Induction of Antioxidant Metabolites in Moringa oleifera Callus by Abiotic Stresses

Moringa oleifeira has recently been subjected to numerous scientific studies pursuing its biological properties. However, biotechnological approaches promoting the synthesis of pharmacological compounds in this species are still scarce, despite the fact that moringa metabolites have shown significant nutraceutical effects. For this reason, in vitro cultures of moringa callus, obtained from leaf explantation, were subjected to various abiotic stresses such as temperature, salicylic acid, and NaCl, to identify the best growth conditions for the production of high levels of antioxidant molecules. Temperature stresses (exposure to 4 and 45 °C) led to no significant variation in moringa callus, in terms of antiradical metabolites, whereas salicylic acid (200 μM) and NaCl (50-100 μM) affected an increase of total phenolic compounds, after 15 and 30 days of treatment. Overall, the treatment with 100 μM NaCl for 30 days showed the highest free radical scavenging activity, comparable to that measured in moringa leaf. In addition, high doses of NaCl (200 μM) inhibited callus growth and reduced the amount and bioactivity of the secondary metabolites of callus. This study provides useful information to standardize growth conditions for the production of secondary metabolites in moringa in vitro cultures, a biotechnological system that could be employed for a rapid, controlled, and guaranteed production of antioxidant molecules for pharmaceutical purposes.