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We recorded live, undifferentiated amebae of Dicfyostelium discoideum by video microscopy and analyzed the behavior of cytoplasmic particles and granules. Cytoplasmic streaming and saltatory movements are the two major types of particle movements that occur in interphase amebae. Saltatory movements predominated in an area around the nucleus-associated body (NAB) and many were radial toward or away from it, the velocity being very similar in both directions. Some saltations were simple forward movements, and others were complex toand-fro movements with as many as seven turnabouts. For a given leg of movement the velocity was not uniform along the path. Small particles (< 1 pm) moved faster (X = 2.8 pm/s) than large (-1 pm; R = 2.1 pmis) and very large (> 1 pm; X = 1.4 pm/s) particles, but the smallest particles were visible only in the running image and could not be analyzed. Ultrastructurally, saltating particles are digestive vacuoles and vesicles of various sizes, appearances, and contents, which are numerous particularly in the vicinity of the NAB. Several lines of evidence pointed to a role of microtubules (MTs) in saltatory particle movements. Composites of particle tracks corresponded closely to MT arrays visualized by immunofluorescence. No saltations occurred in mitotic amebae that lack cytoplasmic MTs, but the movements resumed toward the end of division, concurrently with the rebuilding of the complex of cytoplasmic MTs. Nocodazole reduced and eventually stopped saltatory movements over a period of 3 h, when aberrant MT patterns were the rule. Saltations in slime mold amebae may be an eye-catching feature of intracellular transport functioning in endo-and exocytosis in the shuffling of vesicles containing factors involved in ameboid movement, and in the transduction of external signals to the cell center.

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