Abstract: By using the micro-volume radio-ligand binding essay (MRLB), the changes in the kinetic characteristics of the ABA binding protein (s) of the Kyoho grapevine (V/t/s vinifera × V. labrusca) fruits during the different stages of fruit development have been studied. The changes in the berry volume growth, concentration of sugar, organic acids and ABA in fruit mesocarp have been determined especially for the studies of ABA-binding protein. The dissociation constant (Kd) and ABA-binding maximum volumes (Bronx)were determined by the Scatchard plots for the ABA-binding protein (s) in microsomes of the fruits. They were: Kd =17.5, 50. 0, 6.3, 13.3 nmol/L: Bmax=98.6, 523.0, 41.6, 85. 4 pmol/g protein respectively for the fruit developmental phase Ⅰ , Ⅱ, veraison and phase Ⅲ. The Scatchard plots showed a rectilinear function for all of the developmental phases including veraison, which suggests in the fruit microsomes at the same developmental phase, the existence of either one kind of the same or several different kinds of ABA-binding sites of identical or similar kinetic characteristics and of high affinity. In different developmental stages, however, changes of the protein at the ABA-binding sites might occur. The binding affinity of ABA-binding protein (s) for ABA was showed to be higher at veraison stage than in other developmental phases and this binding affinity increased nearly by 10 times from the phase Ⅱ to veraison, whereas the concentration (Bmax) of the ABA-binding protein (s) decreased to the minimum at veraison. The reason why such low concentration of ABA at veraison is capable to trigger the onset of fruit ripening might be due to the increase of the affinity of ABA-binding protein (s) for ABA at this time. The possible functions of the ABA-binding protein (s) for fruit development during the different developmental stages were discussed, and it is suggested that the protein (s) detected could be the putative receptor (s) or carrier (s) for the action of this plant hormone in grapevine.

Key words: Grapevine, Fruit, ABA, ABA-binding protein, Affinity