Abscisic acid, phaseic acid and gibberellin contents associated with dormancy and germination in barley

Analyses of abscisic acid (ABA), ent‐kaurenoids and gibberellins (GAs) showed that there were major changes in the contents of these compounds associated with germination of after‐ripened barley (Hordeum vulgare cv. Schooner and cv. Proctor) grain but not in hydrated dormant grain. Embryos from dormant and after‐ripened dry grain contained similar amounts of ABA, of ent‐kaurenoids and of GAs, determined by gas chromatography‐mass spectrometry‐selected ion monitoring. In embryos of after‐ripened grain, ABA content decreased rapidly after hydration and ABA appeared to be metabolized (inactivated) to phaseic acid (PA) rather than diffusing into the endosperm or the surrounding medium as previously thought. Similar changes in ABA occurred in hydrated dormant grain during germination in darkness. Accumulation of ent‐kaurenoids and GAs, including GA1, the first biologically active GA in the early 13‐hydroxylation biosynthetic pathway, occurred to a much greater extent in after‐ripened than in dormant grain and these changes occurred mainly after 18 h of hydration when ABA had already decreased and germination was occurring. The block in ent‐kaurenoid and GA synthesis in dormant grain appeared to occur prior to ent‐kaurene in the biosynthetic pathway. These results are consistent with the view that ABA is the primary effector of dormancy and that after‐ripening involves the development of the ability to reduce the amount of ABA quickly following hydration. Accumulation of GAs does not appear to be causally related to loss of dormancy but it does appear to be related to germination.