Comparison of binding properties and early biological effects of elicitinsin tobacco cells

Elicitins are a family of small proteins secreted by Phytophthora species t hat have a high degree of homology and elicit defense reactions in tobacco (Nicotiana tabacum). They display acidic or basic characteristics, the acid ic elicitins being less efficient in inducing plant necrosis. In this study we compared the binding properties of four elicitins (two basic and two ac idic) and early-induced signal transduction events (Ca2+ influx, extracellu lar medium alkalinization, and active oxygen species production). The affin ity for tobacco plasma membrane-binding sites and the number of binding sit es were similar for all four elicitins. Furthermore, elicitins compete with one another for binding sites, suggesting that they interact with the same receptor. The four elicitins induced Ca2+ influx, extracellular medium alk alinization, and the production of active oxygen species in tobacco cell su spensions, but the intensity and kinetics of these effects were different f rom one elicitin to another. As a general observation the concentrations th at induce similar levels of biological activities were lower for basic elic itins (with the exception of cinnamomin-induced Ca2+ uptake). The qualitati ve similarity of early events induced by elicitins indicates a common trans duction scheme, whereas fine signal transduction tuning is different in eac h elicitin.