3.8 Elevated anthocyanin content under red and blue supplemental light
Metabolite profiling with UPLC-HDMS was performed from light treated berry samples after 6 days (same time point for transcriptome libraries). The red, blue and control samples from the metabolite analysis were separated in the first component in the Principal Component Analysis (PCA), explaining 32.3% of the variation (Figure S8). The heat map analysis of metabolite profiling data shows large number of significantly different metabolites (407 metabolites of total 700, ANOVA, p<0.05); anthocyanins localized in the middle part of the clusters (Figure S9). The results showed consistent and significant increase in all the anthocyanin compounds under both the red and blue light treatments when compared with control (Figure 8a). Delphinidin galactosides/glucosides were detected 11-fold higher in red light when compared to other light treatments followed by significant increase in all the cyanidin, petunidin and malvidin glycosides (Figure 8a). Also, the total anthocyanins quantified in ripening berries (S4) after 12 days of light treatment showed higher amounts of anthocyanin accumulation in red light followed by blue light treatments compared with ambient white light control (Figure 8b).
Similar trend was also observed in S5 stage fully ripe berries although the difference was not as apparent (Table S10). Quantitative analysis with HPLC confirmed that the two major delphinidin glycosides, delphinidin-3-galactoside and delphinidin 3-arabinoside, were found at significantly higher amounts in red light treatment, contributing to the increase in total anthocyanin content (4760 mg 100g-1DW) compared to that of blue light and the control samples. The trend is followed by the increase in levels of cyanidin and petunidin glycosides in red light treated berries. A very low amount of peonidin-3-glucoside was detected in all the samples which was not generally influenced by different light treatments (Table S10).
Pearson’s correlation matrices between the dominantly found anthocyanins quantified using HPLC (delphinidin 3-galactoside and delphinidin 3-arabinoside) and the transcript levels related to the flavonoid, carotenoid, ABA pathway genes, and ABA-receptors from both light treatments (Figure 9) indicated strong links between ABA and anthocyanin biosynthesis especially with red light. We also found statistically significant positive correlations among gene-metabolite interactions for red light compared to blue light treatment.