麻疯树佛波酯对菜青虫体内几种酶活力的影响

Effects of Phorbol Esters from Jatroph curcas on Several Kinds of Enzymes in Pieris rapae Larva

麻疯树佛波酯是麻疯树中最主要的毒性成分。文章研究了取食麻疯树佛波酯后,三龄菜青虫体内的超氧化物歧化酶(SOD)、中肠蛋白酶、Ca2+-ATP酶以及蛋白激酶C(PKC)活力的变化,旨在探讨麻疯树佛波酯对菜青虫的杀虫作用机理。结果表明:取食低浓度的佛波酯刺激菜青虫体内SOD活力增加,而超过16μg·mL-1的处理浓度则会使SOD活力显著下降。麻疯树佛波酯对试虫中肠蛋白酶活力有较强的抑制作用,8μg·mL-1的处理浓度下其比活力显著低于对照组(t测验,P<0.05),随着佛波酯浓度增加,其抑制作用也增大。此外,佛波酯对菜青虫神经细胞膜上Ca2+-ATPase的活性也具有明显的抑制作用。在一定的浓度范围内,菜青虫中肠细胞PKC活力随佛波酯处理浓度升高而升高,64μg·mL-1时PKC比活力最高,达到对照的2.35倍;同时胞膜PKC/胞浆PKC比值升高,伴随着明显的质膜转位。取食麻疯树佛波酯后3h,试虫中肠细胞PKC活力即显著高于对照(t测验,P<0.05),在12h活力达到最大值,为对照组的4.4倍。由于麻疯树佛波酯结构与PKC的激活物二酰基甘油(DAG)类似,因此能显著激活试虫体内的PKC,PKC可能是麻疯树佛波酯发挥杀虫作用的重要靶标。

Phorbol ester was a main toxin in Jatroph curcas seed. In order to investigate the insecticidal mechanism of phorbol esters against Pieris rapae larva, the enzyme activities of super-oxide dismutase （SOD）, midguts protease, Ca2＋-ATPase and protein kinase C （PKC） were examined in this paper. The results suggested that the activities of SOD were increased when exposure to low concentrations of phorbol esters. Interestingly, the activities would decrease when the concentrations of phorbol esters were higher than 16 μg·mL-1. Additionally, phorbol esters could significantly inhibit the activities of midguts protease in vitro and in vivo. Protease activities were significantly lower than the control even at 8 μg·mL-1 phorbol esters （t-test,P＆lt;0.05）, and the inhibition effect became more intense with the increasing of phorbol esters concentrations. Furthermore, phorbol esters could significantly inhibit the activities of Ca2＋-ATPase in P. rapae. On the contrary, activities of PKC in midgut cells were significantly enhanced when P. rapae were exposed to phorbol esters. The change of PKC activities was dose and time dependent and the highest PKC activities at a dose of 64 μg·mL-1 after exposure for 12 h. In addition, the increased ratios of membrane PKC to endochylema PKC could cause a translocation from endochylema to cell membrane. Our results indicated that PKC could be significantly activated by phorbol esters and was likely to be the molecular target of phorbol esters. The activation of PKC probably contributed to the insecticidal activities of phorbol esters against P. rapae larva.