Abstract: For better understanding the mechanism of inhibition action of bionic signal molecule(BSM)to the alkaloid accumulation in tobacco after topping,the changes of jasmonic acid(JA)content,and the activities of lipoxygenase(LOX)and ornithine decarboxylase(ODC)in tobacco plants under different treatments,including topping,topping followed by BSM application,and the control,were analyzed. The results showed that:1)JA content increased in tobacco leaves and roots after topping,while BSM application would inhibit the increasing rate of JA in roots and leaves,particularly in roots,which was reduced by 38.5% in 6 hours after application. 2) LOX activity in tobacco leaves obviously increased within 24 hours after topping. BSM application decreased LOX activity,it decreased the activity peak by 25.0%. 3)ODC activity in roots increased rapidly after topping. BSM application inhibited ODC activity,it reduced the activity peak by 11.2%. 4)By inhibiting LOX activity at the upstream of the wound signal path,then inhibiting JA content and ODC activity,BSM lowered alkaloid accumulation in tobacco after topping.