Abstract: Oryza meyeriana， a wild rice species， is highly resistant to rice bacterial blight （BB）， but the resistance mechanism is still unknown. Nitric oxide （NO） is an important signaling molecule that plays a pivotal role in plant disease resistance responses. However， little study has focused on whether NO is involved in BB resistance of O. meyeriana. In this study， the effects of BB pathogen inoculation on leaf lesion， NO content， NO subcellular location and xylem ultrastructure were studied in O. meyeriana and a susceptible rice cultivar Nipponbare. Pathogen infection caused yellow necrotic lesions in Nipponbare and brown apoptotic lesion in O. meyeriana， and the lesion length was much longer in Nipponbare than in the wild rice. No difference was found in NO content in Nipponbare after pathogen inoculation. However， NO content was prominently increased by pathogen inoculation in the wild rice， and it was further discovered that NO was largely accumulated in xylem cell wall. In addition， electron microscopic observations showed that BB pathogen inoculation induced the thickening of xylem cell wall in O. meyeriana but not in Nipponbare. Based on these results， we suggested that NO played an important role in the BB resistance of O. meyeriana， and the role might involve the thickening of xylem cell wall that could inhibit further invasion of the pathogen.

Key words: Oryza meyeriana, rice bacterial blight, nitric oxide, subcellular location, cell\|wall thickening