Modulation of VOC fingerprint and alteration of physiological responses after supplemental LED light in green- and red-leafed sweet basil (Ocimum basilicum L.)

Narrowband green (G), blue (B), red (R), and polychromatic (W ‒ R:G:B, 1:1:1) lights were supplemented (250 µmol photon m‒2 s‒1; 5 h d−1; 21 d) to ambient light with Light Emitting Diodes (LED) in green- (‘Tigullio’; TI) and red-leafed (‘Red Rubin’; RR) sweet basil (Ocimum basilicum L.) plants. The aim of this work was to evaluate LED-triggered variations in biometric and morpho-anatomical traits, photosynthesis and secondary metabolite production to ‘photomodulate’ plant performance via monochromatic LED light supplementation. In both the cultivars, light supplementation did not alter plant biomass production compared to controls and at the amplitude applied therein any LED supplementation resulted in oxidative stress, as evidenced by slight changes in chlorophyll fluorescence parameters and H2O2 staining in leaves. Conversely, monochromatic LEDs selectively modulate metabolomics profile in both green- and red-leafed basil; e.g., B lights increased polyphenol content in TI, whilst G light resulted effective in reducing cyanidin-3-coumaroil-glucoside one of the prevalent acylated anthocyanin of RR. Volatilome profile unveiled profound waveband-dependent alterations though consistently eugenol, characterised by a clove flavor, and also considered one of the major toxic compounds in sweet basil, decreased with all the LED treatments, making green-leafed basil a more pleasant and safer product. Our dataset offers the clear evidence that monochromatic LED light supplementation represents a valid tool to modulate the accumulation of targeted secondary metabolites in planta.