HIGH-AFFINITY BINDING-SITE FOR ETHYLENE-INDUCING XYLANASE ELICITOR ONNICOTIANA-TABACUM MEMBRANES

Challenge of Nicotiana tabacum cv Xanthi with the ethylene inducing xy lanase (EIX) from Trichoderma viride causes rapid induction of plant d efense responses leading to hypersensitive necrosis. This phenomenon i s cultivar-specific; no response is detected when N. tabacum cv Hicks is similarly treated. The responsiveness is determined in tobacco and tomato by a single dominant gene. EIX was labeled with fluorescein-iso thiocyanate and incubated with cell suspension cultures, protoplasts o r microsomal membranes. Binding of EIX to the microsomal membranes was found to be specific and saturable, with a dissociation constant of 6 .2 nM. Using confocal laser microscopy, the EIX binding site was local ized to the plasma membrane. Binding of EIX to its high-affinity site occurred in responsive species. These results demonstrate the existenc e of a high-affinity binding site for EIX on the plasma membrane of re sponsive cultivars. Chemical cross-linking of EIX to microsomal membra nes from responding plants revealed a 66 kDa protein complex. This pro tein may function as the receptor that mediates the hypersensitive res ponse induced by EIX binding.