Early signalling events in the apoplastic oxidative burst in suspension cultured French bean cells involve cAMP and Ca2+

Modulators of cAMP, calcium and CI proteins were used to treat bean (Phaseo lus vulgaris) cells before addition of an elicitor from Colletotrichum lind emuthianum in order to elucidate the early steps of signal transduction lea ding to the production of the apoplastic oxidative burst. Hydrogen peroxide production by elicited bean cells was monitored with lumi nol-or xylenol-orange-based assays. Pretreatment with forskolin, dibutyryl cAMP or the Ca2+ ionophore A23187 en hanced the production of reactive oxygen species (ROS). The Ca2+ channel bl ocker, verapamil, and the calmodulin antagonist W7 led to a decreased oxida tive burst and cancelled the dibutyryl cAMP effect. The production of ROS w as increased by cholera toxin (CTX), an activator of G proteins. Thus, an increase of cytosolic calcium ([Ca2+](cyt)) mediated through an in creased level of cAMP is required for ROS production. The data support a ro le for CI proteins and cAMP in extracellular alkalinization and Ca2+ influx , possibly in the provision of a reductant, which with the extracellular pe roxidase, are required for the apoplastic oxidative burst. (C) New Phytolog ist (2001) 151. 185-194.