Biochemical and molecular characterizations of Sitobion avenae-induced wheat defense responses

In this experiment, the aphid–wheat interaction system was chosen to study the changes in activity levels of key enzymes [lipoxygenase (LOX), polyphenoloxidase (PPO), phenylalanine ammonialyse (PAL) and β-1,3-glucanase] and in transcript level of key defense genes [encoding farnesyl pyrophosphate synthetase (fps), encoding allene oxide synthase (aos), and encoding phenylalanine ammonialyse (pal)] under pressure of aphid-feeding, aphid-induced volatiles, as well as specific volatiles using enzymes assay, RT-PCR and real-time quantitative PCR techniques. At the same time, the induction of enzymatic and transcript levels of defense genes with artificial wounding, wounding-induced volatiles and inductive chemical agents (jasmonic acid and methyl salicylate) were also studied. Our results showed that the activities of key enzymes which belong to both jasmonic acid (JA) and salicylic acid (SA)-signaling pathways increased significantly with aphid-feeding. The relative transcript levels of key defense genes in the signaling pathways were also enhanced. So we propose that aphid-feeding could activate both jasmonic acid (JA) and salicylic acid (SA)-signaling transduction pathways. Mechanical wounding and aphid-feeding are not equivalent. Sitobion avenae-induced volatiles elicit the transcript of all three defense genes in neighboring plants, suggesting that the volatiles emitted from aphid-infested plants might induce the activity of LOX followed by activating the JA-signaling pathway and the transcript level of multiple defense genes that JA mediates. 6-Methyl-5-hepten-2-one, 2-tridecanone and (E)-2-hexen-1-ol in S. avenae-induced volatiles not only activated the transcript level of defense genes, but also inhibited aphid-feeding behavior and population growth.