Antibodies against distinct ABP1 regions modify auxin binding to ABP1 and change the physiological auxin response of maize coleoptile cections

Twelve peptides spanning the whole maize ABP1 sequence were synthesized and coupled to sepharose. Peptide — specific antibodies were purified from and ABP1 IgGs on peptide affinity columns, and binding of NAA to purified ABP1 in the presence of the IgGs was assayed. Of all the antibodies tested, only three increased the KDof auxin binding. Correspondingly, auxin-caused pH shift of the incubation medium by coleoptile sections was strongly influenced by these three antibodies. In addition, antibodies directed against the peptides corresponding to the N- and the C-terminus were also able to reduce the auxin-induced pH drop.