Unraveling the role of nitric oxide in regulation of defense responses in chilli against Alternaria leaf spot disease

Abstract: Alternaria leaf spot disease of chilli is an emerging problem in different chilli growing regions of the world including India. To understand the biochemical and molecular backbone of defense response against Alternaria alternata (A. alternata), two chilli cultivars (one tolerant and one susceptible) were selected. Different biochemical and histochemical methods were employed to understand the differential defense responses of two chilli cultivars in response to Alternaria invasion. Semiquantitative RT-PCR analysis showed higher transcript accumulation of different defense related genes in tolerant cultivar. The nitric oxide (NO) status was also monitored during activation of defense responses. In response to this fungus, reactive oxygen species (ROS) generation, callose deposition, cell death was also checked in both the cultivars. The tolerant cultivar showed enhanced defense responses (including NO) in response to the fungus, than that of susceptible cultivar. However, the tolerant cultivar showed reduced disease symptoms, lower amount of lipid peroxidation, lower amount of hydrogen peroxide (H2O2) generation and lower amount of cell death. In NO depleted condition pathogen induced defense responses were significantly compromised in both the cultivars. Overall, our present study provides a glimpse of NO participation in activation of defense responses in chilli against Alternaria invasion.