Hormonal Profile in Vegetative and Floral Buds of Azalea: Levels of Polyamines, Gibberellins, and Cytokinins

The floral transition includes a complex system of factors that interact and involve various biochemical signals, including plant growth regulators. The physiological signals involved in the control of the floral transition have been sparsely studied and mainly in plant species whose genetics are poorly known. In this work, the role of polyamines, gibberellins, and cytokinins was investigated by analyzing their endogenous content in vegetative and floral buds of azalea. The results showed that there is a clear distinction between floral and vegetative buds with respect to the levels of these plant hormones, with floral buds containing higher amounts of conjugated polyamines, gibberellins (GAs) from the non-13-hydroxylation pathway (GA(9), GA(7), and GA(4)), and cytokinins (particularly isopentenyl-type species), and vegetative buds containing higher amounts of free polyamines and gibberellins from the early 13-hydroxylation pathway and fewer cytokinins. In conclusion, there is a specific pattern of endogenous hormone profiles in both vegetative and floral bud development in azalea, which may be relevant for future research on the control of flowering by exogenous hormone applications.