Nitrite and nitric oxide are important in the adjustment of primary metabolism during the hypersensitive response in tobacco

Nitrate and ammonia deferentially modulate primary metabolism during the hypersensitive response in tobacco. Tobacco RNAi line with low nitrite reductase (NiRr) levels were used to investigate the roles of nitrite and nitric oxide (NO) in this process. This line accumulates NO2-, with increased NO generation, but allows sufficient reduction to NH4+ to maintain plant viability. Inoculation of the NO3- grown wild type and NiRr plants with the non-host biotrophic pathogen Pseudomonas syringae pv. phaseolicola induced an accumulation of nitrite and NO, together a hypersensitive response (HR) that resulted in decreased bacterial growth, increased electrolyte leakage and enhanced pathogen resistance (PR) gene expression. These responses were higher with increase in NO/ NO2- levels in NiRr plants than WT under NO3- nutrition. In contrast NH4+ grown WT and NiRr plants exhibited compromised resistance. A metabolomic analysis detected 141 metabolites, whose abundance was differentially changed as a result of exposure to P. syringae pv and in response to NO/ NO2- accumulation Of these, 13 were involved in primary metabolism and most were linked to amino acid and energy metabolism. HR-associated changes in metabolism that are often linked with primary nitrate assimilation may therefore be influenced by nitrite and NO production