Changes in endogenous ABA levels in developing somatic embryos of Norway spruce (Picea abies (L) Karst) in relation to maturation medium, desiccation and germination

An embryogenic suspension culture of Norway spruce (Picea abies (L.) Karst.) was matured with three combinations of abscisic acid (ABA) and polyethylene glycol 4000 (PEG): (1) 40 mu M ABA without PEG; (2) 40 mu M ABA + 5% PEG or (3) 15 mu M ABA + 5% PEG. The endogenous content of ABA in the embryos was shown to be dependent on the exogenous concentration of ABA and on the osmotic potential of the medium. Low osmotic potential of the maturation medium due to inclusion of PEG increased the maturation frequency but affected germination of the embryos negatively. The low germination frequency of PEG treated embryos was related to morphological traits as small size and intercellular spaces below the apical meristem. These abnormalities may be caused by the osmotic stress induced by PEG, Partial drying was a prerequisite to obtaining germination of mature embryos. The increased germination after partial drying was attributed to a substantial decrease in endogenous levels of ABA and one effect of partial drying may be the breakdown of endogenous ABA. (C) 1997 Elsevier Science Ireland Ltd.