Binding of the phytotoxin zinniol stimulates the entry of calcium into plant protoplasts.
Zinniol [1,2-bis(hydroxymethyl)-3-methoxy-4-methyl-5-(3-methyl-2-butenyloxy)benzene], a toxin produced by fungi of the Alternaria group, causes symptoms in plants that resemble those induced by the fungi. The phytotoxin binds to carrot protoplasts and isolated membranes in a saturable and reversible manner. Receptor occupancy stimulates entry of calcium into protoplasts. Zinniol can partially reverse the effects and binding of the calcium-channel blockers desmethoxyverapamil and bepridil. Selected cell lines that are insensitive to zinniol lose part of their binding capacity and sensitivity to the action of the agonist-like compound but are still able to bind calcium-channel blockers. We conclude that zinniol acts on calcium entry but that the targets of the toxin and of calcium-channel blockers are dissimilar, suggesting the occurrence of sites affected both by zinniol and by channel blockers and of sites affected only by zinniol.
Centre de Physiologie Végétale, Université Paul Sabatier, Centre National de la Recherche Scientifique Unité Associée 241, 118 route de Narbonne, F-31062 Toulouse Cédex, France.
P
P
Thuleau
A
A
Graziana
M
M
Rossignol
H
H
Kauss
P
P
Auriol
R
R
Ranjeva