Elicitor-stimulated ion fluxes and O 2 − from the oxidative burst are essential components in triggering defense gene activation and phytoalexin synthesis in parsley

Abstract

Fungal elicitor stimulates a multicomponent defense response in cultured parsley cells ( Petroselinum crispum ). Early elements of this receptor-mediated response are ion fluxes across the plasma membrane and the production of reactive oxygen species (ROS), sequentially followed by defense gene activation and phytoalexin accumulation. Omission of Ca 2+ from the culture medium or inhibition of elicitor-stimulated ion fluxes by ion channel blockers prevented the latter three reactions, all of which were triggered in the absence of elicitor by amphotericin B-induced ion fluxes. Inhibition of elicitor-stimulated ROS production using diphenylene iodonium blocked defense gene activation and phytoalexin accumulation. O 2 − but not H 2 O 2 stimulated phytoalexin accumulation, without inducing proton fluxes. These results demonstrate a causal relationship between early and late reactions of parsley cells to the elicitor and indicate a sequence of signaling events from receptor-mediated activation of ion channels via ROS production and defense gene activation to phytoalexin synthesis. Within this sequence, O 2 − rather than H 2 O 2 appears to trigger the subsequent reactions.