Physiological Effects of Gibberellic Acid. X. The Release of Gibberellin-Like Substances by Germinating Barley Embryos

Barley embryos, completely free from endosperm, were excised from germinating grain at various times and allowed to diffuse into an aqueous medium for varying lengths of time. At the end of this time, the embryos and ambient solutions were separately extracted. Gibberellin-like activity in the extracts was determined with the barley endosperm bioassay using seed from the same variety, harvest and treatment schedule as was employed for the embryo diffusion experiments. Gibberellin-like substances were released by embryos throughout the 60 hour germination period, though at no time during this period could sufficient activity be extracted from the embryos themselves to account for the observed release. Solvent partitioning and chromatography identified at least one major acidic component migrating at an Rf similar to that of GA(3).It is concluded that the endogenous gibberellin-like substance(s) originates within the embryo during germination, and that the release of this substance(s) is temporally consistent with, and quantitatively sufficient to account for the in vivo endosperm mobilization response syndrome. A gibberellin-like substance is undoubtedly the endosperm mobilizing hormone.