Color is one of the most important indicators of fruit quality for consumers and it also decides the market value. Different cultivars of paprika produce different colored fruit, with eight colors being recognized: red, yellow, orange, green, white, brown, purple, and black (Simonne et al., 1997). Among these, purple fruit have particularly good market potential because purple vegetables are rare. However, although purple cultivars change color from green to purple during development, they then become red at maturity (Fig. 1), making the commercial use of purple paprika problematic.
The purple anthocyanin nasunin (delphinidin-3-p-coumaroyl-rutinoside-5-glucoside) was isolated from eggplant (Solanum melongena L.) peels by Kuroda and Wada (1933). It is also one of the major pigments responsible for the purple coloration of the paprika fruit (Aza-González and Ochoa-Alejo, 2012; Lightbourn et al., 2008). Thus, the change in purple color intensity that occurs in paprika fruit during development appears to be caused by changes in the anthocyanin contents, suggesting that both anthocyanin biosynthesis and degradation are involved in this process.
Anthocyanin biosynthetic activity can be estimated by measuring the expression levels of anthocyanin biosynthesis–related genes, which are regulated by a complex of transcription factors that are encoded by the MYB, basic helix–loop–helix (bHLH), and WD40-repeat (WDR) genes (Koes et al., 2005; Ramsay and Glover, 2005; Xu et al., 2015). In paprika, the expressions of some anthocyanin biosynthesis–related genes are upregulated by MYB and MYC/bHLH (Aguilar-Barragán and Ochoa-Alejo, 2014; Lu et al., 2018; Zhang et al., 2015), and unripe fruit have higher expressions than ripe ones of MYB in the purple inbred line 5226 (Borovsky et al., 2004) and of anthocyanin biosynthesis–related genes in the purple cultivars Arvol and Uvilla (Aza-González et al., 2013). The enzymatic degradation of anthocyanin has also been detected in plants (Barbagallo et al., 2007; Fang et al., 2015; Vaknin et al., 2005; Zipor et al., 2015), which may involve peroxidases, polyphenol oxidases, and β-glucosidases (reviewed by Oren-Shamir, 2009).
Based on this information, we investigated the mechanism behind the change in purple coloration in the paprika fruit by examining changes in the anthocyanin biosynthesis and degradation activities in the fruit of the cultivar Mavras, which are dark purple when immature, and Tequila, which are lilac when immature. We also studied the synchrony between content changes in anthocyanins and both chlorophylls (green pigments) and carotenoids (red pigments) during fruit development to determine whether they are regulated by the same mechanism.
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Primers used for quantitative polymerase chain reaction (qPCR).
Retention time and spectral data for chlorophylls and carotenoids that were separated by high-performance liquid chromatography from the reference compounds and extracts from the fruit of the paprika cultivars Mavras and Tequila at 20 d after pollination (DAP) (chlorophylls) or 60 DAP (carotenoids).