidant conditions coincided with the diapause induction, (2) The reduced conditions coinciding with diapause initiation, while the pro-oxidant conditions coinciding with the prevention of diapause initiation, and (3) the weaker oxidation of GSH in eggs of the bivoltine strain (Bombyx mori) catalyzed by peroxiredoxin (Prdx) rather than GST is in relation to diapause initiation.