苏云金杆菌预处理对棉铃虫乙酰胆碱酯酶的影响

THE EFFECT OF Bt PRETREATMENT ON ACETYLCHOLINESTERASE IN COTTON BOLL WORM

用苏云金杆菌(Bt)预处理24h后,棉铃虫幼虫体内乙酰胆碱酯酶对特异性酶抑制剂的亲和力发生了变化。在抗性品系中,幼虫的乙酰胆碱酯酶的酶动力学值和抑制中浓度均低于未处理对照幼虫,双分子速率常数则高于未处理对照幼虫,单位时间内抑制作用加快,差异显著,说明Bt预处理可能改变或激活了抗性幼虫乙酰胆碱酯酶的活化中心,因而增加了其幼虫乙酰胆碱酯酶与抑制剂的亲和力。由此推论,乙酰胆碱酯酶的改变是Bt预处理棉铃虫幼虫对杀虫剂敏感性提高的重要原因之一。Bt预处理和未处理敏感幼虫的双分子速率常数没有变化,但酶最大反应速度及抑制中浓度值升高,表明Bt预处理降低了敏感幼虫乙酰胆碱酯酶单位时间内的抑制作用,导致酶促反应速度加快,同时增加了对乙酰胆碱酯酶的半抑制剂量。

Acetylcholinesterase affinities in cotton bollworm Helicoverpa armigera (Hubner) larvae to the special inhibitors of the enzyme were changed after the larvae were pretreated with Bt for 24 h. In the resistant colonies, enzymatic kinetics (Km, Vmax) and half inhibition concentrations (I50)of the inhibitors to acetylcholinesterase activities in the larvae with Bt pretreatment were lower than those without Bt treatment, while the higher values of the bimolecular rate constant (ki)were detected in the larvae with Bt pretreatment. The inhibition of acetylcholinesterase was increased in a time unit, and there were significant differences between treated and untreated larvae, the results suggested that the active center of acetylcholinesterase might be changed or activated after Bt pretreatment, and the affinity of this enzyme to the inhibitors was increased. Consequently, the change of acetylcholinesterase is one of the important factors for increasing the sensitivity of the resistant larvae to insecticide. In the susceptible colony, although the difference between bimolecular rate constants (ki) of acetylcholinesterase in the larvae treated with and without Bt were not significantly different, higher values of Vmax and I50 were occurred in the larvae treated with Bt, suggested that the Bt pretreatment has reduced the inhibition of the special inhibitors to acetylcholinesterase in the susceptible larvae in the time unit, causing the accelerated enzymatic relation velocity and increased half inhibition concentration of the inhibitors.