Ribonucleic Acid and Protein Metabolism in Pea Epicotyls

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Abstract
Applications of auxin to the tips of intact aged pea epicotyls resulted in an increase in the content of polyribosomes and poly(A) and in the capacity of isolated polysomes to support protein synthesis in vitro. Few changes were seen in the 2-dimensional gel patterns of silver-stained proteins accumulated (or degraded) in vivo even after 15 h of auxin treatment. In contrast, substantial changes were evident in the 2-dimensional gel fluorographs of polypeptides generated in vitro by total RNA and by polysomal RNA from tissue treated with auxin for only 6 h. Of the 200 spots resolved by fluorography, total RNA from auxin-treated tissue generated 33 spots with increased intensity and 10 with decreased intensity; polysomal RNA yielded 33 spots which increased and only three that decreased. In general, the polypeptides that increased in intensity were higher molecular weight and those that decreased were lower molecular weight. These changes occurred prior to growth and might be prerequisite for the auxin-induced slow growth response seen in this aged tissue. Comparisons were made between the changes in RNA and protein metabolism occurring during aging and after wounding and auxin treatment of aged tissue. Aging causes a decline in poly(A), polysomes, and protein synthesizing capacity, whereas wounding and auxin treatment cause increases. Wounding appears to act primarily at the level of translation, whereas auxin has a greater effect on transcription. The use of excised tissue to study auxin effects on RNA and protein metabolism should be avoided.