Involvement of active oxygen species and phenylalanine ammonia-lyase in the resistance responsr of wheat to the Russian wheat aphid

[摘要] The effect of Russian wheat aphid (RW A), Diuraphis noxia (Mordvilko) infestationon phenylalanine ammonia-lyase (PAL) and superoxide dismutase (SOD) activities aswell as internal hydrogen peroxide (H202) levels and phenolic acid composition wasstudied in resistant (Tugela DNI) and susceptible (Tugela) wheat cultivars. In thisstudy we aimed to learn more about the resistance response of wheat against the RW Awith special reference to the role of active oxygen species (AOS), in particular H202,in establishing the down stream defense response and furthermore to investigate theinvolvement of phenylalanine ammonia-lyase (PAL) and phenolic compounds in theresistance response.SOD, PAL, POD (peroxidase) and chitinase activities were determined by means ofspectrophotometric essay procedures. The phenolic compounds were separated usingHPLC and a C-18 reverse phase column. Allopurinol was used to inhibit xanthineoxidase activity and concomitant H202 generation. The expression of the down streamdefense response was measured in terms of POD and chitinase activities.RWA infestation selectively induced H202 production to a maximum concentration 8h.p.i. in resistant wheat. The increase in H202 concentration corresponded with theincrease in SOD activity, which was also differentially induced in infested resistantwheat to a maximum value 8 h.p.i. These results suggest that SOD is involved in thegeneration of H202 during the hypersensitive reaction (HR). Inhibitory studies done,have proven that H202 was needed for the induction of the down stream defenseresponse. Chitinase activity was extremely low when the production of H202 wasinhibited by allopurinol.PAL activity increased differentially in infested resistant wheat to higher levels(200% increase) than in infested susceptible wheat. Peak activity of PAL was reachedbetween8-48 h.p.i. The increase in the activity of PAL, a key enzyme in thesynthesis of phenolic compounds, was reflected in increased phenolic acidconcentrations. Some of the phenolic acids that were selectively induced in resistantwheat upon RW A infestation were, p-hydroxybenzoic acid, gallie acid, resorcylicacid, gentisic acid, caffeic acid, p-hydroxyphenylacetic acid and ferulic acid. The P:hydroxybenzoic acid, p-hydroxyphenylacetic acid, caffeic acid and ferulic acidconcentrations corresponded to the peak PAL activity.Selective increases in PAL activity, caffeic and ferulic acid concentrations probablycontributed to the selective lignification of mesophyll cells in infested resistant wheat.This is a manifestation of the HR, which is part of the defense response against theRWA.Findings in this study were indicative of the involvement of active oxygen species inestablishing the down stream defense response and of phenolic compounds in theresistance response of wheat against the RWA.

[发布机构] University of the Free State