In-vitro Auxin Binding to Particulate Cell Fractions from Corn Coleoptiles

• Published in: Planta Vol. 107; no. 4; pp. 325 - 340
• Main Authors: Hertel, R., Thomson, K.-St, Russo, V. E. A.
• Format: Journal Article
• Language: English
• Published: Germany Springer-Verlag 01-01-1972
• Subjects: Auxins; Binding sites; Cell membranes; Centrifugation; Coleoptiles; Corn; Kinetics; Liver; Particulate matter; Receptors
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/bf00386394

When low concentrations (e.g. 10-6 M) of labelled 3-indoleacetic acid (14C-IAA) or α-naphthaleneacetic acid (14C-NAA) are added in vitro to homogenates of corn coleoptiles, radioactivity is reversibly bound to pelletable particles. From the saturation kinetics of the binding it is possible to estimate an apparent KM between 10-6 M and 10-5 M and a concentration of specific sites of 10-7—10-6 M per tissue volume. The binding is auxin-specific. Among many compounds tested, only auxins and such auxin analogues that are known to interact directly with auxin in transport and/or growth were found to interfere with this binding. For instance, the growth-active D-dichlorophenoxyisopropionic acid at 10-4 M inhibits 14C-NAA binding more than the less active L-isomer. The auxin-binding fractions are practically free of DNA and cytochrome-C oxidase and contain binding sites for 1-naphthylphthalamic acid. The results are discussed in context with the hyothesis—derived mainly from physiological data—that auxin receptors are localized at the plasma membrane.