Novel actin rods appeared in spores of Dictyostelium discoideum.

When spores of Dictyostelium discoideum matured through normal development were stained with rhodamine-phalloidin, rod-shaped fluorescence was found across the nucleus and in the cytoplasm. Electron micrographs of the rod shape showed that it consisted of long and straight fibers 12 nm in diameter. In contrast, a conventional actin rod, which usually is formed under stress conditions, is composed of short filaments 6 nm in diameter, and cannot be stained with fluorescent phalloidin. Hence it can be inferred that the structure appeared in Dictyostelium spores under no stress conditions is a novel actin rod.