Chilling Injury in the Housefly: Evidence for the Role of Oxidative Stress between Pupariation and Emergence

Abstract

The hypothesis that oxidative stress plays a role in chilling injury in the housefly was investigated by determining the effect of chilling on two important components of the insect's antioxidant defense system: (i) the superoxide anion scavenging enzyme, superoxide dismutase, and (ii) the tripeptide, glutathione, which is significant in maintaining the cellular redox status of the cell. The observations that led to this hypothesis are: (i) the housefly exhibited an U-shaped curve in O2consumption rate during development at 28°C from pupariation to the pharate adult stage when sampled at 24-h intervals and (ii) O2consumption rates of these different age groups prior to chilling was negatively correlated to the time after acute transfer to 7°C required to observe a 50% reduction in adult emergence (LT50s) after their return to 28°C. Superoxide dismutase (SOD) activity changed during this period of development at 28°C in an inverted U-shaped manner and was positively correlated to their LT50s when acutely transferred and stored at 7°C. The SOD activity increased in the 12–24 h and 36–48 h postpupariation age groups at 7 and 10°C compared to the activity prior to chilling (Day 0). The 60–72 h postpupariation group and older showed initial reductions in SOD activity during cold storage when compared to Day 0. Total glutathione (GSH and GSSG) in the different age groups was typically decreased by cold storage. The percentage loss of glutathione in the different age groups after 7 days at 7°C was negatively correlated to their LT50s at 7°C. The significance of these changes in SOD activity and glutathione levels to chilling injury in the housefly is discussed.