Analysis and effects of cytosolic free calcium increases in response to elicitors in Nicotiana plumbaginifolia cells

Cell suspensions obtained from Nicotiana plumbaginifolia plants stably expressing the apoaequorin gene were used to analyze changes in cytosolic free calcium concentrations ([Ca2+](cyt)) in response to elicitors of plant defenses, particularly cryptogein and oligogalacturonides. The calcium signatures differ in lag time, peak time, intensity, and duration. The intensities of both signatures depend on elicitor concentration and extracellular calcium concentration. Cryptogein signature is characterized by a long-sustained [Ca2+](cyt) increase that should be responsible for sustained mitogen-activated protein kinase activation, microtubule depolymerization, defense gene activation, and cell death. The [Ca2+]. increase in elicitor-treated cells first results from a calcium influx, which in turns leads to calcium release from internal stores and additional Ca2+ influx. H2O2 resulting from the calcium-dependent activation of the NADPH oxidase also participates in [Ca2+](cyt) increase and may activate calcium channels from the plasma membrane. Competition assays with different elicitins demonstrate that [Ca2+](cyt) increase is mediated by cryptogein-receptor interaction.