Surveying the Hormonome of Hazelnut Catkins During Winter Dormancy

Abstract

Deciduous woody perennials, such as hazelnut, undergo winter dormancy to protect sensitive tissues, such as flowers, from harsh conditions. The reproductive success of the tree is dependent on the release of dormancy under favorable conditions. To bloom, the tree must first experience a certain amount of chilling, followed by a certain amount of warmth. With global warming, many trees risk not being able to accumulate enough chilling to release dormancy. Also, when trees accustomed to warm climates are brought into cold climates, they might bloom prematurely and risk freezing damage. The latter is the case for hazelnut, recently adopted as a crop in Ontario, Canada. The present study investigates the hormonal regulation of dormancy in hazelnuts’ male flowers (catkins) by generating hormone profiles in early and late-blooming accessions throughout the dormant season. Abscisic acid (ABA), gibberellin (GA), auxin, cytokinin (CTK), their metabolites, as well as the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), were measured. ABA decreased with dormancy progression, while GA increased. This correlation implies ABA is primarily responsible for dormancy maintenance in catkins and GA works antagonistically to ABA. Indeed, the ABA/GA ratio steadily decreased throughout dormancy. For the first time, CTKs have been reported to steadily increase during dormancy, implying CTKs also have an antagonistic relationship with ABA. Auxin and ethylene appear to primarily play a role in the onset of dormancy. Interestingly, early blooming accessions failed to accumulate the auxin conjugate, IAA-Asp and had higher ACC levels throughout most of dormancy. Cumulatively, the present study has generated the most comprehensive hormone profile in dormant flowers of deciduous woody perennials and has identified potential strategies for the delay of bloom in hazelnut catkins through the manipulation of hormones.