High-affinity binding of a protein-lipopolysaccharide phytotoxin from Verticillium dahliae to cotton membranes.

The presence of a specific binding site for a protein-lipopolysaccharide (PLP) phytotoxin isolated from culture filtrates of Verticillium dahliae has been demonstrated in plasma membranes from cotton seedlings. The 125I-labelled PLP was used as a ligand in binding assays with plasma membrane enriched fractions. Root tissue exhibited the highest amount of binding activity compared to hypocotyl and cotyledon tissue. Binding of the [125I]PLP was saturable, reversible, and with an affinity (Kd = 1.42 x 10(-8) M) comparable with the concentration required for biological activity. A single class of binding site was found, and the maximal number of binding sites were estimated as 5.4 x 10(-15) mol/micrograms protein.