Karyotype analysis and heterochromatin differentiation with Giemsa C-banding and fluorescent counterstaining inCephalanthera (Orchidaceae)

Abstract

Detailed studies of the chromosomes of the three Austrian species of the genusCephalanthera showed them all to have basically similar karyotypes. BothC. damasonium (2n = 36) andC. longifolia (2n = 32) have three large and several classes of smaller chromosome pairs. The karyotype ofC. rubra (2n = 44) is composed of four large and several groups of smaller pairs. The heterochromatin in these species amounts to about 10% of total karyotype length. All the chromosomes have Giemsa-positive centromeres, but only a few have intercalary or terminal bands. Using differential fluorescent staining with DAPI/actinomycin D, quinacrine/actinomycin D (both A-T specific), and chromomycin A3/distamycin A (G-C specific) three different types of major heterochromatic bands can be characterized in respect of their satellite DNA composition: highly A-T rich, slightly A-T rich, and very G-C rich. The chromosomes ofC. longifolia contain more A-T rich C-bands than those ofC. damasonium, while the latter's have more G-C rich heterochromatin. In both species several C-bands appear as secondary constrictions or gaps in the Feulgen-stained chromosomes, but most likely, in each species there is only one pair of chromosomes where the secondary constrictions function as nucleolus organizing regions. No major intraspecific variation could be observed except on one small chromosome pair ofC. longifolia which had a heteromorphic C-band in most individuals. Possible pathways of karyotype evolution involving polyploidy and Robertsonian events are discussed.