Short Cold Storage Enhances the Anthocyanin Contents and Level of Transcripts Related to Their Biosynthesis in Blood Oranges

Abstract

The health benefits associated with the consumption of anthocyanin-containing foods are extensively documented. Mature fruits of blood oranges and their hybrids are characterized by the presence of these bioactive pigments, the abundance of which can be enhanced by storing fruit at cooling nonfreezing temperature. In this work the effects of short low-temperature exposure (4 °C × 15 days) upon orange anthocyanin content and the expression of structural genes belonging to the pigment biosynthesis pathway were investigated. The results highlight that anthocyanin levels of fruit exposed to cold sharply increase, reaching, after 6 days of storage, a value 8 times higher than that observed in the time zero samples, thus suggesting that fruit with enhanced health-related attributes might be obtained at this storage stage. The analysis of gene expression shows that the amount of transcripts of all considered genes (CM1, PAL, CHS, DFR, ANS, UFGT, and GST) sharply increased after 3-6 days of cold storage, confirming previous data showing that the biosynthesis of anthocyanins is a cold-regulated pathway. By comparing the expression of selected genes (PAL, DFR, and UFGT) between blood and common oranges, it turns out that those genes strictly involved in anthocyanin biosynthesis are not cold responsive in common oranges. Moreover, the data highlight that the EST encoding the transcription factor NAC domain protein is selectively induced by cold in blood oranges but not in common oranges, thus proposing it as a candidate gene specifically involved in blood orange response to cold exposure.

Molecular genetics of blood‐fleshed peach reveals activation of anthocyanin biosynthesis by NAC transcription factors

“…In raspberry, a candidate gene encoding a NAM/CUC2-like protein has also been identified in a QTL locus on LG1, which is responsible for the accumulation of cyanidin and pelargonidin pigments (Kassim et al, 2009). In orange, a NAC TF is proposed to be involved in anthocyanin accumulation during the response of blood orange to cold exposure (Crif o et al, 2012). Interestingly, raspberry, like peach, is also a member of the Rosaceae family.…”

“…SQUAMOSA and SEPALLATA MADS box TFs have also been reported to be associated with the accumulation of anthocyanin in bilberry (Jaakola et al, 2010) and pear (Wu et al, 2013), respectively. More recently, MdCOP1 has been demonstrated to be involved in the ubiquitination and degradation of the MdMYB1 protein under dark conditions in apple and a NAC TF has been proposed to be involved in the regulation of anthocyanin accumulation during the response of blood orange to cold exposure (Crif o et al, 2012). In addition, epigenetic mechanisms such as promoter methylation of R2R3 MYB genes have also been shown to play an important role in the regulation of anthocyanin accumulation in apple (Telias et al, 2010) and pear (Wang et al, 2013) fruits.…”

<i>Citrus</i> Flavonoids and Human Cancers

“…The basic chemical structure of anthocyanin is shown in Figure 2-D. Anthocyanins occur in all tissues of higher plants, including leaves, stems, roots, flowers, and fruits. In Citrus, anthocyanins were studied in blood oranges [20]. They were found in the epicarp, but they also colour the mesocarp of oranges.…”

Pigments in Citrus

“…On the contrary, DFR, ANS, and UFGT are at much lower or no detected expression in blond cultivars [103,113]. Anthocyanin content increases during fruit ripening but varies greatly among blood orange cultivars [88,113] and upon other genetic factors and environmental conditions such as temperature [87,89,114].…”