Apoplastic oxidative defenses during non-host interactions of tomato (Lycopersicon esculentum L.) with Magnaporthe grisea

Abstract

Rapid production of reactive oxygen species (ROS) at the apoplast is one of the fastest and the earliest active defense responses against pathogen attack in plants. The aim of the study was to investigate the intensity and timing of the ROS formation, lipid peroxidation and activity of antioxidant enzymes as initial responses of tomato (Lycopersicon esculentum L. cv. Money maker) against the non-host pathogen Magnaporthe grisea. Histological observations revealed that non-host resistance of tomato against M. grisea is associated with the deposition of callose and hypersensitive cell death. The concentration of hydrogen peroxide (H₂O₂) and hydroxyl radicals (·OH) increased during early hours of inoculation, i.e., 24 hour post inoculation (hpi) and 12 hpi, respectively. Superoxide radicals (O₂⁻) increased at 48 hpi in M. grisea-challenged tomato leaves. The activity of the antioxidant enzymes like superoxide dismutase and guaiacol peroxidase increased by 72 hpi in M. grisea-challenged leaves. NADH peroxidase activity was higher at 12 hpi in M. grisea-challenged tomato leaves compared to mock-inoculated leaves. The oxidative burst generated during the non-host interactions of tomato with M. grisea appears to be an early first line of defense by the tomato plants mounted against the invading non-host pathogen. Physical barriers like deposition of callose and hypersensitive cell death were induced by ROS like H₂O₂ and ·OH at early hours, followed by an increase in the activity of antioxidant enzymes contributed to non-host resistance of tomato against M. grisea.