title: Naphthylphthalamic acid-binding sites in cultured cells from Nicotiana tabacum.
abstract: Naphthylphthalamic acid (NPA), an inhibitor of polar auxin transport, binds with high affinity to membrane preparations from callus and cell suspension cultures derived from Nicotiana tabacum (K d approx. 2·10(-9) M). The concentration of membrane-bound binding sites is higher in cell suspension than in callus cultures. The binding of NPA to these sites seems to be a simple process, in contrast to the binding of the synthetic auxin naphthylacetic acid (1-NAA) to membrane preparations from callus cultures, which is more complex (A.C. Maan et al., 1983, Planta 158, 10-15). Naphthylacetic acid, a number of structurally related compounds and the auxin-transport inhibitor triiodobenzoic acid were all able to compete with NPA for the same binding site with K d values ranging from 10(-6) to 10(-4) M. On the other hand, NPA was not able to displace detectable amounts of NAA from the NAA-binding site. A possible explantation is the existence of two different membrane-bound binding sites, one exclusively for auxins and one for NPA as well as auxins, that differ in concentration. The NPA-binding site is probably an auxin carrier.
authors.affiliation: Department of Plant Molecular Biology, Botanisch Laboratorium, Rijksuniversiteit, Nonnensteeg 3, NL-2311 VJ, Leiden, The Netherlands.
authors.forename: A C
authors.initials: AC
authors.lastname: Maan
authors.forename: B
authors.initials: B
authors.lastname: Kühnel
authors.forename: J J
authors.initials: JJ
authors.lastname: Beukers
authors.forename: K R
authors.initials: KR
authors.lastname: Libbenga