Responses of Cultured Tobacco Cells to Cryptogein, a Proteinaceous Elicitor from Phytophthora cryptogea: Possible Plasmalemma Involvement

In culture, the phytopathogenic fungus Phytophthora cryptogea secretes a protein which elicits hypersensitive-like necroses and protects tobacco plants against invasion by the pathogen Phytophthora parasitica var. nicotianae. This protein, named cryptogein, has been purified and its amino acid sequence determined. In this work, we studied the effect of cryptogein on tobacco cell suspension cultures. Cryptogein was lethal at about 0.10 micromolar. When added at sublethal doses, it elicited the production of ethylene and phytoalexins. It also induced a rapid increase in pH and conductivity of the extracellular medium without affecting the integrity of the plasma membrane. Cryptogein reduced the fusicoccin-induced acidification of the extracellular medium. The concentration which inhibited the fusicoccin response by 50% was 0.8 nanomolar, while 1 micromolar erythrosine B, an ATPase inhibitor, was needed to produce the same inhibition. However, cryptogein did not inhibit the activity of a purified plasma membrane ATPase. Results of binding studies with whole cells suggested the presence of elicitor-binding sites with a high affinity for cryptogein. The involvement of the plasma membrane during the initial interaction between elicitor and cells is discussed.