Wu Haihua

Study on Insecticidal Activities and Effect on Three Kinds of Enzymes by 5-Aminolevulinic Acid on Oxya chinensis

Insecticidal activities and effects on three enzymic activities caused by 5-aminolevulinic acid (ALA) on Oxya chinensiswere studied. Fourth-instar nymphs of O. chinensis were treated with different doses of ALA (A1, 250 mM; A2, 450 mM; A3, 750 mM; A4, 1000 mM). Mortality and the activities of acetylcholinesterase (AChE), glutathione S-transferase (GSTs), and glutathione peroxidase (GPx) were determinated. The mortality of O. chinensis rose with an increasing dose of ALA. The mortality of high-dose treatments A3 and A4 reached 66.19 and 80.21%, respectively. The value of LD50 was 3.61 (3.29-3.93) mg g-l body weight (95% confidence interval). Biochemical studies showed that the activities of AChE and OPx in the A4 treatment declined by 51.53 and 42.82% in the female, and 42.65 and 43.85% in the male compared to the control, respectively, and the degree of decline reached a significant level at P＜0.05. Meanwhile, the OSTs activities of O. chinensis enhanced with increasing dose of ALA. The OSTs activities of female and male O. chinensis in the A4 treatment remarkably increased by 171.05 and 97.42% compared to the control (P＜0.05). ALA had an obviously toxic effect on O. chinensis. Moreover, ALA caused the photoinactivation of AChE and OPx, which induced nerve transmission blocking and the capability to defend oxidation damage declining. Meanwhile, a high dose of ALA could activate OSTs, which caused a feedback inhibition of the insect to the phototoxic substance.

Comparative Studies of Substrate and Inhibitor Specificity of Glutathione S-Transferases in Six Tissues of Oxya chinensis （Thunberg） （Orthoptera： Acrididae）

Specific activity, substrate specificity, and kinetic parameters (Km and Vmax) of glutathione S-transferases (GSTs) towards three substrates, 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), and p-nitrobenzene chloride (pNBC) were investigated in six tissues (foregut, midgut, hindgut, fat body, hemolymph, and muscle) of Oxya chinensis. In addition, the inhibition in vitro (ethacrynic acid, and Cibacron Blue 3GA) of Oxya chinensis in the six tissues was also investigated. Glutathione S-transferase activity was detected in all the six tissues examined. The rank order of GST activities towards CDNB was fat body > midgut > hindgut > muscle > foregut > hemolymph both in females and males. Glutathione S-transferase activities in the fat body in females and males were 1.3- to 10.4-fold and 1.1- to 10.0-fold higher than those in the other tissues. The rank order of GST activities towards the other substrates changed slightly. From these results, it was inferred that GSTs in the fat body and midgut played important roles in detoxifying xenobiotics including insecticides and plant allelochemicals in O. chinensis. In the three substrates examined, CDNB seemed to be the best substrate, followed by pNBC and DCNB. The kinetic parameters of GSTs were different among the six tissues. This suggested that GSTs in different tissues have various affinities and catalytic efficiency to substrates. In vitro inhibition study showed that the median inhibition concentration (IC50) values of the two inhibitois to GSTs from the six tissues were different. The results suggested that the two inhibitors have different inhibition potency to GSTs from the different tissues. The observed changes in kinetic parameters and inhibition in vitro among the six tissues of the insect might suggest that the number and structure of isoenzymes and their rate of expression varied for the different tissues.