Action of Inhibitors of RNA and Protein Synthesis on Cell Enlargement

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Abstract
Further studies with inhibitors of protein and RNA synthesis support the conclusion, drawn from work with chloramphenicol, that protein synthesis is a critical limiting factor in auxin-induced cell enlargement. The indoleacetic acid (IAA)-induced elongation of oat coleoptile sections was strongly inhibited by DL-P-fluorophenylalanine, and this was antagonized by phenylalanine. Puromycin at 10-4 M very strongly inhibited IAA-induced growth of oat coleoptile and artichoke tuber sections, and less actively that of pea stem sections. As with chloramphenicol, concentrations of puromycin which inhibited the growth of coleoptile sections had quantitatively similar effects on protein synthesis, as measured by the incorporation of c14-leucine into protein of coleoptile tissue. Actinomycin D actively inhibited both elongation and the incorporation of C14-leucine into protein in oat coleoptile sections, inhibition of the 2 processes going closely parallel. Of the analogues of RNA bases tested, 8-azaguanine strongly inhibited growth of artichoke tuber disks, but only 6-azauracil inhibited growth of oat coleoptile or pea stem sections. Compounds inhibiting growth generally inhibited the uptake of leucine as well. Thus auxin apparently causes plant cell enlargement by inducing synthesis of a messenger RNA and of new but unstable enzymes.