Number, size, and transcriptional activity of nucleoli during different periods of interphase in antheridial filaments of Chara vulgaris L.

In antheridial filaments of Chara vulgaris the number of nucleoli within a single cell nucleus ranges from 3 to 12. The sizes of nucleoli vary from 0.2 to 3.5 micron in diameter. Mean number of micronucleoli, i.e. the smallest nucleoli of 0.2-0.5 micron in diameter which are distinguished after silver staining is higher than that estimated with the use of toluidine blue method according to Smetana et al. [34], the latter procedure resulting in a less contrasting visualization. Throughout the course of the whole period of interphase the mean number of nucleoli was found unchanged in successive phases and it equals some 6.5 per nucleus. Concurrently, the total volume of nucleoli increases progressively reaching maximum value by the end of the G2 phase which is attributed to the increase in number of largest nucleoli. On the basis of the analysis of 3H uridine incorporation and an in situ determination of RNA polymerase activity using the method adopted by Moore and Ringertz [25] it was evidenced that the mean transcriptional activity of nucleoli larger than 0.5 micron in diameter is not dependent upon nucleolar number within a single nucleus. It is concluded that the diverse appearance of nucleoli in cells being located precisely at the same stage of interphase reflects temporal changes of their sizes consisting in an asynchronous pulsation of individual nucleoli.