Diapause development and acclimation regulating enzymes associated with glycerol synthesis in the Shonai ecotype of the rice stem borer larva, Chilo suppressalis walker

Abstract

Overwintering larvae of the Shonai ecotype of the rice stem borer, Chilo suppressalis, enter diapause in early September and terminate diapause at the end of October. Cold acclimation at 0°C did not influence glycerol, trehalose or glycogen content in larvae collected on 22 September. Acclimation at 0°C increased the glycerol content and reduced the glycogen content significantly in larvae collected on 2 October and 22 November compared with acclimation at 15°C. These results indicate that overwintering larvae at different phases of diapause development respond differently to the low temperature stimulus for glycerol synthesis. Thus, we evaluated the metabolic rearrangements associated with glycerol synthesis during diapause development and after temperature acclimation. Larvae collected on 2 October were acclimated at 15°C for 15 and 60 days. Some of those acclimated at 15°C were then moved to 0°C for 15 days. The larvae acclimated at 15°C for 15 days were in deep diapause and accumulated little glycerol, while larvae acclimated at 15°C for 60 days were nearly ready to emerge from diapause and accumulated glycerol at 155.5 μmol/g. When larvae acclimated to 15°C for 15 days were transferred to 0°C, glycerol accumulation was stimulated to the same extent (ca 140 μmol/g) as it was in larvae that were acclimated to 15°C for 60 days and then transferred to 0°C. These results indicate that low temperature has a cumulative effect on glycerol production in larvae at different phases of diapause development. Glycerol accumulation was accomplished by activation of glycogen phosphorylase and inhibition of fructose-1,6-bisphosphatase, and activation of enzymes associated with glycerol synthesis, mainly glyceraldehyde-3-phosphatase and polyol dehydrogenase with glyceraldehyde activity.