Suramin inhibits oxidant signalling in tobacco suspension-cultured cells

Plant cells respond to ultraviolet radiation and other oxidant-generating agents by mobilizing cellular defences, but the signal network linking perception of redox perturbation with defence remains unknown. Irradiation of tobacco suspension-cultured cells with UVC was found to induce the activation of a specific MAPK(46) (salicylic acid-induced protein kinase) within 1 min. To explore where UVC and other oxidants might initially act to trigger this signal response, we employed suramin, a non-membrane-permeable reagent that interferes with membrane receptor-mediated signalling in mammalian cells. Pre-treatment of tobacco cells with suramin strongly attenuated the UVC-induced activation of MAPK(46) in a concentration-dependent manner. Suramin was also able to interdict both ozone- and hydrogen peroxide-induced activation of MAPK(46), indicating that reactive oxygen species (ROS) signalling to the MAPK cascade in general may be initiated at the cell membrane, perhaps through oxidative activation of membrane receptors.