杠柳新苷P和E对东方粘虫和小地老虎幼虫中肠蛋白酶活性的影响

Effects of periplocosides P and E from Periploca sepium on the proteinase activities in the midgut of larvae of Mythimna separata and Agrotis ypsilon(Lepidoptera:Noctuidae)

从杀虫植物杠柳Periploca sepium Bunge根皮中分离得到的杠柳新苷P具有很高的杀虫活性,为了探索其杀虫机理,采用经典的昆虫蛋白酶活性测定方法,比较研究了杠柳新苷P和无杀虫活性的杠柳新苷E对东方粘虫Mythimna separata与小地老虎Agrotis ypsilon6龄幼虫中肠类胰蛋白酶和类胰凝乳蛋白酶活性的影响。结果表明:对东方粘虫弱碱性类胰蛋白酶,杠柳新苷P表现出强激活作用(酶活性为对照的3.43倍),激活时间可长达8h,而杠柳新苷E则无明显激活作用。杠柳新苷P和E对东方粘虫弱碱性类胰蛋白酶活性的影响二者差异显著(P=0.01),杠柳新苷P药后2,4和8h,东方粘虫中肠弱碱性类胰蛋白酶的活性分别是杠柳新苷E药后的15.4,106.8和242.7倍。酶活性测定结果还表明,与东方粘虫相比,小地老虎中肠类胰蛋白酶活性相对较低,且杠柳新苷P的激活作用也较弱,这可能是杠柳新苷P对东方粘虫具杀虫活性,而小地老虎对其不敏感的原因之一;另外,杠柳新苷P和E对试虫中肠类凝乳胰蛋白酶活性均无明显影响。据此推测,杠柳活性成分新苷P对东方粘虫中肠弱碱性类胰蛋白酶的激活作用可能是造成试虫中毒的机理之一。

Periplocoside P,which was isolated from the root bark of the insecticidal plant Periploca sepium Bunge,has strong insecticidal activity.To explore the insecticidal mechanism of periplocoside P,the classical determination methods for insect protease activity were used to compare the different effects on the activities of trypsin-like protease and chymotrypsin-like protease in the midgut of the 6th instar larvae of Mythimna separata and Agrotis ypsilon beween periplocoside P and periplocoside E which has no insecticidal activity.The results showed that periplocoside P displayed strong activation effect on the weakly alkaline trypsin-like protease activity in the midgut of M.separata larvae,which was 3.43 times as high as the control,and the activation time last up to 8 h;while periplocoside E did not show any activation effect.Significant differences at the 0.01 level between the effects of periplocosides P and E on the weakly alkaline trypsin-like protease activity of M.separata larvae were observed.At 2 h,4 h and 8 h after treatment,the weakly alkaline trypsin-like protease activity in the midgut of M.separata larvae treated by periplocoside P were 15.4,106.8 and 242.7 times as high as that in the midgut of M.separata larvae treated by periplocoside E.The results of protease activity determination also showed that the trypsin-like protease activity in the midgut of A.ypsilon larvae was relatively low,and the activation effect of periplocoside P on trypsin-like protease was also weak,compared to that on M.separata,which may be one of the factors that periplocoside P had insecticidal activity against M.separata,while A.ypsilon was insensitive to it.In addition,periplocosides P and E showed no obvious effect on chymotrypsin-like protease activity in the midgut of the tested insects.It is so inferred that the activation of the weakly alkaline trypsin-like protease in the midgut of M.separata may be one of the factors that periplocoside P causes toxicity to insects.