Abscisic acid content of a nondormant sunflower (Helianthus annuus L.) mutant

A sunflower (Helianthus annuus L.) mutant was observed in the progeny of a cross between the sunflower cultivar HA 89 and an amphiploid of a H. divaricatus L. × P21 cross that exhibited loss of dormancy induction in the developing embryo. Seeds of this mutant frequently germinate on the head about 40 d after pollination (DAP). In contrast to other nondormant sunflower mutants reported previously, the cotyledons of this mutant remain green, whereas other nondormant mutants exhibit loss of pigmentation. The objective of this investigation was to compare the level of abscisic acid, a plant hormone that induces dormancy in developing embryos, in the nondormant green mutant (ndg) and HA 89 from which ndg was derived. Immunoassays showed that abscisic acid was present in ndg and the levels decreased from a maximum at 5 to 20 DAP to basal levels at 25 DAP. The levels of abscisic acid were not significantly different from those in the control plant HA 89. We conclude that the nondormancy trait is due to a mutation that renders ndg insensitive to abscisic acid.