Variations of hydrogen peroxide and catalase expression in Bombyx eggs during diapause initiation and termination

For diapause eggs of the silkworm, Bombyx mori , diapause initiation is prevented with hydrochloric acid (HCl) at around 20 h post‐oviposition while diapause status is terminated with chilling around 5°C. To investigate whether hydrogen peroxide (H 2 O 2 ) and catalase expression are involved in diapause initiation and termination, the concentration of H 2 O 2 , relatively higher levels of catalase mRNA and activity of catalase were compared between (1) 20‐h‐old diapause eggs and the HCl‐treated diapause eggs, and (2) 10‐day‐old diapause eggs and the 5°C‐chilled diapause eggs. Compared to diapause eggs, the HCl‐treated eggs had significantly higher H 2 O 2 concentrations (up from approximately 1–3  µ mol/g fresh mass to 5–8  µ mol/g fresh mass), higher relative level of catalase mRNA (up from 0 to 35.2%) and higher catalase activity (up from 2.51 units/mg protein to 4.97 units/mg protein) at 96 h post‐treatment. On the other hand, the 5°C chilling resulted in significant increases of H 2 O 2 concentration (up from 0.79  µ mol/g fresh mass to 5.57  µ mol/g fresh mass), relative level of catalase mRNA (up from 0 to 71.4%) and catalase activity (up from 0.88 units/mg protein to 3.42 units/mg protein) within 120 days. The results obtained in this work suggest that variations of H 2 O 2 and catalase expression in Bombyx eggs are involved in diapause initiation and termination. © 2011 Wiley Periodicals, Inc.