Changes in polyamines during bud dormancy in almond cultivars differing in their flowering date

Climate change may impact winter chill. Research on chilling models needs to be intensified, in order to prepare fruit growers for the agroclimatic changes that lie ahead. However, given substantial knowledge gaps in bud dormancy mechanisms, accurate models are still a long way off. This research documented the change in polyamines (PM) associated with seasonal bud dormancy in early flowering almond (Prunus amygdalus L.) cv. 'Moheb' and late flowering cv. 'Rabi'. The objective was to evaluate the change and possible role of PM during the endodormancy transition phase. The results show that chilling accumulation was first accompanied with a rise in putrescine (Put), spermidine (Spd), and spermine (Spm) concentrations. Therefore, low Put, Spd, and Spm levels, at the starting date of experiment, before receiving any natural chilling, may be associated with the imposition of bud dormancy. Regardless of cultivar, Spm was the most abundant free PA with a range of 11.3-19.0 nmol g(-1) F.w. for 'Moheb' and 22.1-29.7 nmol g(-1) F.w. for 'Rabi'. The continuously increases in Spm indicates that it may play an important played role in cold tolerance and flower bud development processes. Diamine oxidase (DAO) activity significantly decreased from December 2nd to February 24th (post-dormant stage) from 2.3 to 1.0 in 'Moheb' and from 1.8 to 0.7 U g(-1) (F.W.) (min-1) in 'Rabi'. Polyamine oxidase (PAO) activity showed a similar pattern, but the values of PAO activity were higher than the ones obtained for DAO activity. At the late stages, there was an inconsistent trend in differences in almond bud Put, Spd, and Spm among cultivars. Genotypic differences affecting the bloom time could account for the observed differences in the polyamine levels of the cultivars.