EXTENSIVE GENE DUPLICATIONS IN DIPLOID EUPATORIUM (ASTERACEAE)

An electrophoretic study of isozyme number for seven soluble enzymes revealed extensive gene duplications in eight diploid species of American Eupatoriumbelonging to three morphological groups. The enzymes isocitrate dehydrogenase, phosphoglucomutase, phosphoglucose isomerase, 6‐phosphogluconate dehydrogenase, and shikimate dehydrogenase occur as three to six isozymes in all species, whereas the minimal conserved number typical of diploid plants is two isozymes for each. Fructose 1, 6‐biphosphate aldolase is expressed as multibanded pattern suggesting fixed heterozygosity in all examined species. It was not possible to document gene duplication for triosephosphate isomerase from the electrophoretic patterns. All species examined have a chromosome number of 2n= 20, which has been regarded as the basic diploid number for Eupatorium.However, the detection of extensive duplications suggests that 2n= 10 may be the original diploid chromosome number in Eupatoriumand that plants with 2n= 20 are of polyploid origin. This hypothesis would mean that extensive duplications at isozyme gene loci have been maintained since the origin of the genus, despite chromosomal diploidization having occurred.