The karyotype of the grass Zingeria biebersteiniana (2n = 4) by light and electron microscopy

Abstract

The grass Zingeria biebersteiniana is one of only four angiosperm and two monocotyledonous species known with 2n = 4. Its 4C nuclear DNA amount, 7.4 pg, is similar to that of Haplopappus gracilis (4C = 8.2 pg), a dicotyledonous species with 2n = 4. Studies of the karyotype of Z. biebersteiniana using the electron microscope three-dimensional serial thin section reconstruction method showed it to be a highly suitable material in which to examine chromosome placement. Although the two chromosome types have very similar relative volumes (53 and 47%, respectively) and arm volume ratios (1.08 and 1.13, respectively), nevertheless, each chromosome are each arm could be reliably distinguished in single reconstructed cells at each stage of mitosis. Thus, the short arm of chromosome 1 was identified by its unique lighter stained nucleolus organizer region, while the short arm of chromosome 2 was distinguished from the long arm by its relatively smaller arm volume. The two chromosomes and their arms were also easily distinguished at mitotic metaphase in the light microscope by two diagnostic C-bands, one at the telomere of the short arm of chromosome 1 and the other near to, but not at, the short arm telomere of chromosome 2.Key words: Zingeria biebersteiniana (2n = 4), low chromosome number.