RAPID REACTIONS OF SPRUCE CELLS TO ELICITORS RELEASED FROM THE ECTOMYCORRHIZAL FUNGUS HEBELOMA CRUSTULINIFORME, AND INACTIVATION OF THESE ELICITORS BY EXTRACELLULAR SPRUCE CELL ENZYMES

Elicitors released from hyphae or cell walls of the ectomycorrhizal fu ngus Hebeloma crustuliniforme (Bull. ex Fries.) Quel. induced in suspe nsion-cultured cells of Picea abies (L.) Karst. a set of fast reaction s: (i) an immediate efflux of Cl- into the medium, followed by a K+ ef flux; (ii) an influx of Ca2+ (measured as accumulation of Ca-45(2+) in the cells); (iii) a phosphorylation of a 63-kDa protein and dephospho rylation of a 65-kDa protein (detectable by 4 min after elicitor appli cation); (iv) an alkalinization of the medium, and (v) a transient syn thesis of H2O2. The removal of extracellular Ca2+ by EGTA delayed the elicitor-induced alkalinization. A further reduction of this response could be achieved by TMB-8 an inhibitor of Ca2+ release from intracell ular stores. Moreover, the inhibition of protein kinase activity by st aurosporine prevented the extracellular alkalinization completely. How ever, the effectiveness of the elicitors in inducing the extracellular alkalinization was strongly impaired by constitutively secreted enzym es of spruce cells which cleaved the elicitors to inactive fragments. It is suggested that in ectomycorrhizae the efficacy of elicitors rele ased from fungal cell walls is controlled by apoplastic enzymes of the best; the plant itself is able to reduce the activity of fungal elici tors on their way through the plant cell wall. But those elicitors whi ch finally reach the plasma membrane of host cells induce reactions th at are similar to the early defense reactions in plant-pathogen intera ctions.