Ia. Dubery et R. Meyer, SPECIFIC BINDING OF A VERTICILLIUM-DAHLIAE PHYTOTOXIN TO PROTOPLASTS OF COTTON, GOSSYPIUM-HIRSUTUM, Plant cell reports, 15(10), 1996, pp. 777-780
The occurrence of specific, high-affinity binding sites for a protein-
lipopolysaccharide (PLP) phytotoxin purified from culture filtrates of
a virulent Verticillium dahliae isolate has been demonstrated in cott
on protoplasts. Binding of the I-125-radiolabelled PLP-complex to prot
oplasts from cotyledon tissue was saturable and with an affinity (K-d
= 17.3 nM) comparable with the concentration required for biological a
ctivity. A single class of binding site, accessible at the surface of
the intact protoplasts, was found and the maximal number of binding si
tes were estimated as 2.41x10(-16) moles per protoplast. The binding a
ffinity to protoplasts proved near identical to that found with purifi
ed plasma membrane fractions from roots. When cultivars exhibiting res
istance or susceptibility towards the pathogen were compared, no signi
ficant differences were found in the affinity of binding, but five tim
es as many binding sites per protoplast and sixteen times as many bind
ing sites per mg membrane protein were found in the resistant cultivar
.