Affinity labels for auxin binding sites in corn coleoptile membranes

Area of Science:

• Plant biology
• Molecular biology
• Biochemistry

Background:

• Auxin is a key plant hormone regulating growth and development.
• Understanding auxin binding sites is crucial for deciphering its molecular mechanisms.
• Zea mays coleoptile membranes provide a model system for studying auxin perception.

Purpose of the Study:

• To identify and characterize amino acid residues involved in auxin binding sites.
• To utilize affinity labeling techniques to probe the auxin binding pocket.
• To investigate the chemical nature of the auxin binding site in Zea mays.

Main Methods:

• Affinity labeling of Zea mays coleoptile membranes using two auxin analogues: CAPA and Diazo-Chloramben.
• Assessing the effect of labeling on the subsequent binding of 1-naphthylacetic acid (NAA).
• Employing sulphydryl reagents like p-mercuribenzoate (PMB) to probe for reactive residues.

Main Results:

• The diazonium salt of CAPA (2-chloro-4-aminophenoxyacetic acid) inhibited NAA binding at pH 8-9.
• Diazo-Chloramben (2,5-dichloro-3-aminobenzoic acid) also inhibited NAA binding capacity across a pH range of 6-9.
• p-mercuribenzoate (PMB) strongly inhibited auxin binding activity.
• NAA pre-treatment protected binding sites against Diazo-Chloramben and PMB at pH 6.

Conclusions:

• Specific amino acid residues within the auxin binding site environment have been tentatively identified.
• The results suggest the involvement of both amino and sulphydryl groups in auxin binding.
• Affinity labeling provides insights into the molecular structure of auxin receptors.