Continuous production of extracellular antioxidants in suspension cells attenuates the oxidative burst detected in plant microbe interactions

Suspension cells of Solanacearum tuberosum and Nicotiana tabacum placed in fresh buffer rapidly produce and maintain significant pools of extracellular antioxidants. The extracellular antioxidant was detected by first adding a known amount of exogenous H2O2 to samples and then immediately measuring the remaining H2O2. The difference between the amount added and amount remaining was used to determine the antioxidant capacity of the sample. This extracellular antioxidant pool attenuates levels of hydrogen peroxide produced during plant–bacterial interactions. When tobacco cells were inoculated with an isolate Pseudomonas syringae pv. syringae that causes a hypersensitive response much of the antioxidant capacity had been expended neutralizing the oxidative burst characteristic of such plant–microbe interactions. After a brief delay, the levels of extracellular phenolics increased commensurate to antioxidative capacity in freshly transferred cells within 2–4 h. The strong UV absorbance of these extracellular phenolics within 250 and 350 nm was used to follow oxidation upon reaction with H2O2. This extracellular antioxidant pool is an important consideration in cell suspension studies of the plant–microbe oxidative burst. This study demonstrates that the true magnitude and timing of the oxidative burst in cell suspensions is masked by extracellular antioxidants.