Abscisic Acid in Different Parts of the Developing Soybean Fruit

Summary The endogenous levels of abscisic acid (ABA) were studied in pericarp (vascular bundles and remaining part) and seed parts (hilum, testa, cotyledons, embryo axis) of the soybean fruit at 4 different stages of development. In seeds, highest concentrations of ABA were determined within the testa during intensive growth, and lowest amounts occurred within the hilum. In the pericarp, the ABA levels were much lower than in the seed at all stages investigated. The ABA concentration in the ventral vascular bundles exceeded that of the remaining pericarp at early stages; afterwards an inverse proportion occurred. The dynamics of ABA changes in the vascular bundles of the pericarp resembled those occurring in the seed parts but differed significantly from the remaining pericarp. In the pericarp, ABA seems to be involved in senescence control, and in the seed in phloem unloading. Concerning the whole fruit, an increasing concentration gradient of ABA along the vascular assimilate translocation path up to the testa was found indicating a physiological role of ABA in the process of assimilate translocation.