ASSOCIATION OF MICROTUBULES WITH THE PLASMA-MEMBRANE OF TOBACCO BY-2 CELLS IN-VITRO

Membrane ghosts prepared from tobacco BY-2 cells bound microtubules (M Ts) that had been assembled in an extract of evacuolated protoplasts o f the same cells and, as a result, the number of MTs on the ghosts inc reased. MTs that had formed on the ghosts after incubation with the ex tract were more sensitive to cold-treatment than the preexisting MTs. Binding of MTs was also observed on ghosts that had been treated with a cold solution of Ca2+ to remove preexisting MTs. This result suggest s that a system that mediated the binding of MTs to the plasma membran e remained on the ghosts. No binding of MTs was observed to ghosts tha t had been treated with trypsin. Preexisting MTs were removed by treat ment with 0.6 M KCl or 0.1 M Na2CO3. Membrane ghosts treated with KCl or Na2CO3 did not bind MTs that had been assembled in the extract in t he absence of taxol. However, ghosts prepared in the same way did bind MTs that had been assembled in the extract in the presence of taxol. It seems that treatment with KCl or Na2CO3 removes a component(s) from the system that mediates the binding of MTs to the plasma membrane an d that a factor(s), associated with MTs assembled in the extract in th e presence of taxol, compensates for the loss of this component(s) fro m the system.