Roles of peroxidases and NADPH oxidases in the oxidative response of wheat ( T riticum aestivum ) to brown rust ( P uccinia triticina ) infection

The goal of this work was to establish which enzymes – peroxidases or NADPH oxidases – play the most important role in the resistance‐related oxidative burst response of wheat to infection by brown rust ( P uccinia triticina ). The expression of four peroxidases and two NADPH oxidases was analysed in the susceptible wheat cv. Thatcher and isogenic lines with different Lr resistance genes after pathogen inoculation. Of the peroxidases, TaPrx118 and TaPrx112 were induced several times more strongly than TaPrx103 and TaPrx107 . The induction of peroxidases was more pronounced than that of NADPH oxidases. The patterns of peroxidase expression clearly differentiated moderately resistant from highly resistant lines and corresponded to oxidative response profiles. The possible involvement of peroxidases or NADPH oxidases was verified with enzyme‐specific inhibitors. The oxidative burst in the susceptible cv. Thatcher and in the lines Tc Lr24 , Tc Lr25 , Tc Lr9 was peroxidase‐dependent, while the response in line Tc Lr26 was NADPH ‐oxidase‐dependent. It is postulated that class III peroxidases play a leading role in the formation of reactive oxygen species molecules during the response of wheat to pathogen infection. The results suggest a high level of redundancy of some peroxidase genes induced in biotic stress. The role of both enzyme systems in wheat response/resistance to brown rust is discussed in relation to the oxidative response, the efficiency of resistance, and the presence and origin of particular Lr resistance genes.