Uptake of [2-14C]abscisic acid and distribution of 14C in apple embryos

Pyrus malus L. var. Golden delicious embryos were incubated with (±)-[2-¹⁴C]abscisic acid (ABA) (10^-5 M, 355 kBq mol^-1). After incubations of various durations, the radioactivity was measured in whole embryos, cotyledons, and embryonic axes.With either 48-h or 16-d incubation periods, the uptake of [¹⁴C]ABA depended upon the mode of culture used. The lowest values corresponded to the absorption by the embryonic axis, the highest to the absorption by the distal parts of the two cotyledons. The cotyledons accumulated the main part of the radioactivity under all conditions. Dormant and almost completely after-ripened embryos cultivated for 4 d showed no significant differences in the radioactivity uptake for identical modes of culture. There was a linear relationship between exogenous ABA concentrations (0.5 to 3.10^-5 M) and ABA uptake for embryos cultivated for 4 d with the distal parts of the cotyledons immersed in the medium.Abbreviations ABA abscisic acid. RM, RM⁺, C/2 M, and CM are different modes of embryo cultures: embryonic axis immersed alone (RM), together with the proximal parts of the cotyledons (RM⁺); distal parts of the cotyledons immersed alone (CM); embroyo flat on the medium, the root and the external surface of one cotyledon being in contact with the medium (C/2 M) - PP proximal parts of the cotyledons - DP distal parts of the cotyledons