Fusicoccin Binding and Internalization by Soybean Protoplasts
Fusicoccin (FC) is a fungal toxin which binds to a receptor on the plasmalemma of higher plants causing hyperpolarization of the membrane potential and acidification of the apoplastic space (Feyerabend and Weiler 1989). In order to understand the fate of the toxin after its binding, we have developed an FC-containing probe which can be seen by light-or electron microscopy and can be quantified biochemically. The colloidal gold conjugate of bovine serum albumin covalently linked to FC (FC-BSA-Gold) binds to the plasmalemma of intact protoplasts and is partially internalized. Cells treated with FC-BSA-Gold are compared to control cells treated with the gold conjugate of BSA only (BSA-Gold), a marker for fluid-phase uptake. The amount and location of the gold label differ between FC-BSA-Gold and BSA-Gold treated protoplasts. When internalization of FC-BSA-Gold takes place, it may do so, in part, via receptor-mediated endocytosis. The technique described here will allow us to measure and visualize receptor-mediated endocytosis in plant cells.
KeywordsGold Label Fungal Toxin Apoplastic Space Gold Conjugate Total Incubation Time
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