Differences in the induction of the oxidative burst in compatible and incompatible interactions of soybean and Phytophthora sojae

The effect of infection by Phytophthora sojae on the oxidative state in the soybean cultivars Nannong 493-1 (medium-resistant) and Hefeng 35 (susceptible) was studied. Pro-oxidant activity (H2O2 production and lipid peroxidation) and antioxidant systems (enzymatic activities of catalase and glutathione reductase, and low-molecular-weight antioxidants such as reduced ascorbate and glutathione) along with cell death and pathogenesis-related (PR) protein analyses were performed to examine their roles in establishing resistance or susceptibility. During pathogen infection, H2O2 accumulation was higher in the soybean cultivar Nannong 493-1 than in Hefeng 35. Cell death was more severe in Nannong 493-1 during the early infection period. However, the malondialdehyde levels were higher in Hefeng 35 than in Nannong 493-1 in the late experiment period. The inherent levels of the antioxidant systems were not consistently higher or lower in Nannong 493-1 than in Hefeng 35 under different pathogen infection duration or antioxidation parameters. The expression of the PR genes induced by pathogen infection varied with the cultivar and the pathogen-infection process. Exogenous treatment of soybean with one of three reductants (dithiothreitol, reduced ascorbate, or glutathione) facilitated the disease caused by P. sojae in both cultivars. In general, these results show that reactive oxygen species play an important role in the interactions of soybean and P. sojae.