| Based on previous research works in a model system consisting of rice, the rice brown planthopper Nilaparvata lugens (Stal) and its egg parasitoid Anagrus nilaparvatae Pang et Wang, the volatiles-eliciting chemicals in the saliva of N. lugens and the roles of JA-, SA- and H2O2 signaling pathways in the release of N. lugens-'mdnced rice volatiles were studied. The results are as follows:1) H2O2 concentrations in rice plants were increased 0.5-24 h after attack by N. lugens, and reached its maximum at lh and 12 h. However, the production of H2O2 only occurred locally, rather than spreading over neighboring tissues. N. lugens attack also resulted in SA levels increases, which were always higher than those in the control during 1.5-24h after the start of the damage and reached its maximum at 4h. However, JA concentrations were not altered 0-24h after the herbivore damage.2) The parasitoid was obviously attracted by the volatiles emitted from rice plants that were wounded and treated with 50-250ug plant-1 H2O2 orl3.8-82.6p.g plant-1 SA. Collections and identifications of the volatiles released from the headspace of the plants demonstrated that H2O2 and SA applications to wounded plants increased the release of 12 and 13 chemicals respectively, and both of them enhanced the total volatiles. Moreover, all chemicals that were elicited by H2O2 or SA showed dose dependent increases. There were similarities and differences in volatiles profiling between N. lugens damaged paints and H2O2- or SA-elicited plants.3) The parasitoid showed no preferences for volatiles released from plants that were woundedand treated with SA, JA or H2O2. All 6 treatments of two signals applications to wounded plants (SA+JA, SA+H2O2, H2O2+JA, H2O2+SA, JA+SA, JA+H2O2) except JA+SA showed significant attractions to the parasitoid compared to the control, and presented similar activities as N. lugens damaged plants did. Among the six treatments of three signals applications (SA+JA+H2O2 SA+H2O2+JA H2O2+SA+JA H2O2+JA+SA JA+H2O2+SA, JA+SA+H2O2), the parasitoid only oriented to the volatiles emitted from SA+JA+H2O2 and H2O2+JA+SA treatments, whose attractiveness to the parasitoid were similar to N. lugens damaged plants. In rice plants, exogenous applications of JA or SA increased H2O2 concentrations, while H2O2 elicitation resulted in JA decreases and SA increases, suggesting a complex crosstalk among the three signaling pathways.4) Active chemicals present in the rice brown planthopper Nilaparvata lugens heads extraction that induced rice plants to release volatiles attractive to Anagrus nilaparvatae, an egg parasitoid of N. lugens, and they mainly belong to proteins. The activity in the extraction was lost when stored at -15-20℃ for 72 days, but it was kept for at least 5 weeks. Among volatiles emitted from rice plants that were wounded and treated with either a-glucosidase, P-glucosidase, a-amylase, or p-amylase, which are four main enzymes present in the saliva of N. lugens, only did volatiles emitted from p-glucosidase-treated plants attract the parasitoid. The parasitoid showed no preferences for volatiles released from N. lugens damaged plants compared to those from plants that were wounded and treated with either N. lugens heads extraction, proteins isolated from the extraction or P-glucosidase. Compared to the controls, the release of the volatiles was increased after rice plants were elicited with either N. lugens damage, N. lugens heads extraction, proteins isolated from the extraction or P-glucosidase, and all these treatments showed similar volatiles profiling. These suggest an important role of proteins, especially P-glucosidase in the saliva of N. lugens in the production of N. lugens-induced rice volatiles.5) Volatiles emitted from rice plants, 12h after the plants were wounding and treated with 0.01-0.04 unit plant-1 B-glucosidase in the NaOH-citric acid buffer (pH=6) showed a significant attractiveness to the parasitoid compared to the control (volatiles from plants thatwere wounded and treated wit... |
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