Functional difference between betacyanins in vitro and in planta: Betanin and amaranthin enhance tyrosine-related metabolites in mustard seedlings

Betalainic plants accumulate biosynthetically related betacyanins such as betanidin, betanin (betanidn-5- O -glucoside), and amaranthin [betanidin-5- O -(2′- O -glucuronyl)-glucoside]. In such plants, these pigments are involved in stress tolerance and other physiological roles. These pigments are pharmacoactive and also used as food colorants, smart indicators in packaging films, and others. Herein, we investigated the effects of incremental substitution in their structures using density functional theory (DFT), in vitro antioxidant activity, cytotoxicity, and seedlings of Brassica campestris L., which is a betalain-devoid crop plant. The results showed betanin’s better electron-donating potential, amaranthin’s better in vitro antioxidant activity, and synergistic in vitro cytotoxic effect of all the three above-mentioned betacyanins. Individual betacyanins or in combinations of two of them were not cytotoxic. Betanin (50 mmol/L) produced comparable growth-promoting effect with 24-epibrassinolide (EBR; 10 μmol/L), a brassinosteroid. EBR and betanin did not affect total chlorophylls, but amaranthin enhanced them. Betanin enhanced tyrosine and ascorbic acid in B. campestris seedlings. Amaranthin neither produced a significant growth-promoting effect nor a comparable tyrosine-enhancing effect with betanin. Taken together, our findings establish that betanin is a physiologically more effective compound in planta , particularly in betalain-devoid B. campestris . Considering the importance of tyrosine and ascorbic acid in our diet and betanin’s ability to enhance them in B. campestris , pre-harvest treatment with betanin or betanin-containing formulations may be recommended to enhance the nutritional quality.