Light spectral effects on phenolic compounds inPerilla frutescensleaves as related to the leaf age, color and duration of exposure

Abstract

We aimed to evaluate the effects of light spectral components on the phenolic compounds in young and mature green and red perilla leaves seeking to raise plants with increased antioxidant and nutritional value. Plants were cultivated in phytotron (21/17°C) under experimental light emitting diode (LED) based lighting (18 h, 300 µmol m-2 s-1) the whole 30 days growth cycle (long-term exposure) or transferred from high pressure sodium lighting to experimental LED lighting for the last 3 days of experiment (short-term exposure). Experimental lighting spectra consisted of sole red 638 or 665 nm LED light (300 µmol m-2 s-1) or the combination of red 665 nm with 50 µmol m-2 s-1 of blue 455, yellow 595, green 520 nm or 15 µmol m-2 s-1 of UV-A 385 nm light (total PPFD of 300 µmol m-2 s-1 maintained). Sole red light promoted accumulation of phenolic compounds in young red and green perilla leaves both after short-term and long-term exposure, when supplemental blue light had significant effect only in mature leaves. In young green perilla leaves higher contents of phenolic compounds were determined after short-term UV-A exposure. The higher contents of phenolic compounds under different light spectra exposure correlates with higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity after long-term exposure in green perilla and both after long and short-term exposure in red perilla leaves.