Light quality modulates light signal perception and transduction
In natural conditions, plants encounter varying light spectral conditions. For example, in the latitudes close to Arctic circle, the radiation flux from a distinct solar spectrum (UV-A/B ratio, blue and red/far-red wavelengths) changes compared to southern latitudes and this has been shown to favor higher accumulation of flavonoids in northern vegetation, including wild bilberries (Jaakola & Hohtola 2010; Zoratti et al., 2014a). Delphinidins are the major class of constituting anthocyanins found abundant in northern clones compared with higher cyanidin proportions found in southern clones (Zoratti et al., 2016). Also, in forests the top canopy absorbs most of the essential red and blue wavelengths and only the green and far-red wavelengths are reflected by foliage to lower parts of the plant (Holopainen et al., 2018). In bilberry, populations grown under direct sunlight have demonstrated increased bioactive compounds and bioavailability compared with plants growing under forest canopy (Eckerter et al., 2019). However, the even distribution through the foliage can be achieved by modern energy efficient LEDs because the irradiation maxima from these supplemental lightings are often higher than plant’s absorption peaks. Our study showed that during the red light LED treatment, PhyBexpression was upregulated together with COP1 and HY5 , the key genes involved in photomorphogenesis, alongside photoperiodism-related early flowering (ELF3 ) and CK2αgenes (Figure 5). On the other hand, the blue light up-regulated cryptochrome (CRY2 ) but down-regulated COP1 and HY5in tandem as its photoreactive mechanism which might reveal an early photomorphogenesis occurred upon light treatment as a spontaneous response. It is also to be noted that bHLH6 (MYC2), which is a negative regulator of blue light induced photomorphogenesis and was positively expressed (Yadav et al., 2005), might have played a crucial role in blue light signaling mechanism.