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.