Cytochalasin‐Induced reorganization of actin in allium root cells

The effect of cytochalasins on F‐actin was investigated in Allium root cells stained with rhodamine‐phalloidin. With cytochalasin D (CD), the normal interphase network of actin fibers is replaced by dispersed rods and specks similar to those seen in animal cells. However, during division, the specks accumulate at the poles in the form of one to a few large aggregates. The effects intensify with increasing concentration (0.5–5 m̈g/ml) and exposure time (0.5–3 hr). Further, similar behavior is observed with cytochalasin B, but dihydroCB has little effect. Double localizations show that during preprophase, aggregates cluster in association with microtubule foci at the new poles located near the nuclear envelope. From metaphase through anaphase, the aggregates are often found near the tips of kinetochore fibers, while in telophase they are often appressed to the pole side of the daughter nuclei. No association is seen between actin and the other microtubule arrays. The reorganization of F‐actin into small specks is unaffected by sodium azide, but aggregation at the poles is very sensitive to this agent. Polar clustering is also blocked by oryzalin, colchicine, and isopropyl n‐(3‐chlorophenyl) carbamate, but taxol has no effect. Experiments with scleroderma serum 5051 show that CD‐induced aggregates are embedded in centrosomal material at the poles. The results reveal that the reorganization of actin in response to cytochalasins differs during the cell cycle. Furthermore, the aggregation of actin during division is probably governed by an energy‐dependent interaction with microtubules.