RIBONUCLEIC-ACID SYNTHESIS IN GERMINATING CASTOR BEAN ENDOSPERM

Total RNA extracted from castor bean endosperm at various stages during germination has been separated into three fractions: low molecular weight RNA (tRNA and 5S ribosomal RNA), ribosomal RNA (18S and 28S), and polyadenylated RNA. Although these fractions were readily detected in the endosperm of dry seeds, cellular content increased significantly during germination reaching a peak on the third or fourth day. (14C]Adenine and [3H]uridine have been used to label cellular. RNA, and the capacity of the tissue to incorporate these precursors established that the maximum rate of synthesis of all major RNA fractions occurred after 2 d growth. When homogenates obtained from [14C]adenine-labelled tissue were fractionated to yield crude nuclear and cytoplasmic preparations, the kinetics of radioactive labelling indicated that newly synthesized RNA appears firstly in the nucleus and subsequently in the cytoplasm.The present results suggest that synthesis of the proteins responsible for the metabolic activity of germinating endosperm tissue depends primarily on transcription during imbibition and germination rather than the activation of preformed RNA species already present in the dry seed. © 1979 Oxford University Press.