Effects of different LEDs wavelengths on secondary metabolites accumulation in medicinal plants cultivated in vitro: A review of recent literature

Plant tissue culture is considered a promising tool to industrially enhance secondary metabolites content in plants, especially medicinal ones, whose bioactive compounds are used for pharmaceutical and therapeutic purposes. LED systems are increasingly adopted in tissue cultures compared to other lamp typologies, enabling to alter the metabolic pathways and bioactive compounds content by manipulating light spectral properties. The present work aims at identifying the effect of different LED lighting recipes on secondary metabolites content of medicinal plants cultivated in vitro focusing on recent literature (from 2016 onward). In total, 26 articles were identified, accounting for 137 lighting spectra treatments evaluating phytochemicals accumulation of phenols, anthocyanins, carotenoids, glycosides and alkaloids. Most of the studies adopted a photoperiod of 16 h day-1 (66%) and a PPFD ranging from 30 to 50 μmol m-2 s-1 (69%). Regarding LED lighting quality, different red:blue combinations were the most applied (28%), followed by red, blue and white monochromatic lights (20% each), whereas other wavelengths or combinations were used to a lesser extent. Monochromatic blue light often resulted the most effective in terms of phytochemicals accumulation, although species-specific variability concerning the optimal light spectrum was also evident. From the collected studies, it emerges that tailored LED treatments may efficiently increase secondary metabolites content in tissue cultured medicinal plants.