Effects of Fraxinellone on the midgut enzyme activities of the 5th Instar Larvae of Oriental Armyworm, Mythimna separata walker

Abstract

Isolated from Dictamnus dasycarpus Turcz., fraxinellone exhibited multiple bioactivities against insects. In the present paper, the changes of digestive enzymes and detoxification enzymes of Mythimna separata Walker (5th instar larvae), treated with fraxinellone, were investigated. Compared with those of the control, the α-amylase activity of the fraxinellone-treated 5th instar larvae was inhibited, whereas the level of their protease activity was increased. Based upon further studies on the specific proteases, the levels of the active alkaline trypsin-like enzyme (BApNA as the substrate) and the chymotrypsin-like enzyme (BTEE as the substrate) activities of the treated larvae were declined; however, the level of activity of the weak alkaline trypsin-like enzyme (TAME as the substrate) of the treated ones was increased. Meanwhile, the activities of two detoxification enzymes, such as carboxylesterase (CarE) and glutathione S-transferase (GST), of the treated larvae were increased to some extent, but the activities of NADPH-P450 reductase and O-demethylase of the treated ones declined. Therefore, protease (especially the weak alkaline trypsin-like enzyme), CarE and GST played important roles in the metabolism of fraxinellone in the midgut of Mythimna separata (M. separata).

Figure 1

The chemical structure of fraxinellone.

Figure 2

Effects of fraxinellone on the activities of digestive enzymes. The uppercase letters of (A), (B) and (C) were represented the activities of lipase, α-amylase and non-specificprotease, respectively. Data in the figure are mean ± SE. Different lowercase letters indicate the significant differences among different groups (p < 0.05). The meanings of letter are the same in the following figures.

Figure 3

Effects of fraxinellone on the activities of specific proteases. The uppercase letters of (A), (B) and (C) were represented the activities of active alkaline trypsin-like enzyme, weak alkaline trypsin-like enzyme and chymotrypsin-like enzyme, respectively.

Figure 4

Effects of fraxinellone onthe activities of detoxification enzymes. The uppercase letters of (A), (B), (C) and (D) were represented the activities of CarE, GST, NADPH-P450 reductase, and P450 O-demethylase, respectively.