Elucidation of the molecular mechanisms behind breaking flower bud dormancy in cherry trees with special focus on the role of hydrogen cyanide

Dormancy is the ability of some species, i.e. perennial woody plants in the Prunus genus, to suspend and resume growth in response to seasonal changes. In order to re-start growth flower buds need a certain amount of chill units in winter and subsequent heat hours in spring. Especially in warmer production areas and now increasingly due to global warming, the chilling requirements cannot be completely fulfilled. Therefore, different cyanide-based chemicals have been used to fully achieve the required chill units, and also to synchronize flowering time, which increases the fruit yield and facilitates fruit harvesting. The best chemical used to date is Dormex® (AlzChem), which can bring forward flowering time around one week compared to untreated controls. However, the EU has banned this chemical in 2008 due to concerns towards environmental effects and operator exposure. The molecular mechanisms by which cyanamide, the principal component of Dormex®, brings forward flowering time is still unknown. Some studies suggest that cyanamide acts through the release of hydrogen cyanide. Hydrogen cyanide can also be produced by the hydrolysis of cyanogenic glucosides present in Prunus. Furthermore, it is known to inhibit the antioxidant enzymes catalase and superoxide dismutase. We propose that the consequently increased ROS levels activate certain ‘breaking dormancy’ genes. To prove this, we have treated dormant cherry flower buds with Dormex® to analyze the effects on the transcript, protein and metabolite level. Finally, we will also detect the cyanogenic glucosides in cherry flower buds and in different parts of the fully developed flower.