Abstract
Cold storage (CS) can induce a physiological disorder known as chilling injury (CI) in nectarine fruits. The main symptom is mealiness that is perceived as non-juicy fruit by consumers. Postharvest treatments such as controlled atmosphere (CA; a high CO2 concentration and low O2) have been used under cold conditions to avoid this disorder. With the objective of exploring the mechanisms involved in the CA effect on mealiness prevention, we analyzed transcriptomic changes under six conditions of “Red Pearl” nectarines by RNA-Seq. Our analysis included just harvested nectarines, juicy non-stored fruits, fruits affected for CI after CS and fruits stored in a combination of CA plus CS without CI phenotype. Nectarines stored in cold conditions combined with CA treatment resulted in less mealiness; we obtained 21.6% of juice content compared with just CS fruits (7.7%; mealy flesh). RNA-Seq data analyses were carried out to study the gene expression for different conditions assayed. During ripening, we detected that nectarines exposed to CA treatment expressed a similar number of genes compared with fruits that were not exposed to cold conditions. Firm fruits have more differentially expressed genes than soft fruits, which suggest that most important changes occur during CS. On the other hand, gene ontology analysis revealed enrichment mainly in metabolic and cellular processes. Differentially expressed genes analysis showed that low O2 concentrations combined with cold conditions slows the metabolic processes more than just the cold storage, resulting mainly in the suppression of primary metabolism and cold stress response. This is a significant step toward unraveling the molecular mechanism that explains the effectiveness of CA as a tool to prevent CI development on fruits.
Highlights
Prunus persica (L.) Batsch var. nectarina is one of the world’s most important temperate fruit trees due to its fruit’s high nutritional value and pleasing taste (Lauxmann et al, 2012)
A significant decrease in firmness was measured (51 and 8 N, respectively; Table 1); we recorded a significant increase in ethylene synthesis (0.6 and 173.3 μL C2H4 kg−1H−1, respectively) and respiration rate (19 and 87.4 mL CO2 kg−1H−1, respectively; Table 1)
The firmness was similar for all soft conditions (E2, E4, and E4CA), but significant differences in both ethylene synthesis and respiratory rate were observed, which were considerably higher in mealy fruits than the juicy nectarines
Summary
Prunus persica (L.) Batsch var. nectarina is one of the world’s most important temperate fruit trees due to its fruit’s high nutritional value and pleasing taste (Lauxmann et al, 2012). The negative impacts of CS affect fruit quality (Pavez et al, 2013), susceptible varieties such as late-harvest nectarine cultivars stored at low temperatures for more than 2–3 weeks (Zhou et al, 2000). CI development is faster and more intense when susceptible varieties are stored at temperatures between 2.2 and 7.6◦C (Lurie and Crisosto, 2005) These symptoms largely develop after CS during ripening, and the problems are not evident until the consumer eats the fruit because symptoms affect the pulp and not the peel of the fruit (Lurie, 1992; Lurie and Crisosto, 2005; Puig et al, 2015)
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