LED lighting for reduced nitrate contents in green vegetables

Green leafy vegetables occupy a very important place in the human diet, however, they also represent a group of plants that tend to accumulate nitrates in their tissues. In recent years, nitrate problems have been revived in closed environment intense cultivation systems. In such systems, it is possible to control nitrate metabolism by tailoring controllable environmental parameters. In this study we review the effects of light-emitting diode (LED) lighting spectrum and photosynthetic photon flux density (PPFD) on nitrate assimilation in green vegetables. Experiments were performed in closed environment growth chambers (21/17°C day/night temperature, ~65% relative humidity). Green and red leaf lettuces (Lactuca sativa ‘Lobjoits green cos’ and ‘Red cos’) and tatsoi (Brassica rapa var. rosularis ‘Rosetto’ F(1)) were cultivated under combinations of red (660, 640 nm), blue (445 nm) and far-red (731 nm) LED lighting under a PPFD of 100-300 µmol m(‑2) s(‑1). The activities of nitrate, nitrite, nitrate reductase and nitrite reductase, as well as total protein content were evaluated. Both spectral differences and light intensity have remarkable, species-specific effects on nitrate contents and activities of reducing enzymes.