Abstract: A specific NPA N-l-naphthylpathalamic acid) -binding site with high affinity was found in the membrane component of Acer pseudoplatanus L. suspension culture cells. The dissociation constant (Kd) of NPA was approximately 7.5× 10-9mol/L. NPA binding was maximal after 60 min of incubation at 4℃. Synthetic auxin I-NAA, 2-NAA, 2,4-D and auxin transport inhibitor 2,3,5-TIBA were all able to compete with NPA for the binding. Site with Kd values ranging from 10-6 to 10-4 mol/L. These binding sites could be involved in the regulation of intracellular IAA level, thereby affecting cell growth.

Key words: NPA-binding site, Acer pseudoplatanus L., Auxin