Responses of phenolic acid and flavonoid synthesis to blue and blue-violet light depends on plant species

Three common culinary herbs were studied in order to find out how manipulation of blue range of wavelength spectrum affects plant growth and chemistry. The studied species were basil (Ocimunt basilicurn), arugula (Eruca saliva) and bloody dock (Rumex sanguineus). It was hypothesized that high-energy short wavelengths induce stress and further increase phytochemical production for light screening. The study was arranged in a greenhouse, where traditional high-pressure sodium lamps served as control treatment. The other two treatments were supplemental blue light (+ B) (max. peak at 450 nm) and supplemental blue-violet (+ BV) light (max. peaks at 420 and 440 nm). LED lights were used to produce these supplementations. Generally light treatments did not induce marked stress as evaluated by chlorophyll fluorescence ratio (Fv/Fm). However, all growth parameters (shoot elongation, leaf biomass, leaf number) tended to be highest in control treatment, except for leaf number in arugula. Phytochemical production of bloody dock was responsive to neither blue light treatments (+ B and + BV). Instead of that, both blue light treatments increased production of phenolic acids in basil, and flavonoids in arugula. In arugula, + BV was even more efficient, indicating the role of flavonoids in protection against UV-A radiation in this species. The role of blue to red light ratio is discussed in relation to quantitative expression in phytochemical synthesis.