Ethylene signaling pathway plays an important role in induced plant direct defense against herbivores and pathogens; however, up to now, only few researches have focused on its role in induced plant indirect defense, i.e. the release of herbi- vore-induced volatiles, and the results are variable. Using a model system consisting of rice plants, the rice brown planthopper Nilaparvata lugens and its egg parasitoid Anagrus nilaparvatae, we examined the role of ethylene signaling in the production of rice volatiles induced by N. lugens by measuring both the timing of herbivore-induced ethylene levels and the relationships between ethylene, rice volatiles and attraction of the parasitoid. N. lugens infestation sig- nificantly enhanced the release of ethylene during 2―24 h after infestation. Plants treated with eth- ephon, a compound that breaks down to release ethylene at cytoplasmic pH, released volatiles profiles similar to those released by N. lugens-infested plants, and both of them showed an equal attraction of the parasitoid. Moreover, pretreatment with 1-MCP, an inhibitor of ethylene perception, reduced the release of most of rice volatiles whose amount was enhanced by N. lugens infestation and decreased the attrac- tiveness to the parasitoid. These results demonstrate that ethylene signaling is required for the production of rice volatiles induced by N. lugens.
β-Glucosidase has been reported to induce the production of herbivore-induced plant volatiles. How-ever, how it works remains unclear. Here, we investigated the levels of salicylic acid (SA), jasmonic acid (JA), ethylene, and H2O2, all of which are known signaling molecules that play important roles in in-duced plant defense in rice plants treated with β-glucosidase, and compared these to levels in plants infested by the rice brown planthopper Nilaparvata lugens (Stl). Results showed that wounding and treatment by β-glucosidase increased the levels of SA, ethylene, and H2O2, but not JA, in all plants compared to control plants. The signaling pathways activated by β-glucosidase treatment are similar to those activated by an infestation by N. lugens, although the magnitude and timing of the signals elicited by the two treatments are different. This may explain why both treatments have similar volatile profiles and are equally attractive to the parasitoid Anagrus nilaparvatae Pang et Wang.
WANG XiaZHOU GuoXinXIANG CaiYuDU MengHaoCHENG JiaAnLIU ShuShengLOU YongGen
