Eliciting and signal transduction events of the Russian wheat aphid resistance response in wheat

English: Features of the upstream defense response in the interaction between wheat (Triticum aestivum L.) and the Russian wheat aphid (RWA) (Diuraphis noxia, Mordvilko) were investigated. The study was conducted in an attempt to shed light on the eliciting and signal transduction events of the defense mechanism. It was found that the intercellular wash fluid (IWF) of infested resistant wheat plants (Tugela Dn 1), injected intercellularly into susceptible (Tugela) and resistant (Tugela Dn 1) plants had much higher eliciting activity than the IWF of infested susceptible plants. The eliciting activity was measured in terms of the expression of downstream defense related peroxidase and β-1,3-glucanase activities. The defense related enzymes were differentially induced to higher levels in the resistant than susceptible plants. Fractionation of the IWF of infested resistant plants by C-18 reverse-phase and con A binding chromatography revealed the elicitor to be a glycoprotein capable of inducing both local and systemic defense responses. The signaling role of salicylic acid (SA) in mediating the downstream defense responses was also investigated. RWA infestation induced differential accumulation of SA to higher levels in the resistant (421-fold) than susceptible (78-fold) plants. The increase in the activity of the defense related peroxidase in infested resistant plants correlated well with the increase in SA content. Intercellular application of H202 induced a 65% increase in SA content only in the resistant plants. As SA was accumulating, catalase activity was declining. In addition, intercellularly applied SA also inhibited catalase activity by 49%. The results from this study indicated that the intercellular glycoproteins from infested resistant plants can act as elicitors of the downstream defense responses and that SA is most probably a signaling molecule in mediating these responses.