Crescimento in vitro e acúmulo de compostos antioxidantes de Urtica dioica L. micropropagadas sob diferentes condições de ventilação natural e luminosidade

Abstract

Urtica dioica L. (Urticaceae), popularly known as "stinging nettle", is a medicinal plant exploited by the textile, food, and pharmaceutical industries. Recently, the species has received attention from researchers for presenting evidence of anticancer activity due to its antioxidant compounds. The intensity, light quality and type of cultivation system are factors that directly influence the growth and secondary metabolism of medicinal plants. Therefore, this study aimed to evaluate different intensities, light qualities, and the use of natural ventilation system in the growth and accumulation of secondary compounds in micropropagated U. dioica plantlets. In the light intensity experiment, nodal segments were cultured in MS medium under the irradiances 26, 51, 69, 94, and 130 μmol m -2 s -1 , obtained with LED lamps. In the light quality experiment, nodal segments were grown in MS culture medium under LED lamps: red; blue; 1 red:1blue; 2.5 red:1 blue; 1 red: 2.5 blue; white, and under cold white fluorescent lamp. In the experiment with the natural ventilation system (SVN), nodal and apical segments with a pair of leaves were grown in MS culture medium in the presence and absence of 30 g L -1 of sucrose. Four types of culture systems were tested: conventional system (SC), natural ventilation system with one membrane (SVN1), two membranes (SVN2) and four membranes (SVN4). After 40 days, the growth, leaf area, dry matter, photosynthetic pigments, total phenolic compounds, total flavonoids and antioxidant activity were evaluated in all three experiments. Plantlets grown under 94 μmol m -2 s -1 showed superior growth and dry matter yields in vitro. The production of phenolic compounds, flavonoids and antioxidant activity was intensified at 130 μmol m -2 s -1 . The use of 1 red: 2.5 blue LED provided increased the concentration of phenolic compounds by 5.53 times and 8.63 times in flavonoid concentration, compared to the use of fluorescent lamps. The LED 2.5 red:1blue favored the growth and accumulation of dry matter in vitro. The natural ventilation system was superior to the conventional one regarding the indices of growth. Apical segments grown in culture medium supplemented with sucrose and the use of SVN1 and SVN2 promoted the best in vitro growth results. The antioxidant activity is directly influenced by the increase in light intensity. Increasing the proportion of red light induces etiolation. The addition of sucrose in the culture medium promotes rooting and flavonoid accumulation. The absence of sucrose induces leaf dry matter production.