Abscisic Acid and the Germination of Thermodormant Lettuce Fruits (Lactuca sativa cv. Grand Rapids). The Fate of Isotopically Labelled Abscisic Acid

Abstract

AbstractABA inhibits the germination of Grand Rapids lettuce seeds at a temperature at which photoblastism is not observed. This ABA inhibition can be overcome by GA, or cytokinin, or red light acting alone or in concert. At high levels of ABA the ameliorative effects of GA, cytokinin or red light are not manifest and it is suggested that lettuce seeds' response to a given level of ABA is temperature dependent, and any interaction which may be observed between ABA and other regulators, or red light, likewise is temperature dependent.Seeds only actively metabolize ABA after germination is complete though ABA does influence the germination process proper. Some radioactivity, originally applied as 14C ABA, cannot be extracted from 14C ABA treated seeds by methanol, and this “fixed” ABA can constitute more than 50% of the activity taken up by the seeds. High levels of “fixed” ABA are found in seeds which do not germinate. As well as this “fixed” ABA two labelled metabolites arise in seeds treated with 14C ABA. The levels of these rise in seed extracts as the level of extractable ABA decreases.Whilst ABA can affect germination our results do not allow us to assign a specific regulatory role to ABA in seed germination.