Hydrogen peroxide formation in C. annuum cell suspension cultures upon elicitation with supernatant of an X. campestris pv. campestris exbD2 mutant co-incubated with cell wall material. To assess the role of the exbD2 gene in provoking defense reactions in non-host plants, cultures of the X. campestris pv. campestris mutant strain B100-11.03 were co-incubated with cell wall material from C. annuum. Then the formation of H2O2 was monitored in cell suspension cultures of C. annuum upon the addition either supernatants of X. campestris pv. campestris wild-type cultures (●), supernatants of X. campestris pv. campestris cultures affected in exbD2 that were co-incubated with C. annuum cell wall material (♦), invertase as a positive control (■), or C. annuum cell wall material employed as negative control (✶). The mutated bacterial mutant strain deficient in exbD2 could not evoke an oxidative burst reaction.