Biochemical changes in the leaves of wheat plants infected by Pyricularia oryzae

Blast, caused by the fungus Pyricularia oryzae, is a major disease of the wheat crop in the Brazilian Cerrado and represents a potential threat to world wheat production. However, information about the wheat-P. oryzae interaction is still limited. In this work, the activities of the enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), glutathione-S-transferase (GST), ascorbate peroxidase (APX), glutathione reductase (GR), and glutathione peroxidase (GPX) and the concentrations of superoxide (O₂(-)), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) as well as the electrolyte leakage (EL) were studied in wheat plants 'BR 18' and 'BRS 229', which are susceptible and partially resistant, respectively, to leaf blast at the vegetative growth stage, during the infection process of P. oryzae. The blast severity in BRS 229 was 50% lower than in BR 18 at 96 h after inoculation (hai). The activities of SOD, POX, APX, and GST increased for both cultivars in the inoculated plants compared with noninoculated plants and the increases were more pronounced for BRS 229 than for BR 18 at 96 hai. The GR and CAT activities only increased in inoculated plants from BRS 229 at 96 hai. For BR 18, the GR activity was not influenced by plant inoculation, and the CAT activity was lower in inoculated plants. The GPX activity only increased in inoculated plants from BR 18 at 48 and 72 hai. The P. oryzae infection increased the O₂(-), H₂O₂, and MDA concentrations and EL. However, the greater increases of the SOD, POX, APX, GST, GR, and CAT activities for BRS 229 compared with BR 18 contributed to the lower O₂(-), H₂O₂, and MDA concentrations and EL verified in the former. These results show that a more efficient antioxidative system in the removal of excess of reactive oxygen species generated during the infection process of P. oryzae limits the cellular damage caused by the fungus, thus contributing to greater wheat resistance to blast.