The involvement of reactive oxygen species in the resistance response of wheat to the Russia wheat aphid
English: The effect of Russian wheat aphid (RWA), (Diuraphis noxia, Mordvilko), infestation on the activities of the reactive oxygen species (ROS) generating and scavenging enzymes as well as the hydrogen peroxide content were studied in resistant (cv., Tugela DN) and the near isogenie susceptible (cv., Tugela) wheat (Triticum aestivum L.) cultivars. Infestation resulted in an early induction (6-9h after infestation) of the activities of the ROS generating enzymes, NADPH oxidase and superoxide dismutase (SOD), in resistant plants only. These increased enzyme activities correlated with the increased H202 content in infested resistant plants. The activities of the ROS scavenging enzymes, glutathione reductase and ascorbate peroxidase were selectively induced somewhat later (12h after infestation) in resistant plants. Results suggest art early involvement of the ROS, and relevant ROS generating and scavenging enzymes in the resistance response of wheat to the RWA. Inhibitory studies were performed in vivo using diphenylene iodonium (DPI), an inhibitor of NADPH oxidase, to shed light on the possible upstream role ofROS in defence against the RWA in infested resistant plants. DPI substantially inhibited the RWA induced NADPH oxidase activity and the concomitant accumulation of H202. This resulted in the inhibition of activities of the secondary defence related enzymes, β-1,3-glucanase and peroxidase, suggesting a signaling role for H202 in RWA resistance through activation of defence genes. Accordingly, treatment of plants with the H202 generating mixture of glucose and glucose oxidase resulted in induction of the H202 production as well as induction of the β-1 ,3-glucanase and peroxidase activities in resistant plants. In vitro inhibition studies confirmed that DPI is a specific inhibitor of NADPH oxidase and did not have any direct inhibitory effect on the β-1 ,3-g1ucanase and peroxidase activities. This finding further substantiated that H202 generated during RWA infestation was involved in the signaling events leading to induction of the secondary defence responses in resistant plants.
Afrikaans: Die invloed van Russiese koringluis-(RKL), (Diuraphis noxia, Mordvilko) infestering op reaktiewe suurstofspesies (ROS)-produserende en -opruimende ensiemaktiwiteite asook waterstofperoksiedinhoud van weerstandbiedende (cv., Tugela DN) en die naisogeniese vatbare (cv., Tugela) koring-(Triticum aestivum L.) kultivars is ondersoek. Infestering het die vroeë induksie (6-9 ure na infestering) van die aktiwiteite van die ROS-produserende ensieme, NADPH-oksidase en superoksieddismutase (SOD) in weerstandbiedende plante tot gevolg gehad. Hierdie verhoogde ensiemaktiwiteite het met die verhoogde H202-inhoud in geïnfesteerde weerstandbiedende plante gekorrelleer. Die aktiwiteite van die ROS-opruimende ensieme, glutatioonreduktase en askorbaatperoksidase was ietwat later (12 ure na infestering) selektief in weerstandbiedende plante geïnduseer. Die resultate het op die vroeë betrokkenheid van ROS en relevante ROS-produserende en -opruimende ensieme in die weerstandsrespons van koring teen die RKL gedui. Remmingsstudies is in vivo met behulp van difenileenjodonium (DPI), 'n NADPHoksidaseremstof, uitgevoer om lig op die moontlike stroomoprol van ROS in verdediging teen die RKL in geïnfesteerde weerstandbiedende plante te werp. DPI het die RKL-geïnduseerde NADPH-oksidase-aktiwiteit en gepaardgaande H202- akkumulering aansienlik gerem. Dit het remming van die aktiwiteite van die sekondêre verdedigingsverwante ensieme, β-1,3-glukanase en peroksidase, tot gevolg gehad, wat op 'n seiningsrol vir H202 d.m.v. verdedigingsgeenaktivering gedui het. Dienooreenkomstig, het behandeling van plante met die H202-produserende mengsel, glukose-en glukose-oksidase, tot die induksie van β-1,3-glukanase en peroksidaseaktiwiteite in weerstandbiedende plante gelei. In vitro remmingsstudies het bevestig dat DPI 'n spesifieke remstof van NADPHoksidase is en dat dit geen direkte remmingsinvloed op β-1,3-glukanase en peroksidase-aktiwiteite gehad het nie. Hierdie bevinding het bykomstig bevestig dat H202, geproduseer tydens RKL-infestering, by die seiningsgebeure wat tot die induksie van sekondêre verdedigingsreaksies in weerstandbiedende plante lei, betrokke is.