The Effects Of Tutin And Its Derivatives On Protective Enzymes And Gaba Shunt Enzymes In Pseudaletia Separata

Tutin is a toxic compound of sesquiterpene with insecticidal action and antibacterial action. It was proved to inhibit the receptors of the neurotransmitterγ-aminobutyric acid (GABA) by the previous study. When tutin act on test larvae, the nerveconduction was blocked, and lesion came up on the malpighian tube and midgut, which finally led to the death of test larvae.In order to explore the insecticidal mechanism of tutin and its derivatives, this study synthesized used tutin and its four new acylation derivatives 2-(4-methoxybenzoyloxy)-tutin (T1), 2-(3,5-dinitrobenzoyloxy)-tutin (T2), 2-(6-chloronicotinoyloxy)-tutin (T3) and 2-(4-nitrobenzoyloxy)-tutin (T4) to determine their effects on antifeedant activity, protective enzyme system and the GABA shunt enzymes.In this work, we determine peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), glutamic acid decarboxylase (GAD) andγ-aminobutyric acid transaminase (GABA-T) activities of these compounds in 3rd instar larvae of P. separata. Clear antifeedant activities were manifested by T1 and especially T3, the highest antifeedant activity reached to 88%, whereas T4 stimulated the appetites of P. separata. It was observed that the effects of tutin and its benzoyl derivatives on the three protective enzymes had clear significant differences (P < 0.05). POD and CAT activities were inhibited by tutin and its benzoyl derivatives, but SOD activity was weekly promoted. This study indicated that tutin and its derivatives disturbed the detoxification process, consequently led to the accumulation of·O2- radical and H2O2 and finally hurt the physiological environment in the larvae of P. separata. GAD and GABA-T activities in larvae treated with all five toxins (Tutin, T1, T2, T3, and T4) differed significantly from the control and from one other (P < 0.05) in terms of treatment types and exposure times (the effects of the toxins on GAD and GABA-T were time-dependent for 48 h). GAD activities were inhibited by Tutin, T2, T3 and T4, and enhanced by T1; and GABA-T activities were increased by all the toxins in varying degrees. Variation of GABA content in P. Separata larvae resulted from the disturbance of GAD and GABA-T by tutinTutin and its derivatives.From the above study, T3, with its nicotinoyl group, was proved to be the most promising novel active ingredient for pest control. There were two methods of enzyme activity determination, one was feeding the larvae with toxins, and the other was adding toxins into enzyme directly. The enzyme activities determined by two methods were similar. This indicated that the method of activities determination of enzymes adding toxins directly could be used on the activities quick determination of new compounds. The determination of enzyme activity provide a basis for futher study about the relate enzyme gene target of tutin and its derivatives .