In vitro culture of Lippia dulcis (Trev.): light intensity and wavelength effects on growth, antioxidant defense, and volatile compound production

Abstract

Plants of the Verbenaceae family are well known for having constituents with important bioactive properties. The objective of this study was to assess the effect of different light intensities and wavelengths on morphogenesis, accumulation of photosynthetic pigments, antioxidant defense, and production of volatile constituents in Lippia dulcis Trev. plantlets cultured in vitro. Nodal segments were cultured in Murashige and Skoog (MS) basic medium. The plantlets were kept under five light intensities: 20, 57, 78, 102, and 139 μmol m−2 s−1 and under different light spectra: red (R); blue (B); combinations of blue and red %B:%R (30:70; 70:30; and 50:50); white light-emitting diode (LED) (W); green (G); yellow (Y), obtained by LEDs; and cold white fluorescent (FL), for 45 d. Of the light intensities, 139 μmol m−2 s−1 resulted in the greatest accumulation of dry weight (leaf dry weight (LDW), root dry weight (RDW), and total dry weight (TDW)). However, this treatment was responsible for the lowest production of total chlorophyll a and chlorophyll b and carotenoids, in addition to the lowest antioxidant defense by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Of the light wavelengths, the combinations of the B:R spectra (30:70 and 50:50) were responsible for the highest accumulation of dry matter. The content of total phenolic compounds, as well as the antioxidant defense capacity of the total antioxidant capacity (TAC), DPPH, and chelating power assays, was more significant in the B treatment than in the other treatments. It is concluded that the optimal in vitro culture conditions for L. dulcis are reached under a higher light intensity (139 μmol m−2 s−1). For the light spectra, the combinations of 50%B:50%R and 30%B:70%R are the treatments that resulted in the propagation of plantlets with improved conditions for the acclimatization phase.