Ribosomal DNA in different members of a family of green algae (Chlorophyta, Dasycladaceae): an electron microscopisal study.

Active cistrons and non-transcribed spacers of rDNA were made visible in spread preparations of nucleolar material from different species of the green alga family Dasycladaceae (Chlorophyta). The data observed show a difference in length in transcribed rDNA regions between Acetabularia peniculus Solms-Laubach, Acetabularia dentata Solms-Laubach on the one hand and Acetabularia ryukyuensis Okamura et Yamada, Dasycladus clavaeformis J. Agardh, Cymopolia van bosseae Solms-Laubach and Batophora oerstedii J. Agardh on the other: The large size difference between spacer intercepts of different species is very conspicuous. While the Acetabularia species have long non-transcribed spacers they are very short or even not observable in the other Dasycladaceen species studied. Peculiarities found in rDNA include extra long spacers between cistrons, single extra long cistrons together with rDNA cistrons on the same strand and rDNA-sized cistrons alternately arranged on one strand with larger sized cistrons. In spite of extensive searching, inversions were never found in spread nucleolar material. However, they were frequent in spread material of whole nuclei.