Wheat embryo ribonucleates. VI. Comparison of the 3′-hydroxyl termini in 'rapidly labelled' RNA from metabolizing wheat embryos with the corresponding termini in ribosomal RNA from differentiating embryos of wheat, barley, corn and pea

Abstract

The NaCl-insoluble (2.5 M, 0.degree. C) fraction of wheat embryo RNA (iRNA) can be labeled when wheat embryos are subjected to either short-term (0.5 h) or long-term (24 h) imbibition in a medium that contains tritium-labeled adenosine, guanosine, cytidine and uridine. Electrophoretic analyses reveal that, after short-term labeling, there is a broadly heterodisperse distribution of radioactivity in ''rapidly labeled'' i[3H]RNA, but after long-term labeling, there is an essentially trimodal distribution of radioactivity in i[3H]RNA, but after long-term labeling, there is an essentially trimodal distribution of radioactivity in i[3H]RNA. End-group analyses reveal that, after short-term labeling, adenosine is the principal 3''-hydroxyl terminus in all centrifugal subfractions of ''rapidly labeled'' i[3H]RNA, whereas cytidine (in 5.8S rRNA), guanosine (in 18S rRNA) and uridine (in 26S rRNA) are the principal 3''-hydroxyl termini in centrifugal subfractions of wheat embryo i[3H]RNA. Guanosine is also the principal 3''-hydroxyl terminus in the 18S rRNA of differentiating embryos excised from both monocotyledonous (wheat, barley, corn) and dicotyledonous (pea) seedlings. The implications that the end-group measurements may have for current views about the possible biochemical involvements of 3''-hydroxyl terminal sequences in both mRNA and 18S rRNA are subjects of discussion. Incidental to the principal investigation, an existing technique for analyzing the RNA contents of cellular materials was appropriately modified to circumvent interference from UV-absorbing pigments, which, when present, prevent application of the method to plant materials.