Improvement of the Growth and Nutritional Quality of Two-leaf-color Pak Choi by Supplemental Alternating Red and Blue Light

Abstract

The aim of the present study was to evaluate the effects of alternating red (660 nm) and blue (460 nm) light on the growth and nutritional quality of two-leaf-color pak choi (Brassica campestris L. ssp. chinensis var. communis). Four light treatments (supplemental alternating red and blue light with intervals of 0, 1, 2, and 4 hours, with a monochromatic light intensity of 100 μmol·m−2·s−1 and a cumulative lighting time of 16 hours per day) were conducted in a greenhouse under identical ambient light conditions (90 to 120 μmol·m−2·s−1 at 12:00 am) for 10 days before green- and red-leaf pak choi were harvested. The results showed that the two-leaf-color pak choi receiving alternating red and blue light exhibited more compact canopies and wider leaves than those under the control treatment, which was attributed to the shade avoidance syndrome of plants. The present study indicated that the biomass of green-leaf pak choi was much higher than that of red-leaf pak choi, but the nutritional quality of green-leaf pak choi was lower than that of red-leaf pak choi, and seemingly indicating that the regulation of metabolism for pak choi was species specific under light exposure. The trends of both biomass and the soluble sugar content were highest under the 1-hour treatment. The contents of chlorophyll a and total chlorophyll in both cultivars (green- and red-leaf pak choi) were significantly increased compared with control, without significant differences among the 1-, 2-, and 4-hour treatments, whereas chlorophyll b exhibited no significant difference in any treatment. Alternating red- and blue-light treatment significantly affected the carotenoid content, but different trends in green- and red-leaf pak choi were observed, with the highest contents being detected under the 1-hour and 4-hour treatments, respectively. With increasing time intervals, the highest soluble protein contents in two-leaf-color pak choi were observed in the 4-hour treatment, whereas nitrate contents were significantly decreased in the 4-hour treatment. Compared with 0 hours, the contents of vitamin C, phenolic compounds, flavonoids, and anthocyanins in two-leaf-color pak choi were significantly increased, but no significant differences were observed in vitamin C, phenolic compounds, and flavonoids among the 1-, 2-, and 4-hour treatments, similar to what was found for the anthocyanin content of green-leaf pak choi. However, the content of anthocyanins in red-leaf pak choi gradually increased with increasing time intervals, with the highest content being found in the 4-hour treatment. Supplemental alternating red and blue light slightly increased the antioxidant capacity [1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging rate and antioxidant power], but no significant differences were observed after 1, 2, and 4 hours of treatment. Taken together, treatment with an interval of 1 hour was the most effective for increasing the biomass of pak choi in this study, but treatment with a 4-hour interval should be considered to enhance the accumulation of health-promoting compounds.

Effect of Interchanging Red and Blue LED Irradiation Sequence on Growth of Lettuce

“…Simultaneous irradiation RB16 induced larger leaf width compared with interchanging irradiation R4/B4 and R8/B8. Our findings were not consistent with results reported by Shimokawa et al (2014), Ohtake et al (2018) and Huang et al (2021), in which, interchanging irradiation Rand B-LED irradiation induced plant growth compared to simultaneous RB16. The discrepancies might be attributed to inadequate light intensity under RB and R/B.…”

“…This occurs because of light dispersing out from the front portion of the growth chamber (refer to Figure 1). In contrast, the combined R-and B-light PPFD used in other similar studies (Huang et al, 2021;Ohtake et al, 2018;Shimokawa et al, 2014) were around more than 100 µmol•m −2 •s -1 . The limitation of PPFD in our experimental setup may be restricted to the RGB LED strips installed in our growth chamber.…”

Amelioration Effect of LED Lighting in the Bioactive Compounds Synthesis during Carrot Sprouting

“…In general terms, red light promotes photosynthesis and improves vegetative growth by increasing the chlorophyll content, and blue light is absorbed by carotenoid pigments, favoring the opening of the stomas [9]. In this sense, also, Huang et al [32] have recently shown that a 4 h interval of supplemental red and blue lights (16 h in total: 1250 kJ m −2 ), alternatively applied, improves the accumulation of phenolic compounds and carotenoids in green-leaf and red-leaf pak choi. However, the ratio of red and blue light must be optimized for each species [38].…”

“…Previous studies found that the combination of blue and red lights, both simultaneously [31] and separately [32], increased the total phenolic content by improving photosynthesis, as well as the malonyl-CoA production, which is associated with the synthesis of phenolic compounds. In this sense, our results demonstrate for the first time that the application of blue and red LED lighting in separate phases of the light cycle during carrot sprouting improved the total phenolic content.…”

Engineered Nanomaterials for Improving the Nutritional Quality of Agricultural Products: A Review

“…Crop growth and development are influenced by climate conditions, which also have an impact on how well-balanced the diet of crops is. Huang et al showed that the growth of leaves of two-leaf Chinese cabbage irradiated alternately with red and blue light was better than that of control treatment, moreover, red and blue light irradiation had an effect on the concentration of chla, total chlorophyll, carotenoids, soluble protein and so on [ 20 ]. In addition, Anza et al showed that the season had an effect on the nutritional quality parameters of tomatoes, and the nutritional quality of tomatoes grown in spring was better [ 21 ].…”