• Journal of Bio-Environment Control
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• v.27 no.3
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• pp.222-230
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• 2018

This study aimed to determine effects of light-emitting diodes on plant growth, leaf morphology and cell elongation of two cultivars ('World-star' and 'Sushiro') of Spinacia oleracea. Plants were grown in a NFT system for 25 days after transplanting (DAT) under the LEDs [White (W), Red and Blue (RB, ratio 2:1), Blue (B), Red (R) LED] under the same light intensity and photoperiod ($130{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, 12 hours). The 'World-star' variety was significantly higher in shoot fresh and dry weights, leaf number, and leaf area than the 'Sushiro' variety. For the 'World-star' variety, the two treatments of mixed light (RB) and red light (R) showed a 35% higher shoot dry weight than that of blue light (B) and white light (W) at 25 DAT. In the 'Sushiro' variety, mixed light (RB) treatment, which had the highest shoot fresh and dry weights, showed 40% higher than the white light (W) treatment, which had the lowest shoot fresh and dry weights. Both varieties showed leaf epinasty symptom at 21 DAT only in both mixed light (RB) and red light (R), and red light (R) treatment showed significantly higher symptom than mixed light (RB), indicating the leaf epinasty is associated with red light. Microscopic observations of the cell size in the leaf center and edge parts showed that the cell density of leaf edge under the red light (R) was lower than that in leaf center, supporting previous reports that suggest an association of the cell size difference between the leaf center and edge with the leaf epinasty occurrence. Since the blue light (B) plays a role in alleviating the epinasty symptom caused by the red light (R), it seems necessary to identify the appropriate mixing ratio of the two light sources. In addition, the World-star variety seems to be more suitable for the cultivation of plant factory using LED light sources.

• Journal of Bio-Environment Control
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• v.28 no.1
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• pp.1-8
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• 2019

The study aimed to determine effects of light emitting diode (LED) and the ultraviolet radiation (UVA) light of plant factory on plant growth and ascorbic acid content of spinach (Spinacia oleracea cv. Shusiro). Plants were grown in a NFT (Nutrient Film Technique) system for 28 days after transplanting with fluorescent light (FL, control), LEDs and UVA (Blue+UVA (BUV), Red and Blue (R:B(2:1)) + UVA (RBUV), Red+UVA (RUV), White LED (W), Red and Blue (R:B(2:1)), Blue (B), Red (R)) under the same light intensity ($130{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$) and photoperiod (16/8h = day/night). All the light sources containing the R (R, RB, RUV, and RBUV) showed leaf epinasty symptom at 21 days after transplanting (DAT). Under the RUV treatment, the lengths of leaf and leaf petiole were significantly reduced and the leaf width was increased, lowering the leaf shape index, compared to the R treatment. Under the BUV, however, the lengths of leaf and leaf petiole were increased significantly, and the leaf number was increased compared to B. Under the RBUV treatment, the leaf length was significantly shorter than other treatments, while no significant difference between the RBUV and RB for the fresh and dry weights and leaf area. Dry weights at 28 days after transplanting were significantly higher in the R, RUV and BUV treatments than those in the W and FL. The leaf area was significantly higher under the BUV treatment. The ascorbic acid content of the 28 day-old spinach under the B was significantly higher, followed by the BUV, and significantly lower in FL and R. All the integrated data suggest that the BUV light seems to be the most suitable for growth and quality of hydroponically grown spinach in a plant factory.

• Journal of Bio-Environment Control
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• v.32 no.4
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• pp.342-352
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• 2023

Ultra-violet (UV) light is one of abiotic stress factors and causes oxidative stress in plants, but a suitable level of UV radiation can be used to enhance the phytochemical content of plants. The accumulation of antioxidant phenolic compounds in UV-exposed plants may vary depending on the conditions of plant (species, cultivar, age, etc.) and UV (wavelength, energy, irradiation period, etc.). To date, however, little research has been conducted on how leaf thickness affects the pattern of phytochemical accumulation. In this study, we conducted an experiment to find out how the antioxidant phenolic content of kale (Brassica oleracea var. acephala) leaves with different thicknesses react to UV-A light. Kale seedlings were grown in a controlled growth chamber for four weeks under the following conditions: 20℃ temperature, 60% relative humidity, 12-hour photoperiod, light source (fluorescent lamp), and photosynthetic photon flux density of 121±10 µmol m^-2 s^-1. The kale plants were then transferred to two chambers with different CO₂ concentrations (382±3.2 and 1,027±11.7 µmol mol^-1), and grown for 10 days. After then, each group of kale plants were subjected to UV-A LED (275+285 nm at peak wavelength) light of 25.4 W m^-2 for 5 days. As a result, when kale plants with thickened leaves from treatment with high CO₂ were exposed to UV-A, they had lower UV sensitivity than thinner leaves. The Fv/Fm (maximum quantum yield on photosystem II) in the leaves of kale exposed to UV-A in a low-concentration CO₂ environment decreased abruptly and significantly immediately after UV treatment, but not in kale leaves exposed to UV-A in a high-concentration CO₂ environment. The accumulation pattern of total phenolic content, antioxidant capacity and individual phenolic compounds varied according to leaf thickness. In conclusion, this experiment suggests that the UV intensity should vary based on the leaf thickness (age etc.) during UV treatment for phytochemical enhancement.