Influence of the wavelength and intensity of LED lights and cytokinins on the growth rate and the concentration of total cardenolides in Digitalis mariana Boiss. ssp. heywoodii (P. Silva and M. Silva) Hinz cultivated in vitro

Abstract

Digitalis mariana Boiss. ssp. heywoodii is a source of bioactive cardenolides like glucoevatromonoside. The aim was to investigate the in vitro propagation of D. mariana ssp. heywoodii under different cytokinin concentrations and combinations, as well as distinct light intensities and wavelengths, and their effect on plant growth and total cardenolide production. Shoots were inoculated in MS culture medium supplemented with the following 6-benzylaminopurine (BAP) + thidiazuron (TDZ) cytokinin combinations. Shoots were additionally grown under different light intensities (20, 50, 78, 102 and 139 µmol m−2 s−1 LEDs) and wavelength conditions (fluorescent, white, green, blue (B), red (R) LEDs—70%R:30%B, 30%R:70%B, 50%R:50%B). The largest number of shoots was induced at BAP + TDZ concentrations of 0.5 + 0.5; 0.25 + 0.75 and 1.0 + 0.5 mg L−1, with mean values of 8.80, 10.37 and 10.60 shoot explants−1, respectively. The combination of 0.375 + 0.125 mg L−1 of BAP + TDZ (366 mg plant−1) resulted in the highest dry leaf weight. Increased cytokinin concentrations led to a larger number of hyperhydrified shoots and decreased cardenolide production. The absence of cytokinins in the medium resulted in higher contents of total cardenolides (0.310 ± 0.008%, g/g) in leaves. However, the combination of 0.375 mg L−1 BAP + 0.125 mg L−1 TDZ increased the total cardenolide production to 82.52 ± 12.52 mg TC plantlet−1. Light intensity of 139 µmol m−2 s−1 improved plant growth and cardenolide production. With respect to the light spectrum the blue/red wavelength combination encouraged shoot biomass production and elevated total cardenolide contents.