Origin of Chromosome Number Variation in Cultured Plant Cells

CULTURED cells of both animal and plant tissues are characterised by instability of chromosome number and structure 1,2 . Although there is evidence 3 that polyploid plant cell lines may arise from endoreduplicated nuclei in the original explant, the range of chromosome number and structure observed in established cultures strongly points to the origin of these changes during culture. Since the precise distribution of chromosomes at mitotic anaphase is the essential prerequisite for chromosome number stability 5 , this seems the most likely point at which instability could be induced in culture. It has been shown 6,7 that, in culture, animal cells of various species are characterised by the presence of multipolar mitoses, a feature which would produce daughter nuclei with aneuploid chromosome numbers. Such multipolar mitoses have been briefly noted for plant tissue cultures 8,9 but their frequencies have not been quantified.