Cytoplasmic streaming and transport in the characean alga Nitella

Plasmodesmata were recorded in vivo in Nitella furcata using polarization and differential interference-contrast light microscopy, techniques that could prove useful for further physiological experimentation on intercellular transport in characean cells.Freeze-fractured, deep-etch replicas of Nitella endoplasm were prepared without the use of cryoprotective agents. The endoplasm, in which rapid cytoplasmic streaming occurs, contains intricate three-dimensional networks of filaments of which two prominent size classes are characterized: 7- to 8-nm putative actin filaments and 4- to 5-nm putative myosin filaments. It is quite likely that the putative actin filaments are components of the endoplasmic filaments, and that these filaments interacting with the 4- to 5-nm filaments produce the motive force generating the observed cytoplasmic streaming.