The role of plant-derived melanin in enhancing <i>in vitro</i> growth and nutrient accumulation in potato varieties

Background: Melanins are versatile biopolymers found in a wide range of living organisms, contributing to the diverse colors observed in nature. Beyond their pigmentation role, melanins exhibit a variety of biological activities, including antioxidant, antitoxic, antitumor, photoprotective, antimicrobial, and radioprotective properties. These attributes make melanins valuable in fields such as medicine, pharmaceuticals, and agriculture. In this study, we investigated grape marc, a byproduct of wine production, as a novel source of water-soluble melanin extracted using sodium hydroxide. This approach not only repurposes agricultural waste but also explored melanin's role in optimizing in vitro plant cultivation. We evaluated the impact of melanin on the biochemical properties of potato plants, focusing on improvements in growth, rhizogenesis, and the nutritional composition of tubers. Objective: The aim of this study was to evaluate the effects of plant-derived melanin on the in vitro growth characteristics and biochemical composition of two potato varieties. Methods: This study took place in the tissue culture laboratory at the Scientific Center of Agrobiotechnology from 2021 to 2024. Apical meristems from the Nevsky and Impala potato varieties were used for in vitro regeneration. The research focused on the in vitro growth and adaptation of these plants under different melanin concentrations. Key growth parameters, chlorophyll content, and biochemical composition were analyzed to assess the impact of melanin on potato development. Results: The study found that melanin at a concentration of 0.028% significantly enhanced the in vitro growth and rhizogenesis of potato microstems, with optimal results in root number (12.30 per shoot) and shoot length (16.91 cm). Plants also showed earlier and more vigorous root formation, resembling an auxin-like effect. Higher melanin concentrations reduced these benefits. Additionally, plants treated with 0.028% melanin had a high acclimatization success rate (96%) and improved biochemical composition in tubers, with increases in dry matter, sugars, starch, and ascorbic acid, particularly in the Nevsky variety. Conclusion: Melanin significantly stimulated the in vitro growth and development of potato plants. Increasing melanin levels to an optimal threshold accelerated rhizogenesis and promoted vigorous root and shoot growth, evidenced by increased length and thickness. Acting similarly to auxin, melanin not only encouraged root formation but also enhanced shoot development, leading to improved plant adaptation. Additionally, melanin influenced the biochemical composition of potato tubers, including their nutritional content. These findings highlight the crucial role of melanin concentration in optimizing the growth and biochemical properties of potato varieties. Keywords: in vitro propagation, potato, melanin, plant adaptation, biochemical compound, micropropagation