How monochromatic and composed light affect the kale ‘Scarlet’ in its initial growth stage

Interest in vegetables at their microgreen stage, especially those from the Brassicaceae family, has constantly grown due to their numerous health-promoting compounds. Brassica oleracea convar. acephala var. sabellica cv. Scarlet with purple leaf discolouration was used in the study. Four LED lighting treatments were applied: white light (control), monochromatic blue (430 nm), monochromatic red (660 nm) and purple, i.e., blue (30% in spectrum, 430 nm) mixed with red (70%, 620 nm and 660 nm in equal shares). Photosynthetic photon flux density (PPFD) was 100 µmol m–2 s–1, photoperiod – 16 h light. The purple light promoted the cotyledon growth but decreased the soluble sugars content. The blue light significantly enhanced the anthocyanins synthesis and the radical scavenging activity (RSA). While under white light, the highest concentration of free amino acids and the lowest RSA were observed. As regards the phenolic compounds and photosynthetic pigments content, the reaction of kale to white light was similar to those observed under the purple and red light conditions. The experiment discussed here is of great practical importance and reveals the need for more in-depth research.