Cryptopolyploidy in Bunias (Brassicaceae) revisited - a flow cytometric and densitometric study

摘要

The concern of the present analysis is the hypothetical 'cryptopolyploidy', a concept basically of historical interest only, but discussed again recently in a 1996 treatment of the term and its historical background. Previous workers, while studyingchromosomes in Bunias erucago and B. orientalis, found 2n = 14 in both species but twice the chromosome volume in B. erucago compared with B. orientalis. This was considered 'cryptopolyploidy' in B. erucago, i.e., pairwise fused chromosomes on a tetraploid basis or endoreduplicated (and thus binemic) chromosomes in this species. Cryptopolyploidy has also been claimed in Vinca difformis (Vincaceae). The term 'cryptopolyploidy' has been criticised previously because, it is considered that the genuinely polyploid status of these plants is not hidden ('crypto') but phenotypically (from herbarium specimens) recognizable. The term 'phenopolyploidy' was coined, i.e., "phenotypic polyploidy disagreeing with the karyotype numerically evaluated". In the presentstudy, genome size of B. orientalis and B. erucago (both 2n = 14) was measured by Feulgen densitometry and propidium iodide flow cytometry. Surprisingly, B. erucago (the annual species with 2.13 pg, 1C) turned out to have only 0.81-fold the DNA amount of B. orientalis (the perennial species with 2.64 pg, 1C). Therefore, any kind of genetically polyploid status in B. erucago is out of the question. Only speculative significance can be ascribed to the terms 'cryptopolyploidy' and 'phenopolyploidy'.