Abstract: A specific ABA-binding site with high affinity was found on the membrane parts of rice seedlings. The dissociation constant (Kd) for ABA was approximately 2.66×10-7 mol/L, the total concentration of the sites was 4 nmol mg-1 protein, and the ABA-binding was maximal at pH 4.5. The activity of specific ABA-binding sites was 115% higher at 0℃ than at 25℃. ABA-binding was increased with time, reaching maximal in lb, and then decreased gradually. The decrease of ABA-binding may be resulted from the neutralization of the sites. The studies suggested that specific ABA-binding sites with high affinity was the carrier of ABA or, more probably, the receptor of ABA.

Key words: ABA, Rice, ABA-Binding, Membrane-Bound protein, Specific ABA sites