ABSTRACT Freezing stress can be induced by spring late frost during the juvenile fruit stage in apricot ( Prunus armeniaca L.). Elucidating the molecular mechanisms by comparing the responses of different cold-tolerant varieties is essential for enhancing fruit quality and yield. Here, the juvenile fruits of Youyi (a cold-tolerant cultivar) and Longwangmao (a cold-sensitive cultivar) were exposed to either 24 ℃ or -2 ℃ for 5 hours. We found that the cold-tolerant cultivar displayed an enhanced antioxidant system and was protected from the cold damage observed in Longwangmao, including water-soaking, plasmolysis, and swelling of plastid thylakoids and mitochondrial cristae. Metabolomic and transcriptomic profiling revealed that freezing stress induced higher accumulation of chlorogenic acid, sinapyl alcohol, γ-aminobutyric acid, and polyamines in Youyi than in Longwangmao. Concurrently, the expression of key enzyme genes, i.e., shikimate O - hydroxycinnamoyl transferase ( HCT ), cinnamyl alcohol dehydrogenase ( CAD ), glutamic acid decarboxylase ( GAD ) and spermine synthase ( SPMS ), involved in phenylpropanoid and amino acid metabolism, was upregulated in Youyi under freezing stress. In addition, 45 transcription factors with differential expression were identified, such as ERFs , WRKYs , and HSFs , which probably modulated the freezing tolerance. These results suggest that the differential freezing tolerance between Youyi and Longwangmao cultivars is related to contrasting physiological responses to freezing stress, and the underlying transcriptomic and metabolomic regulatory networks are critical for juvenile fruits in acclimation to low temperature.
Yu et al. (Mon,) studied this question.