Quality and intensity of light affect Lippia gracilis Schauer plant growth and volatile compounds in vitro

Abstract

The aim of this study was to evaluate the effects of different intensities and quality of light and explant type on the growth of and volatile compounds in Lippia gracilis in vitro. The treatments were as follows: light intensities of 26, 51, 69, 94, or 130 µmol m−2 s−1 from fluorescent lamps and light-emitting diode (LED) lamps at different wavelengths, namely, white, red, blue, and combinations of red and blue light at ratios of 2.5:1 and 1:2.5, respectively, and two explant types, namely, nodal and apical segments. On the 30th day of culture on half-strength Murashige and Skoog (Physiol Plant 15(3):473–497, 1962) medium, growth, production of photosynthetic pigments, chlorophyll a and b, total chlorophyll, carotenoids, and volatile constituents (using headspace gas chromatography-mass spectrometry) were analyzed. The light quality and intensity significantly influenced the in vitro growth of L. gracilis. The apical segments were superior in all parameters evaluated compared to nodal segments. The number of segments plantlet−1, root length, and leaf, shoot, root, and total weight were higher with increasing light intensity, especially under the 94 µmol m−2 s−1 treatment, for both explant types. The red light showed the highest leaf (32.28 mg plantlet−1) and total (58.33 mg plantlet−1) dry weight of all the light qualities. Major constituents, namely, ρ-cymene, γ-terpinene, thymol, carvacrol, and E-caryophyllene, were identified, regardless of light conditions. The amount and composition of volatile compounds varied according to light intensity and quality. Low intensity (26 µmol m−2 s−1) increased γ-terpinene content (12.42%) and concomitantly decreased carvacrol (38.52%). Blue LED light showed higher production of carvacrol (48.11%).