Changes In Glutathione Redox Cycle Of The Bivoltine In Eggs Of Silkworm (Bombyx Mori) At The Different Phases Of Diapause

Recent work has demonstrated that hydrogen peroxide (H₂O₂) functions as a signaling molecule controlling different essential processes in plants and mammals. Glutathione redox cycle is including two types of reaction: (1) the oxidation of reduced glutathione (GSH) by H₂O₂ to oixized glutathione (GSSG) which is catalyzed by glutathione peroxidase (GPX), glutathione S-transferase (GST) and thioredoxin pero -xidase (TPX) and (2) the reduction of GSSG by NADPH to GSH which is catalyzed by glutathione reductase (GR) and thioredoxin reductase (TrxR).For the bivoltine strain of the silkworm, Bombyx mori, diapause processcan be devided initiation, maintenance and termination phase. Progeny diapause and nondiapause are indcuced by the incubations of 20 oC under continuous light and darkness during maternal embryogenesis. Moreover, diapause status can be terminated by chilling of 5 oC. In previous studies, we reported that metabolism of H₂O₂ is closely related to the regulation of diapause in bivoltine silkworm. As glutathione redox cycle plays an important role in the removal of H₂O₂, we further examined changes in glutathione redox cycle of bivoltine silkworm at above five different phases of diapause process in the present study. The main results are reported as follow:Changes in glutatione redox cycle at Initiation phaseCompared to nondiapause eggs, diapause eggs had lower GSH, GSSG and total glutathione, higher GSH and GSSG ratios, lower TPX, higher GR, no signifant differences of GST, whereas GPX and TrxR activities could not be detected in both diapause and nondiapause eggs. The results showed that the shift of glutathione redox cycle to a more reductive state during diapause initiation phase is due to weaker oxidation of GSH catalyzed by TPX and stronger reduction of GSSG catalyzed by GR..Changes in glutathione redox cycle at Maintenance phaseDuring the maintenance phase, variations of glutathione and activities of TPX,GR and GST were not significant,whereas GPX and TrxR activities could not be detected. The results showed that, during diapause maintenance, the glutathione redox cycle maintains in reductive state..Changes in glutathione redox cycle at Termination phaseCompared to 25 oC, chilling of 5 oC resulted in lower GSH, higher GSSG and total glutathione, lower GSH and GSSG ratios, higher TPX and GST, lower GR in eggs. The results showed that the shift of glutathione redox cycle towards a more oxidative state during diapause termination phase is due to the stronger oxidation of GSH catalyzed by TPX and GST and the weaker reduction of GSSG catalyzed by GR.Besides,the variations of levels of BmTPX and BmPrx were in accordance with the variations of TPX activities at the different phases of diapause.Taken together, our results clearly showed that the glutathione redox cycle was in an oxidative state at diapause termination phases, whereas in a reductive state at diapause initiation and maintenance phase. Above changes in glutathione redox cycle suggested that glutathione may play an important role in the regulation of Bombyx diapause. The possible role and molecular mechanism of glutathione in diapause regulation of B. mori should be further elucidated.