## 4 Discussion  
The challenges faced by mankind during the last decade are the drivers for the search for and development of innovative technologies for sustainable production of foods and plant-derived goods. Cultivation of plant cells is a promising branch of cellular agriculture with amazing potential in the large scale production of foods and technical goods [39; 41; 45]. The black chokeberry (_Aronia melanocarpa_) is a rich source of pigments (anthocyanins), polysaccharides and valuable antioxidants (flavonoids, phenolic acids and flavan-3-ol) [3; 6; 11; 12; 13; 58; 59]. Because many of these secondary metabolites have proven health benefits, the Aronia was classified as a \"superfood\" [7; 11]. Early reports demonstrated the potential of _Aronia melanocarpa_ shoot and callus cultures for in vitro production of valuable compounds [27; 28]. The effects of varying the concentration of used growth regulators [28] and different cultivation conditions, including light [33], on phenolics production were investigated as well, and the potential of _Aronia_ in vitro cultures for production of therapeutic, health-promoting and cosmetic ingredients was suggested. In this work, we demonstrated that the _Aronia melanocarpa_ cell suspension culture accumulates a significant amount of biomass and has great potential for the development of biotechnology for sustainable production of food supplements. When cultivated in darkness, Aronia cells accumulated 8.68 \(\pm\) 0.06 g/L dry biomass, reaching a growth index of 2.43 \(\pm\) 0.06 for seven days. This is very high productivity, compared to _A. melanocarpa_ shoot cultures, which reach a growth index of 3.78 \(\pm\) 0.07 after four weeks' cultivation in darkness [34].Data showed that light can induce changes in cell morphology, initiate the biosynthesis of anthocyanins and significantly increase the content of phenolic compounds (Figures 1 and 2, Table 1). When cultivated under illumination (photoperiod 16 h light and 8 h dark), Aronia cell suspension accumulates 1812.79 \(\pm\) 46.19 \(\upmu\)g/g DW (or 181.28 mg/100 g DW) chlorogenic acid, which is much higher than the reported amount in _A. melanocarpa_ shoots (127.77 \(\pm\) 9.41 mg/100 g DW) cultivated under illumination with blue light (photoperiod 16 h light and 8 h dark) for four weeks [31]. The effect of light cycles on phenolic compounds was dramatic, as was demonstrated by heatmap clustering and PCA. It has been reported previously that light can increase the level of secondary metabolites in plant cell suspensions [60]. The positive effect of light on anthocyanins production has been well studied in grape cell suspension cultures [48]. However, this effect has not been studied in _A. melanocarpa_ in vitro cultures. Here, we demonstrated \begin{table}
\begin{tabular}{l l l} \hline \hline
**Antioxidant Activity * & **Light Cycles** & **Dark** \\ \hline DPPH & 21.36 \(\pm\) 0.11 a  & 4.27 \(\pm\) 0.17 b  \\ TEAC & 10.08 \(\pm\) 0.07 a  & 1.41 \(\pm\) 0.12 b  \\ FRAP & 34.85 \(\pm\) 0.46 a  & 4.26 \(\pm\) 0.08 b  \\ CUPRAC & 126.74 \(\pm\) 1.49 a  & 18.44 \(\pm\) 0.54 b  \\ Total Phenolic ** & 8.17 \(\pm\) 0.04 a  & 1.58 \(\pm\) 0.03 b  \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Antioxidant activities of extracts from _Aronia melanocarpa_ cell suspension cultures cultivated under light cycles and in darkness. \begin{table}
\begin{tabular}{l l l} \hline \hline  & \multicolumn{2}{c}{**Total Phenolic**} \\ \cline{2-3}  & **r * & **_p_-Value** \\ \hline CUPRAC & 0.99987 & 0.000000023681 \\ TEAC & 0.99991 & 0.00000013358 \\ DPPH & 0.99982 & 0.000000045980 \\ FRAP & 0.99985 & 0.000000035341 \\ \hline \hline \end{tabular}  
*Pearson correlation coefficients.  
\end{table} 
Table 3: Correlations between antioxidant activity and total phenolic content of extracts from _Aronia melanocarpa_ cell suspension culture. that light cycles can initiate pigment production in _A. melanogaster_ cells and the content of total anthocyanins-rich 0.011 \(\pm\) 0.001 mg cyanidin-3-glucose equivalents/g DW.