Fusicoccin Activity and Binding in Arabidopsis thaliana

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Abstract
I have examined the activity and specific binding of the phytotoxin fusicoccin [produced by Fusicoccum amygdali] using Arabidopsis thaliana L. Col-O. Fusicoccin (10 micro-molar) stimulates both proton extrusion and enlargement in isolated Arabidopsis leaf discs. Radiolabeled fusicoccin specifically binds to membranes (13,000 to 100,000 g subcellular fraction) from cultured cells of Arabidopsis. The specific binding of this phytotoxin to putative receptor sites in Arabidopsis membranes is both pH-sensitive (pH optimum = 5.5 to 6.0) and heat-labile (10 min at 70.degree. C). The apparent dissociation mutant for the specific binding at 20 .degree. C is approximately 1.3 .times. 10-8 molar. The results of this study are in general agreement with previous reports of fusicoccin binding and activity in other plant species.