Binding experiments using a 125I-labeled tyramine conjugate of N-acetylchitooctaose, a highly potent elicitor for the induction of phytoalexin production in rice cells, and a microsomal membrane preparation from suspension-cultured rice cells showed the presence of a novel high-affinity binding site for this oligosaccharide. The binding of the ligand was saturable and the Scatchard plot analysis of the results indicated the presence of a single class of binding site with a K d of 5.4 nM which is comparable with that reported for the binding of the hepta-β-glucoside elicitor in soybean membrane. The ligand binding was inhibited by unlabeled N-acetylchitoheptaose but not by its deacetylated form. These characteristics of this binding site coincide well with the specificity and sensitivity for the elicitor in several assay systems, suggesting the possible involvement of this binding site in the recognition of the elicitor in vivo.
