The role of abscisic acid in the mechanisms underlying dormancy of yellow-cedar (Chamaecyparis nootkatensis) seeds

The effectiveness of different chemical treatments in replacing warm stratification and in reducing the requirement for cold stratification (moist chilling) was investigated. Treatments comprised of gibberellic acid (GA3) in combination with osmotic priming (using polyethylene glycol) or with other hormones (gibberellin₄₊₇ and benzylaminopurine) had a promotive effect on subsequent germination of whole seeds of yellow-cedar after a 60-day moist chilling period. Whole seeds exposed to GA₃ and to fluridone (the latter to diminish endogenous abscisic acid, ABA), exhibited increased germination with an increasing time of exposure to fluridone, even in the complete absence of moist chilling. A chemical treatment using the anaesthetic 1-propanol coed with a three day warm water soak (30°C), a two day GA ₃ treatment and 60 days of moist chilling not only promoted high germinability of yellow-cedar seeds, but also elicited vigorous post-germinative growth following seedling emergence under nursery greenhouse conditions and after establishment in natural stands.; Within the embryos of yellow-cedar seeds (but not the megagametophyte), ABA levels decreased with increasing time of exposure to a dormancy-breaking treatment; this process was also accompanied by a 10-fold lowered sensitivity of the embryo to S-(+)-ABA. Embryos that were fed S-(+)-[3H]-ABA (regardless of whole seed pretreatment, i.e. dormancy-breaking or control) metabolized the ABA to phaseic acid and dihydrophaseic acid.; A role for the VP1/ABI3 gene product as a regulator of dormancy was investigated In previous work, a gene homologue of the ABI3 gene of Arabidopsis was cloned from yellow-cedar (CnABI3). CnABI3 gene transcripts were present in developing seeds and in mature dormant seeds. ABA in combination with CnABI3 had a synergistic effect on Em-driven GUS expression when embryos were co-bombarded with Em-GUS and the CnABI3 gene driven by a constitutive promoter. Thus, the CnABI3 protein of yellow-cedar has similar functions to ABI3-like proteins of angiosperms. (Abstract shortened by UMI.)...