Elucidating oxidative burst during interaction of rice-elicitor/pathogen (Xanthomonas oryzae pv. Oryzae)

The oxidative burst is one of the earliest and most prominent defence responses of plants to microbial infection and is characterized by a rapid and transient accumulation of reactive oxygen species (ROS), including hydrogen peroxide (H ₂ O ₂ ). The present study investigated the timing and magnitude of ROS production and associated antioxidant enzyme responses in five rice cultivars (TN-1, Satabdi, Naveen, Annapurna, and Tapaswini) following treatment with two defence elicitors, salicylic acid (SA) and chitosan (CH), and infection with the bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo). Xoo-inoculated plants exhibited a biphasic oxidative burst, marked by an early increase in H ₂ O ₂ accumulation at 24 h post-inoculation (hpi), followed by a second, more sustained phase after 72 hpi. Enhanced lipid peroxidation accompanied ROS generation, indicating oxidative stress during pathogen interaction. Superoxide anion (O ₂ •⁻) and hydroxyl radical (•OH) levels increased predominantly between 72 and 120 hpi, depending on the cultivar. Antioxidant capacity, assessed by DPPH radical scavenging activity, increased following pathogen inoculation. Enzymatic antioxidants showed dynamic responses, with superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) activities being differentially regulated across cultivars and time points, particularly during the later stages of infection. The early oxidative burst is consistent with PAMP-triggered immunity (PTI), while the sustained ROS accumulation at later stages may reflect prolonged defence signalling or pathogen proliferation during a compatible interaction. Both SA and CH acted as PTI mimics, inducing ROS production and activating antioxidant defence mechanisms. Collectively, these findings highlight the role of oxidative burst dynamics and antioxidant regulation in rice defence responses against bacterial blight.