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RESEARCH PRODUCT

Active oxygen species production in tobacco cells elicited by cryptogein*

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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 could be, per se, the origin of the pH changes observed, we showed that it was not the main cause, since DPI and Tiron did not inhibit extracellular alkalinization. On the other hand, cryptogein-induced changes in pH could be abolished using fusicoccin (FC), which is known to stimulate the plasmalemma H + -ATPase. Consequently, the observed changes in pH induced by cryptogein could be mainly due to the inhibition of the plasmalemma H + -ATPase activity. Furthermore, changes in extracellular pH were shown to modulate the intensity of AOS production by elicited cells. The possible regulation of the NAD(P)H oxidase activity of plant cells by changes in pH is further discussed.