Effects of catalase on the accumulation of H2O2 in rice cells inoculated with rice blast fungus, Magnaporthe oryzae

Roles of H2O2 in the infection process of Magnaporthe oryzae on rice were investigated. In a leaf sheath assay for up to 48 h post-inoculation, the absence or presence of catalase in the conidia suspension was correlated with the level of accumulated H2O2 in infected leaf cells, as observed by staining with 3',3-diaminobenzidine tetrahydrochloride. In the incompatible interaction, the appearance of autofluorescence or frequency of cell death characterized by granulation (symptoms characteristic of hypersensitive responses) was not significantly affected by the presence of catalase in the conidia suspension. In the leaf blade assay, inoculation of compatible conidia in the presence of catalase produced more severe symptoms than that of conidia in the absence of catalase at 6 days post-inoculation. These results suggest that, in this host-parasite interaction, the primary role of host-produced H2O2 is in limiting hyphal growth after penetration through toxic action. Furthermore, in incompatible interactions, H2O2 is implied not to be a major mediator of hypersensitive cell death.