Changes in hormone concentrations during dormancy release of oil palm (Elaeis guineensis) seeds

Oil palm (Elaeis guineensis) seeds are highly dormant immediately after harvest. In practical horticulture this dormancy has been traditionally overcome by a dry-heat treatment and, more recently, through the application of hydrogen cyanamide (HC). Initiation and release of dormancy have been related in other plant species to changes in endogenous hormone concentrations. Therefore, the effect of the aforementioned dormancy release treatments on germination and on endogenous concentration of indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellins GA₁, GA₃ and GA₂₀ (GAs), zeatin/zeatin riboside and N⁶ (Δ²-isopentenyl) adenine/N⁶ (Δ²-isopentenyl) adenosine was evaluated in oil palm seeds. Heat- and HC-treated seeds germinated above 90% after 37 d, while germination of control seeds was below 4% at the same time. A sharp reduction in ABA concentration in embryos and endosperm was the most notable outcome during the dry-heat and HC treatments, the latter one in a lesser degree. HC treatment additionally caused an increase in IAA levels in embryos and endosperm during the imbibition phase. Changes in concentration of other hormones (e.g., GAs and cytokinins) could not be directly related to dormancy release in this species. Participation of additional factors, such as changes in sensitivity to plant hormones, cannot be ruled out.