Abstract: The degradation dynamics of Cry1Ac insecticidal protein in the leaves of Bt cotton while exposure to air and soil mediums under different conditions were investigated in both the laboratory and in the field. The results showed that the degradation trends under different situations were different. Bt insecticidal protein in cotton leaves degraded rapidly in first several days, then got slowly and entered a relative stable stage in which Cry1Ac protein content kept at a concentration about 50 ng·g-1. The higher temperature and lower humidity significantly increased degradation speed of the toxin, which shortened the period for the content of the protein to get into stable stage. However, there were no significant difference of the degradation under light or dark treatments. In natural environment, the insecticidal protein in Bt cotton degraded much rapidly in the initial period, it reached 85% in first month, and slowered during winter season, then degraded quickly in next spring until to be undetectable in late April.

Key words: Bt transgenic cotton, Bt insecticidal protein, Degradation dynamics