Abstract: Camptothecin possesses excellent inhibitive effects on insect growth and development. The apoptotic induction mode and mechanism of camptothecin are ambiguous, which restricts the application of camptothecin in plant protection. In order to investigate its inhibitive effect at the cellular level, the apoptotic induction effect of camptothecin on Spodoptera frugiperda Sf9 cells was studied. Induced with 1 μmol/L camptothecin, Sf9 cells showed typical morphological changes such as cell shrinkage, loss of microvilli and chromatin condensation under the transmission electron microscope. DNA Ladder assay indicated that camptothecin induced apoptosis in Sf9 cells. Apoptotic rate of Sf9 cells treated with 1 μmol/L camptothecin increased within 12 h, and reached the maximum of 39.67% at 12 h, which was 13.13 times as high as that of the control. In addition, the activity of Sf caspase-1, the homolog of mammalian effector caspase, increased after apoptosis induction in Sf9 cells, which reached the maximum at 12 h and 24 h, respectively. Furthermore, camptothecin inhibited Topo Ⅰof Sf9 cells to unwind supercoiled pBR322 DNA, which caused DNA damage to activate caspase. This suggests that the signal transduction pathway of caspase cascade is one of mechanisms of apoptosis induction. This study provides important clues to understanding the mechanisms of apoptosis induction.

Key words: Spodoptera frugiperda, camptothecin, Sf9 cells, apoptosis, cascade, flow cytometry