Cytochemical localization of reactive oxygen species (O2− and H2O2) and peroxidase in the incompatible and compatible interaction of wheat – Puccinia striiformis f. sp. tritici

The subcellular localization of superoxide anion (O2−) and hydrogen peroxide (H2O2) and peroxidase activity has been studied in leaves of wheat plants cv. ‘Suwon 11’ infected with an incompatible pathotype CY23 and a compatible pathotype CY31, 5 days after inoculation (dai) using cytochemical methods. O2− and H2O2 were detected by means of Mn/DAB and CeCl3 staining methods; peroxidase was demonstrated using the DAB procedure. Distinct differences in intensity and distribution of O2− and H2O2 were found in both interactions. In general, precipitates of both reactive oxygen species (ROS) were more pronounced in the incompatible interaction compared to the compatible relation. In the incompatible interaction O2− and H2O2 were found in the cell wall, plasma membrane and tonoplast of mesophyll cells in contact with death cells of HR, and mesophyll cells adjacent to hyphae. In addition, H2O2 was detected in tonoplasts of host cells penetrated by haustoria, in the intercellular space and in walls of hyphae extending intercellularly. The subcellular accumulations of both ROS were restricted to the infection sites. However, in the compatible relation O2− was not detected in the host cell wall and plasmalemma and H2O2 was not found in tonoplasts of mesophyll cells as well as in tonoplasts around haustoria in infected host cells. Peroxidase was demonstrated in cell walls, intercellular spaces, plasma membrane of mesophyll cells adjacent to HR cells and hyphae. Distribution pattern of peroxidase corresponded to that of H2O2 in the infection sites of the incompatible interaction. The significance of the subcellular accumulation of ROS and peroxidase leading to cell wall modifications and HR is emphasized.