Microtubule dynamics determine chromosome lagging and transport of acentric fragments.

The general direction of transport of spindle inclusions including acentric chromosome fragments during mitosis in endosperm of the higher plants Haemanthus is predictable and stage-dependent. Their segregation is random and they are usually eliminated from the spindle. This transport is superimposed on normal chromosome segregation. Thus, there are 2 superimposed mitotic transports: one which distributes kinetochores and the other which distributes spindle inclusions. The functional relation of these 2 transports to each other is not well understood. However, due to this 'non-kinetochore transport,' fragments may persist a few consecutive divisions before being permanently eliminated from the nucleus. Malfunction of kinetochores of any chromosome, resulting in the loss of their anchorage within the spindle, subjects them to 'non-kinetochore' transport and nearly certain, permanent elimination from the spindle. Additionally, experimental evidence presented here demonstrates that rapid polymerization (elongation) of microtubules may desynchronize anaphase and cause lagging of whole chromosomes. This may be one more, previously unconsidered, factor which may cause the malfunction of the kinetochore fiber and consequent elimination of one or a few chromosomes from the spindle.