Localization of actin filaments in internodal cells of characean algae. A scanning and transmission electron microscope study.

New methods of visualizing subcortical actin filament bundles, or fibrils, in Characean internodes confirm that they are associated with chloroplasts at the surface facing the streaming endoplasm, and reveal that they are continuous over long distances. With the scanning electron microscope, an average of four to six fibrils are seen bridging a file of chloroplasts. The same configuration appears in negatively stained preparations of large blocks of chloroplast files connected by actin fibrils. Few branches of the subcortical fibrils are evident. These findings are discussed with respect to the mechanism of cytoplasmic streaming in Characeae.