Effects of six plant secondary metabolites on activities of detoxification enzymes in Spodoptera litura
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abstract
Herbivorous insects encounter chemical defense in the form of numerous secondary metabolites in host plants. Understanding insect counter-defense mechanisms is important. In this study fifth instar Spodoptera litura insects were exposed to diets containing 0. 01% cinnamic acid, 0. 01% salicylic acid, 0. 01% xanthotoxin, 0. 02% quercetin, 0. 05% flavone and 0. 1% coumarin for 48 h. Activities of detoxification enzymes including glutathione S-transferase (GSTs), caboxylesterase (CarE), cytochrome P450 (P450) and acetylcholinesterase (AChE) were then determined in midguts and fatbodies, and transcript levels of CYP4M14 and CYP4S9 were examined by semi-quantitative RT-PCR. CarE activity in midguts was increased 1. 67-and 1. 37-fold after consumption of cinnamic acids and coumarin, respectively. All six plant secondary metabolites induced GSTs activity in the fatbodies. Total P450 activity in the fatbodies was increased 2. 93-and 14. 50-fold after consumption of cinnamic acid and coumarin, respectively. Consumption of cinnamic acid, xanthotoxin, quercetin and coumarin increased AChE activity 1. 53-, 1. 80-, 2. 36-and 1. 56-fold, respectively. All six plant secondary metabolites induced transcripts of CYP4M14 in the fatbodies of S. litura. Cinnamic acid, quercetin and coumarin strongly induced transcripts of CYP4S9 in the fatbodies. These results indicated that S. litura is able to induce its detoxification enzymes to minimize toxicity from plant secondary metabolites.
