Abstract: Abstract：【Objective】To elucidate a key role for nitric oxide (NO) played during rice-Xanthomonas spp interactions by triggering hypersensitive cell death (HCD) and inducing defense genes.【Method】NO production and defense gene expression in rice suspension-cultured cells was compared after inoculations with X. campestris pv. vesicatoria (Xcv), a non-host bacterial pathogen and X. oryzae pv. oryzae (Xoo), the bacterial blight pathogen of rice. 【Result】NO burst, activation of nitric oxide synthase (NOS), expression of NO synthesis-related genes (nos and nr) and defense-related genes (pal, pox and gst) was found to be significantly induced by Xcv, not by Xoo. Application of NO scavenger PTIO or co-inoculation of Xcv with Xoo resulted in the significant suppression of Xcv-induced gene expression.【Conclusion】Xcv induces defense gene expression and HCD of rice suspension cultures through a NO-dependent signal pathway, whereas Xoo inhibits NO-mediated defense gene expression and HCD by suppressing NO production and detoxifying NO.

Key words: rice, Xanthomonas spp., nitric oxide, defense gene expression, hypersensitive cell death