Induction of redox sensitive extracellular phenolics during plant–bacterial interactions

This study focuses on the transient and complex nature of phenolics that accumulate in the extracellular environment of plant suspension cells during the first few hours of the interaction between these plant cells and bacterial pathogens. Using suspension cells of Nicotiana tabacum we identified four acetophenones and four hydroxycinnamic acid amides that accumulate in this extracellular environment. Treatment of the suspension cells with isolates of the plant pathogen Pseudomonas syringae or heat-killed bacteria increased elicitation of extracellular phenolics and changed the composition of the compounds that accumulated. These phenolics were sensitive to oxidative stress; when suspension cells were treated with bacterial strains or elicitors that triggered an oxidative burst, these phenolics were oxidized and depleted for the duration of the burst. The qualitative and quantitative makeup of phenolics produced by N. tabacum suspensions was also affected by plant cell age and density. To our knowledge, this is the first study that closely follows the kinetics of individual extracellular phenolic compounds and the concurrent oxidative stress during the first few hours of a plant–bacterial interaction.