Release of dormancy in sunflower embryos by dry storage: involvement of gibberellins and abscisic acid

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Abstract
Excised Helianthus annuus L. embryos became dormant during the third week after anthesis. At this stage a short drying treatment (3 d) led to a slight improvement in germination but a 6-week dry storage caused a complete release from dormancy. The short drying treatment, however, elicited the embryos' response to an exogenous concentration of GAs which was unable to promote germination of fresh embryos. It therefore appeared that a short drying treatment changed the sensitivity to GAs but was not capable of directing embryo metabolism completely towards a germinative mode. Moreover, this drying treatment reduced considerably the ABA content in both the axis and the embryo. Nevertheless, no correlation could be established between germinability and the ABA content since the amount of ABA was not modified by the 6-week dry storage. The key step for predisposing the seeds to germinate is the suppression of the capacity for ABA synthesis in the axis, a suppression which takes place during 6-week dry storage.