Involvement of lipoxygenase in resistance of wheat against the Russian wheat aphid

[摘要] English: The upstream role of lipoxygenase (linoleate: oxygen reductase, E.C. 1.13.11.12) inthe induced defence response against the Russian wheat aphid (Diuraphis noxia) wasstudied in resistant wheat (Triticum aestivum L.) cultivars Tugela-DN (Dn1), Tugela(Dn2) and Tugela (Dn5) and the near isogenie susceptible cultivar, Tugela.The RWA induced LOX was partially characterised. The pH for optimum LOXactivity was 5.6 and it had no requirement for cofactors such as K+, Mg2+ or Ca2-The enzyme also had a high affinity for linoleic acid, with a Km-value of -5.8 x10-4M.LOX activity was selectively induced in infested resistant Tugela cultivars containingthe (Dn1), (Dn2) and, to a lesser extent, (Dn5) resistant genes. The differentialinduction of LOX activity corresponded with the induction of the hypersensitiveresponse during the resistance response of Tugela-DN against the RWA. Theincorporated resistant gene affected the level of induced LOX activity, which roughlycorresponded with the cultivars' levels of resistance. Localised RW A infestation ledto a systemic increase in LOX activity. All indications were that the induced LOXactivity was involved in the resistance response in wheat against the RWA. Inhibitorystudies were performed with LOX inhibitors, piroxicam, salicylhydroxamic acid andn-propyl gallate, to shed light on the possible upstream role of LOX. Piroxicam wasthe most suitable inhibitor due to the fact that it only inhibited LOX activity in vitro.Inhibition of LOX activity in vivo by piroxicam, led to the inhibition of 'downstream'defence responses such as peroxidase and β-l ,3-glucanase activities. The selectiveincrease in LOX activity did not correlate with a selective increase in jasmonic acidconcentrations. The effect of intercellular injected JA on LOX, peroxidase and β-1 ,3-glucanase activities, indicated that jasmonic acid was not the primary product of theRWA induced LOX activity and that it was not the signal molecule in theRWA /wheat resistance response. The products of the RWA induced LOXs appearedto be derived from the 9-hydroperoxide derivative pathway, rather than the 13-hydroperoxide derivative (jasrnonic acid precursor) pathway. Neither was abscicicacid a product of the selective increased LOX activity, nor playing a role in the RWAresistance response in wheat. Other studies in our laboratory showed that salicylicacid is probably the signal molecule, activating defence genes after elicitation. It isevident that the RWA resistance response corresponded with that of pathogenesis, andthat each defence response follows its own distinctive defence cascade.

[发布机构] University of the Free State