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Abstract
RNA and protein metabolism were greatly altered during aging, as well as after wounding and auxin treatment of aged pea epicotyls (Pisum sativum L. cv. Alaska). Aging was initiated by removal of the hooks and plumules from actively-growing plants. Lanolin was applied to the cut ends and the plants were allowed to age for up to four days. During this aging period several marked, degenerative events occurred. Ribosomal RNA and messenger RNA contents declined, polyribosomes disaggregated and the protein synthesizing capacity of the polysomes decreased. Two-dimensional, silver-stained protein patterns revealed that aging altered the relative amounts of specific cellular proteins accumulated in vivo. In addition, polypeptide patterns generated by cell-free translation of total and polysomal RNA, isolated from unaged and aged tissues, showed dramatic modifications.
Wounding treatment of aged pea epicotyls stimulated rapid polyribosome formation. Increases in RNA content and protein synthesizing capacity were the result of changes in transcription and translation, although translation was affected to a much greater extent. Minor differences were seen in the two-dimensional, silver-stained protein patterns for wounded tissue. Wounding caused changes in the messenger RNA populations as determined by two-dimensional gel electrophoresis of cell-free translation products which were substantially different from the control.
Auxin treatment of aged pea epicotyls increased the poly(adenylic acid) content of free and membrane-bound polyribosomes. The increased amount of messenger RNA in these polysomes was not the result of a shift of non-polysomal message into polysomes. The increase in poly(adenylic acid) content was exceeded by an increase in the protein synthesizing capacity of the polysomes. In contrast to wounding, auxin appeared to affect transcription to a greater extent than translation. Auxin caused only minor changes in two-dimensional, silver-stained protein maps, whereas extensive alterations were observed for polypeptides synthesized in vitro.
