The Kinetics of Inhibition of Auxin-Induced Growth in Green Pea Stem Segments by Actinomycin D and Other Substances

Inhibitors of nucleic acid and protein synthesis were applied to excised green pea stem sections in the absence and presence of IAA and the effects on growth noted as a function of time. Actinomycin D, which inhibits de novo RNA synthesis, ribonuclease, which degrades RNA, and puromycin, which prevents transfer of aminoacyl residues into the growing polypeptide chain, inhibit section growth only after lengthy lag periods of, respectively, 2, 8 and 5 hr. For actinomycin D and ribonuclease, preincubation in the inhibitor alone, prior to IAA application, does not reduce the lag period, indicating that the lag is not caused by slow penetration of the inhibitor. By contrast, chloramphenicol, which prevents binding of messenger RNA to ribosomes, and p-fluorophenylalanine, a competitive antagonist of phenylalanine, produce significant inhibitions in the first hour. The implications of these results for the mechanism of auxin action are considered.