Distribution of 18S rRNA and rbcS mRNA in different A. acetabulum cell fragments: evaluation by semiquantitative RT-PCR analysis. Young cells of 20 to 30 mm in length without caps (A) and adult cells of 40 to 50 mm in length with nearly full-sized caps (B) were cut into four fragments corresponding to apical stalk fragment (A), middle stalk fragment (M), basal stalk fragment (B), and rhizoidal fragment (R). Equal amounts of total RNA, isolated from these cell fragments, were used as templates in RT-PCR with appropriate specific primers (see “Materials and Methods”). Left panel, Separation of RT-PCR products by agarose gel electrophoresis. The 850-bp piece corresponds to 18S rRNA and the 250-bp piece to rbcS mRNA. (L) indicates a DNA size ladder. Right panel, Densitometric record of the individual signals after blotting and hybridization with fluorescein-labeled A. acetabulum cDNA probes, expressed as relative units (RU).