Growth and Bioactive Compound Synthesis in Cultivated Lettuce Subject to Light-quality Changes

Abstract

<jats:p>This study aimed to determine the effect of changes in light quality on the improvement of growth and bioactive compound synthesis in red-leaf lettuce (<jats:italic>Lactuca sativa</jats:italic> L. ‘Sunmang’) grown in a plant factory with electrical lighting. Lettuce seedlings were subjected to 12 light treatments combining five lighting sources: red (R; 655 nm), blue (B; 456 nm), and different ratios of red and blue light combined with three light-emitting diodes [LEDs (R9B1, R8B2, and R6B4)]. Treatments were divided into control (continuous irradiation of each light source for 4 weeks), monochromatic (changing from R to B at 1, 2, or 3 weeks after the onset of the experiments), and combined (changing from R9B1 to R8B2 or R6B4 at 2 or 3 weeks after the onset of the experiments). Growth and photosynthetic rates of lettuce increased with increasing ratios of red light, whereas chlorophyll and antioxidant phenolic content decreased with increasing ratios of red light. Individual phenolic compounds, including chlorogenic, caffeic, chicoric, and ferulic acids, and kaempferol, showed a similar trend to that of total phenolics. Moreover, transcript levels of phenylalanine ammonia-lyase (<jats:italic>PAL</jats:italic>) and chalcone synthase (<jats:italic>CHS</jats:italic>) genes were rapidly upregulated by changing light quality from red to blue. Although the concentration of bioactive compounds in lettuce leaves enhanced with blue light, their contents per lettuce plant were more directly affected by red light, suggesting that biomass as well as bioactive compounds’ accumulation should be considered to enhance phytochemical production. In addition, results suggested that growth and antioxidant phenolic compound synthesis were more sensitive to monochromatic light than to combined light variations. In conclusion, the adjustment of light quality at a specific growth stage should be considered as a strategic tool for improving crop yield, nutritional quality, or both in a plant factory with electrical lighting.</jats:p>

How Do White LEDs’ Spectra Affect the Fresh Weight of Lettuce Grown under Artificial Lighting in a Plant Factory?—A Statistical Approach

“…As reported in a pioneering study [19], an increase in blue light facilitates plant growth at very low levels of %PFD (<16%), but its further increases give negative effects on it [7] [20]. In the most detailed study on the effects of blue and red lights on plant growth using narrow-spectrum, high-peak LEDs [21], it was shown that the dry weight of lettuce declined monotonically as blue light increased, over 11 treatments for %PFD, from 13% to 100%. Since the response curve of red light is the reverse of that of blue light emitted by a narrow-spectrum RB-LED, the lettuce yield increased monotonically as red light increased from 0% to 87% PFD and remained at the same level for the range of 87% -100% PFD [21].…”

“…In the most detailed study on the effects of blue and red lights on plant growth using narrow-spectrum, high-peak LEDs [21], it was shown that the dry weight of lettuce declined monotonically as blue light increased, over 11 treatments for %PFD, from 13% to 100%. Since the response curve of red light is the reverse of that of blue light emitted by a narrow-spectrum RB-LED, the lettuce yield increased monotonically as red light increased from 0% to 87% PFD and remained at the same level for the range of 87% -100% PFD [21]. For a given light intensity at the surface of cultivation panels, plant growth is facilitated as the "warmness" of LEDs increases, until the turning point is reached for any light source including red and blue.…”

Both Multi-Segment Light Intensity and Extended Photoperiod Lighting Strategies, with the Same Daily Light Integral, Promoted Lactuca sativa L. Growth and Photosynthesis

“…In addition, the rhythm of these processes can change periodically during a single day. Previous lighting strategies have ignored the effects of photoperiod on circadian rhythm, missing the opportunity to use the circadian rhythm to benefit the growth of crops in PFALs [21][22][23][24].…”

Quantitative Evaluation of Electric Light Recipes for Red Leaf Lettuce Cultivation in Plant Factories

“…Phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) are key enzymes in the biosynthetic pathway of anthocyanin, and high blue light quality treatments (at least 50% of total PPFD) can increase PAL activity (Heo et al, 2012). Moreover, when red leaf lettuce was cultivated for 1 week, first with red light and then with blue light, substantial accumulations of PAL and CHS were found (Son et al, 2017). This indicated that blue light can stimulate the biosynthesis of these two enzymes to increase the AC; however, the FW of lettuce tended to be decreased.…”