Effects Of Heat Shock On Antioxidant Enzymes In The Fifth Instar Larvae Of The Silkworm, Bombyx Mori

Since the silkworm is poikiothermic, temperature plays a major role in growth and productivity of silkworm, Bombyx mori. In order to explore the biochemical and molecular mechanisms of Bombyx mori underlying resistance to heat shock, changes of antioxidant enzyme activity and the transcription levels of the related genes in the tissues of the 5th instar larvae of Bombyx mori were detected after heat shock with the methods of spectrophotometry and real-time fluorescent quantitative PCR. The main results have been reported as follows:1. Effects of heat shock on mortality rates and antioxidant enzymes in the silk gland, midgut and fat body tissues of the 5th instar larvae were compared between 7532 and Dazao, two bivoltine strains of Bombyx mori. The results indicated that the changes of antioxidant enzyme activity in the tissues of 7532 were related to its stronger resistance against heat shock than Dazao, the changes of antioxidant enzyme activity in the tissues of the 5th instar larvae showed significantly differences between different strains, in changes of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), we found that changes of GST activity could better reflect the ability to resist heat shock, and it would be one physiological and biochemical indicator in breeding of high-temperature-resistant species of Bombyx mori.2. The content of reduced glutathione and the changes of glutathione-related enzymes activity in the fat body tissue of the 5th instar larvae of Bombyx mori were assayed after heat shock. The results indicated that the content of glutathione in the fat body tissue of the 5th instar larvae of Bombyx mori decreased after heat shock, and the activity of GST and thioredoxin peroxidase (TPx) increased as the temperature increased, while no significant change was found in glutathione reductase (GR) activity. Overall, heat shock induced an increase in activity of antioxidant enzymes in Bombyx mori, and the ability of antioxidant defense system in Bombyx mori was enhanced. Heat shock didn't enhance the antioxidant capacity of GR, probably because thioredoxin reductase (TrxR) plays a leading role in resisting to heat shock in Bombyx mori.3. We have determined the transcription levels of BmPrx and BmTPx induced by heat shock in the fat body tissue of the 5th instar larvae of Bombyx mori. The results indicated that the transcription levels of BmPrx and BmTPx in the fat body tissue of the 5th instar larvae in Bombyx mori were induced by heat shock, and their variation regularities were consistent with the enzyme activity. The transcription levels of BmPrx were significantly higher than BmTPx before and after heat shock.This study explored the role of antioxidant enzymes against heat shock in Bombyx mori, and it can provide references for culturing new species of high-temperature-resistant silkworms.