## 3 Discussion  
Plant-food is the main dietary source of AsA and polyphenols for humans. For this reason, increasing importance and value is currently given to horticultural products with high content of antioxidants [32]. The identification of varieties with higher level of health-promoting compounds provides viable opportunities not only to offer high-quality products, but also to improve our understanding of the complex dynamics that underlies the accumulation of these beneficial compounds [33]. A preliminary study on 18 local varieties identified two varieties with low and high accumulation of antioxidants (unpublished). The phytochemical changes that occurred during maturation indicated that a significant difference was not only relative to tAsA and dAsA content, but also in their accumulation dynamic in fruit. Overall, AsA content positively correlated with the fruit stage, as in other pepper varieties as well as other horticultural species [34; 35; 36; 37]. However, only for the higher accumulating variety PEP1, the major increment in AsA (47%, based on fresh weight) was produced during the transition from mature green to red ripe stage, a phase in which chloroplasts turn into chromoplasts. The lower accumulating PEP10 variety did not show a significant increase of AsA from mature green to red, which was not only of dietary relevance, but may affect the consumption and destination of use. Finally, in view of the limited difference in total polyphenols at fruit maturity, the data imply a higher nutritional value of PEP1, considering that the amount of vitamin C and polyphenols highly correlates with the antioxidant capacity in plants [1]. Differences in the level of AsA among pepper genotypes have been already reported by analysing fruits [34; 38]. To understand if the observed variation is organ-specific, we quantified the tAsA, dAsA, and polyphenols in leaves. The higher accumulation in fruits and in leaves of PEP1 suggests that both constitutive (or at least organ-independent) and inducible mechanisms are responsible for different  
Figure 6: Heatmap of the correlations between gene expression states and tAsA or dAsA in pepper fruits. Gradation from red to green represents negative from positive correlations according to the color scale at the bottom. Asterisks indicate a statistical significant correlation (*: \(p<0.05\); **: \(p<0.01\)). accumulation of the bioactive compounds. Moreover, the observed variability between the varieties also underlines the value of local pepper germplasm, which may also be relevant for other metabolic traits [38]. In the future, an analysis of a wider panel of varieties will have to confirm the predictive value of a comparative analysis of the AsA content in leaves, a strategy that can provide obvious advantages for screening large populations. To shed light on the mechanisms involved in the regulation of AsA accumulation, we quantified the expression level of genes belonging to the pathways for AsA de novo synthesis, degradation and recycling. A more comprehensive understanding of all the genes involved in AsA metabolism could be addressed exploiting the power of NGS technologies. While the dynamic of the gene expression during maturation has been previously investigated [34; 39], our aim was to compare behavior of the genes in the two contrasting varieties. Their relative gene expression analysis indicated that the increasing differences in AsA concentration during ripening are associated with a higher induction of genes involved in AsA biosynthesis. In comparison with leaves, additional pathways (e.g., myo-inositol and D-galacturonic acid) should contribute to the observed difference in sink tissues, as it was also observed for two tomato varieties with different levels of AsA in fruit [40]. In several studies, quantification of transcripts has been performed taking the earliest analysed stage as a reference. Under this perspective, the gene expression has a tendency to reduce towards maturation, while total ascorbate concentration increases.