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

Abstract

Recei-cd May 23, 1967. Sum,itmary. Barley embryos, completely free from endospernm, wvere excised from germinating grain at various times and al'lowed to diffuse into an aqueous medium for varying lengths of time. At the end of this time, the embrvos and ambient solutioins were separately extracted. Gibberellin-like activity in the extracts was determined with the barley endosperm bioassay using seed from the same varietv, hiarvest and treatment schedule as was employed for the emibryo diffusion experiments. Gibberellin-like sutb-stances were released by embryos thTroughout the 60 hour germination period, though at no time during this period could sufficient activity be extracted from the embryos themii-selves to account for the observed release. Solvent partitionling and chromatography identified at least one major acidic component migrating at an Rf similar to that of GA3. 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 con-sistent with, and quantitatively sufficient to account for the in vivo endosperm mobilization response synldroIiie. A gilbberellin-Fke substance is uindotlubtedly the endospernm iinI)ilizinlr hormiionie. In 1890 Brown and Morris (5) wrote, ". . we must assumle that the presence of the germl capable of development has some mysterious power of influ-encing the aleurone cells across the intermediate dead tissue of the starch-conitaininig portions of the endo-sperm, and of so far controlling these metabolic processes as to cause secretion of a special enzvme." Brown and Morris were commenting sceptically on an astute and foresighted report by Haberlandt (11) that the aleurone layer was the source of amvlolvtic enzvnyes during germination. I ronicallv, however, their statement quite adequately describes the results obtained some 70 vears later. In 1960 Yomo (36) and Paleg (22) independently demonstratedl that gibberellic acid (GA,) could