Rapid Communication

Involvement of reactive oxygen species has been implicated in plant defence against pathogens. We report here a novel pathway of H2O2 generation induced by the addition of phosphate in soybean (Glycine max L.) cell suspension cultures. This H2O2 generation was initiated shortly after the addition of phosphate, and lasted only approximately one hour, as opposed to several hours observed during an attack by an avirulent strain of the bacterial pathogen Pseudomonas syringae pv. glycinea (Psg). In addition, when cell cultures were treated with both phosphate and the avirulent pathogen, two distinct oxidative burst events were observed. In contrast to DPI-sensitive Psginduced H2O2 generation, phosphate-induced H2O2 generation was insensitive to this NADPH oxidase inhibitor. This suggests that an NADPH oxidase-independent pathway may be involved in the phosphate-induced H2O2 accumulation, which could be involved in sensing of phosphate availability in the environment.