Since, the critical temperatures affecting the bud and the associated damage are variable and unknown for most of the local almond cultivars, one of the aims of this study was to identify the critical temperatures of almonds buds at different development stages. Three almond cultivars including ?Moheb? (early flowering), ?Mamaie? (medium-flowering) and ?Rabi? (Late flowering) were tested during the late winter to early spring seasons of 2018 and 2019. The results showed that the highest resistance to low temperature was observed in ?Rabi? in 2018 and in ?Mamaie? in 2019. ?Moheb? with the lowest resistance had the highest ion leakage in both years. The results also showed that with the advancement of the phenological stage of flower buds, the frost resistance decreased in all cultivars and the value of the lethal temperature changes depending on the year, cultivar and bud development stage. The study tested the effect of artificial chilling on the depth of endodormancy and the percentage of flower and vegetative budbreak, using the excised shoot method, in selected above almond cultivars. According to the results, the cultivars showed a narrow range of both chill and heat requirements (growing degree hours, GDH) for acceptable levels of flower budbreak, i.e. Moheb’ (250 h and 2132 GDH), ‘Mamaie’ (500 h and 2460 GDH) and ‘Rabi’ (500 h and 2624 GDH). In general, maximum budbreak was reached with less chilling accumulation in flower buds compared with vegetative buds. Excessive chilling caused a reduction of the heat requirements in flower and vegetative buds. By studying the biochemical changes in flower buds and their relationship with the mean time to budbreak, we conclude that the response of enzymatic and non-enzymatic antioxidant system was different in almond cultivars during different years. Although, the synthesis of osmotic compounds such as proline, total carbohydrates, sucrose, fructose and glucose increased with chilling in all studied cultivars, ?Moheb? had the lowest accumulation of these compounds during the dormancy and release of dormancy. At the starting date of experiment, before receiving any natural chilling, the concentration of polyamines was low in the buds. At the late stages, there was an inconsistent trend in differences in almond bud putrescine, spermidine, and spermine among cultivars. The highest activities of the catabolic enzymes of polyamines found at earlier stages of dormancy. By examining the level of damage in freezing stress conditions through measuring the water and total carbohydrate content in the shoots and flower buds, we observed that the degree of freezing tolerance in the shoot and flower buds of ?Mamaie? was highly dependent on the total carbohydrates and high concentrations of total soluble carbohydrates and low water content, respectively. In ?Moheb? and ?Rabi?, shoot and flower bud hardiness was related to the high concentrations of total soluble carbohydrates and water content. The results indicated that freezing resistance/susceptibility is cultivar dependent in almonds. Transcriptome analysis for the identification of genes responsible for bud burst time in almond cultivars that have different bud break time revealed that as the shoots were chilled, the expression levels of CBF1 and CBF2 in ?Moheb? steadily increased and reached its maximum at budbreak. The expression of CBF1 and CBF2 in ?Rabi? and ?Mamaie? initially increased with chilling accumulation at the beginning of dormancy, then remained at its maximum level, and gradually decreased at budbreak. Regardless of cultivar, MADS1 and MADS3 transcription factors were detected in the final stage of bud dormancy. This suggested that MADS1 and MADS3 could be interesting markers for the final stage of floral development. The results provided evidence that the synthesis of proline and sugars was coordinately regulated, where CBF had a key role. In this study, we studied the effect of putrescine application on the bud-break time of flower buds of ?Moheb? and ?Mamaie?. The results showed that putrescine has a positive effect on delaying flowering time. Key Words Flowering date, Critical temperatures, Cold signals, Chilling and heat requirements, Freezing.