Oxidative burst and enzymatic antioxidant systems in rice plants during interaction with Alternaria alternata

In this research, 4 rice genotypes and 5 Alternaria alternata isolates were used to study the potential of Alternaria isolates obtained from various rice fields to infect the main rice cultivars planted in Iran and determine the levels of rice resistance to this fungus. Also, we investigated the role of reactive oxygen species (ROS), enzymatic antioxidants and lignin in basal resistance of rice to this necrotrophic fungus. Priming in H2O2 and O2− accumulation, peroxidase (POX) and superoxide dismutase (SOD) activity and lignification was observed in Shiroodi, as a partially resistant compared to the susceptible Domsiyah cultivar. Application of ROS generating systems increased disease development on both cultivars. In Shiroodi, elevation of O2− accumulation and SOD activity was observed at 12 h post inoculation (hpi) which was earlier than enhancement of H2O2 accumulation and POX activity at 24 hpi. In addition, application of SOD inhibitor reduced H2O2 and lignin levels and increased disease progress. Similarly, POX inhibitor reduced lignin content of the rice cells which was associated with increased disease index. In overall, both SOD and POX were associated with lignin formation, as a resistance mechanism in rice-A. alternata interaction. However, POX had prevailing function in lignification in our pathosystem.