Action of taxol on mitosis: modification of microtubule arrangements and function of the mitotic spindle in Haemanthus endosperm.

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Abstract
The effect of taxol on mitosis in Haemanthus endosperm was studied. Immuno-gold stain (IGS), a new immunocytochemical method, was used to visualize microtubules (MT) in the light microscope. Observations on MT arrangements were correlated with studies in vivo. Chromosome movements are affected in all stages of mitosis which progresses over at least 104 range of taxol concentrations. The 3 most characteristic effects on MT are: enhancement of the lateral associations between MT, seen especially during the reorganization of the polar region of the spindle, promotion of MT assembly, leading to the formation of additional MT in the spindle and MT arrays in the cytoplasm and an increase in MT stability, demonstrated in their increased cold resistance. Emphasis was placed on the primary, immediate effects, occurring in the first 30 min of taxol action. Effects are detected after a few minutes, are reversible and are concentration/time dependent. The spindle and phragmoplast are remarkably modified due to the enhancement of lateral associations of MT and the formation of abundant nonkinetochore and polar, asterlike MT. The equatorial region of the interzone in anaphase may be entirely depleted of MT and the spindle may break perpendicularly to the spindle axis. Mitosis is completed in these conditions, providing evidence for the motile autonomy of each half-spindle. Trailing chromosome arms in anaphase are often stretched and broken. Chromosome fragments are transported away from the polar regions, i.e., in the direction opposite to that expected. This supplies the 1st direct evidence of pushing by elongating MT in an anastral higher plant spindle. The relation between the lateral association of MT ends to assembly/disassembly and the role of such an interaction in spindle function and organization were emphasized.