A comparison of the activation of ribosomal RNA synthesis during germination of isolated and non-isolated embryos of Triticum aestivum L.

Incorporation of [¹⁴C]uridine into ribosomal RNA and ribosomal RNA precursor fractions was studied in isolated wheat embryos and in embryos remaining within the intact grains during germination. In isolated embryos, radioactive 25S and 18S as well as 31S RNA species appeared already within the first 3 h of germination. In non-isolated embryos, radioactivity could be detected in the mature ribosomal and pre-ribosomal RNA fractions only after 6 h and 12 h germination, respectively. It is concluded that transcription of ribosomal sequences is activated almost immediately in isolated wheat embryos but remains repressed for several hours when the embryo germinates under natural physiological conditions.