Active oxygen species production in tobacco cells elicited by cryptogein*

We analyse the relationship between active oxygen species (AOS) production and pH changes induced in tobacco cells by cryptogein, a fungal proteinaceous elicitor of defence mechanisms in plants. When tobacco cells were treated with cryptogein, an intracellular acidification, an alkalinization of the extracellular medium and a transient burst of AOS (H 2 O 2 ) were observed. Treatment of elicited cells with either diphenyleneiodonium (DPI), an inhibitor of the neutrophil NADPH oxidase, or Tiron, which scavenges O2 - , abolished AOS production. These data suggest the involvement of a NADPH oxidase-like enzyme leading to H 2 O 2 production through O 2 - dismutation. Although H 2 O 2 production…