Observations on rRNA gene replication in Chara vulgaris evaluated by in situ [3H] rRNA-DNA hybridization

Abstract

ABSTRACT In situ [3H]rRNA-DNA hybridization showed that: (1) during the cell cycle in antheridial filaments of Chara vulgaris the rDNA gene content doubles during a 2h period in mid-S-phase, which corresponds to about 13% of the duration of this phase; (2) doubling of the number of grains occurs during mid-S-phase irrespective of the developmental stage of the antheridial filaments; (3) the numbers of autoradiographic grains in comparable phases of successive cell cycles preceding spermatid formation are the same. Thus the gradual reduction of total nucleolar volume (estimated per nucleus) occurring in successive cell cycles preceding spermatid formation is not associated with a decrease in the number of rDNA genes.