Direct visualization of organelle movement along actin filaments dissociated from characean algae.

A system has been developed in which organelle transport can be studied without the influence of an organized cellular cytoplasm. Binding and continuous unidirectional movement of organelles along isolated cellular transport cables were directly visualized by video light microscopy after the dissociation of the cytoplasm of characean algae cells in a Ca2+-free buffer containing adenosine triphosphate. Individual organelles had more than one attachment site and moved at mean rates of 11.2 or 62.1 micrometers per second along multiple parallel pathways on each cable. Electron microscopy of these cables after direct freezing demonstrated that they consist of compact bundles of actin filaments. Under these conditions, characteristics of organelle movement should reflect directly the underlying molecular processes of binding and force generation.