Dissection of the ozone-induced calcium signature

The cellular responses of plants to numerous extracellular stimuli are medi ated by transient elevations in the concentration of cytosolic free calcium ([Ca2+](cyt)). We have addressed the question of how cells can use this ap parently ubiquitous system to initiate so many specific and appropriate end responses. We show that the pollutant gas ozone elicits a biphasic Ca2+ re sponse in intact Arabidopsis plants and a subsequent increase in expression of the gene encoding the antioxidant defence enzyme glutathione-S-transfer ase (GST). The second of the two [Ca2+](cyt) peaks, but not the first, coul d be eliminated either by pre-treatment of plants with lanthanum chloride, or by reducing the duration of ozone fumigation. Under these conditions, oz one-induced GST expression was abolished. These data provide a functional d issection of the ozone Ca2+ signalling pathway and indicate that the second ozone-induced [Ca2+](cyt) peak provides the necessary information to direc t expression of GST.