The involvement of reactive oxygen species in defense of wheat lines with the genes introgressed from <Emphasis Type="Italic">Agropyron</Emphasis> species contributing the resistance against brown rust

The role of reactive oxygen species (ROS) in the defense of nearly isogenic lines of common wheat (Triticum aestivum L., cv. Thatcher) with the genes of resistance to brown rust introgressed from Agropyron species was studied using light microscopy. This disease is induced by the fungus Puccinia triticina Erikss. The presence of superoxide anion in the sites of infection was detected with the dye nitro blue tetrazolium. In addition, we studied fungus development on plants treated with the inhibitor of Ca²⁺-channels, verapamil, disturbing penetration into the cells of Ca²⁺ required for ROS generation. During fungus development in the immune line with the Lr38 resistance gene (from A. intermedium (Host) Beuv.), oxidative burst developed at the sites of contacts of appressoria with stomata and exerted a fungicidic effect. When ROS generation was suppressed, the fungus developed haustoria in the mesophyll cells. In plants with the Lr19 gene (from A. elongatum (Host) Beuv.), only moderate amount of superoxide anion accumulated on the cell walls of stomatal guard cells and in the infection structures when the fungus penetrated into the substomatal cavity and in mesophyll cells. In plants with the Lr24 gene (from A. elongatum), superoxide anion was detected only around haustoria. Suppression of ROS generation in plants harboring the Lr19 and Lr24 genes did not affect fungus entrance into the substomatal cavity but facilitated penetration of haustoria into the mesophyll cells. At the same time, in the lines with the Lr1 gene (from T. aestivum), cytological examination did not detect O ₂ ^? accumulation in plant cells, whereas treatment with verapamil enhanced mycelium development. In all lines, the suppression of oxidative burst slowed the development of hypersensitive response.