Abstract: The different subeellular fractions of apple ( Malus pumila Mill) fruit were separated with differential centrifugation, and the distribution of ABA-binding activities in the subcellular fractions was determined. Both the in vivo and in vitro ABA binding assayed indicated that the ABA binding sites which were detectable only in the subcellular fractions obtained from the fruit tissues fed with 3H-ABA, were situated in the soluble fractions of the fruit cells. These sites could form a stable complex with ABA. The lucifer yellow CH linked ABA (ABA- LYCH) which was shown to inhibit the germination of red amaranth (Amaranthus tricolor L. ) seeds as effectively as ABA, also inhibited the in vivo ABA binding in tissues of apple fruit. ABA-LYCH could specifically stain the out sphere of the cells in tissue or that of the macerated cells of unripe apple fruit. With the presence of BSA, the ABA-linkage complex could be transported into the cells across the plasma membrane and intensively aggregated in the places of cell contact. The results suggest that there exists a carrier of ABA localized on plasmalemma, which transports ABA across the plasma membranes before the ABA is bound at the ABA-binding sites situated in the cytoplasm.

Key words: Fruit of Malus pumila, ABA, ABA binding sites, Subcellular localization, ABA fluorescent Probe