Wavelength and light intensity enhance growth, phytochemical contents and antioxidant activity in micropropagated plantlets of Urtica dioica L.

Urtica dioica L. (Urticaceae), popularly known as nettle, is a medicinal plant used by the textile, food and pharmaceutical industry. The aim of the current study is to evaluate the influence of different LED wavelengths and light intensity on the growth, phytochemical content and antioxidant activity of Urtica dioica grown in vitro. Nodal segments were taken to MS culture medium under 26, 51, 69, 94 and 130 μmol m−2 s−1, and the following light spectra: blue, red, white, combinations of red and blue (1red/1blue, 2.5red/1blue and 1red/2.5blue) and cool white fluorescent lamps. Leaf area, photosynthetic pigments, total phenolics, total flavonoids and antioxidant activity were evaluated 40 days after culture implementation. Plantlets grown under 94 μmol m−2 s−1 showed better growth and dry weight production outcomes. Phenolic compound and flavonoid production, as well as antioxidant activity were intensified at 130 μmol m−2 s−1. Plantlets grown under 1red/2.5blue produced 5.53 times more phenolic compounds and 8.63 times more flavonoids than plants under fluorescent lights. And dry weight accumulation was favored by wavelength of 2.5red/1blue. The antioxidant activity was influenced by the light intensity, being directly proportional to the increase in light intensity. Increased red light rate induced plantlet etiolation.