| Aphids are major insect pests of global agriculture, damaging crops by direct feeding damage and by vectoring numerous devastating phyto-viruses. Aphids are the group piercing and sucking insect pests, the largest group of insect phloem feeders. During feeding, aphid salivary stylets penetrate plant tissues to feed on photo assimilates translocating in the phloem sieve elements. The prolonged interactions of aphid stylets with plant cell result in plant defense responses to aphids. Aphid probing may be influenced by changes in the chemical contents of the sieve element sap or physiological changes induced by aphid saliva. Watery digestive saliva is a more complex mixture of enzymes and other components capable of eliciting plant defense signals. To study the components and activities of enzymes of wheat aphids'watery saliva, and the capability of eliciting wheat defense signals, the results will be very to unveil the defense resistant mechanism of wheat induced by wheat watery saliva.In this paper, we used two kinds of wheat aphids, Sitobion avenae and Schizaphis graminum, and chosed aphid-wheat as an interaction system to detect the conponents and activities of enzymes in wheat watery saliva, and the wheat transcripts of key defence genes (genes for farnesy pyrophosphate synthetase, allene oxide sythase, phenylalanine ammonia-lyase) in different treatments of enzymes at biochemical and molecular levels, respectively. It was found the difference of conponents and activies of enzymes between two aphids'saliva, and the defense response and signalling transduction pathways in wheat elicited by different enzymes. The major results were as follows:S. avenae and S. graminum from the cultured room on wheat seedling in labortory, the components and the activities of enzymes of aphids'saliva were investigated and detected by the biochemical techniques. The results showed that polyphenol oxidase, pectinmethylesterase, cellulose were detected in S. avenae saliva, and the activities of 30 aphids were 6.2×10-3U/g, 3.26×10-3U/g, 6.86×10-3U/g. And polyphenol oxidase, multi-polygalacturonase enzyme, glucosidase were detected in S graminum saliva, the activities of 30 aphids were 2.37×10-1U/g, 1.16×10-2U/g, 1.24×10-3U/g. Because the oxidase can cause oxidate reaction in plant cell, compared with S. avenae, high polyphenol oxidase in S. graminum saliva may be the reason that the appearance of yellow spots symptom of on the infested wheat leaves by S. graminum .The capabilities of eliciting wheat defense signals by the two aphids'saliva and enzymes in saliva were studed through screening the gene transcription of key enzymes of wheat defense signal pathways by real-time fluorescence quantitative PCR technique. The results showed that polyphenol oxidase could induce the key enzyme genes expression of the wheat jasmonic acid (JA) signalling pathway, but had little effect in the salicylic acid (SA) signalling pathway. Pectinase could induce the key enzyme genes expression of the wheat JA and SA signal transduction pathway, but had little effect in the terpenoid signalling pathway. The cellulase could induce the wheat JA signalling pathway, but it seems could inhibit SA and terpenoid signalling pathway. The glucosidase could induce wheat JA, SA and terpenoid signalling pathway.The elicitors for saliva enzymes could deduced from the induced genes relative expression of key enzymes of defferent defense pathways in wheat. Because the relative expression of aos and fps increased to a different extent in wheat by treated with polyphenol oxidase, polyphenol oxidase was the elicitor of JA and terpenoid signal transduction pathway. The relative expression of aos and pal could significant increased by treated with pectinase, pectinase was the elicitor of JA and SA signal transduction pathway. The relative expression of aos increased by treated with cellulase, cellulase was the elicitor of JA signal transduction pathway. The relative expression of aos, pal and fps could significant increased by treated with glucosidase, glucosidase was the elicitor of JA, SA and terpenoid signal transduction pathway.
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