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Light plays an important role in influencing the nutritional quality of food crops, especially with regard to the health-promoting phytochemicals. However, its role in affecting the nutritional quality with regard to the essential nutrients is not well understood. In this study, the effects of preharvest UV-A treatment on the nutritional quality of lettuce (Lactuca sativa, cv. red-leaf ‘New Red Fire’ and green-leaf ‘Two Star’) in relation to the essential nutrients and health-promoting phytochemicals were explored. Lettuce plants were grown in a growth chamber and were subjected to supplemental UV-A LEDs (peak wavelength 375 nm) for a brief period (3–6 days) prior to harvest. UV-A LEDs were equipped with lenses to control the light dispersion. Many growth indices such as shoot fresh mass, leaf area, and leaf number were unaffected by supplemental UV-A in both varieties while shoot dry mass decreased in response to a 6-day UV-A treatment compared to the control. Leaf chlorophyll and carotenoid concentrations increased significantly in green-leaf lettuce after 3 or 6 days of UV-A treatment, but only after 3 days of UV-A treatment in red-leaf lettuce compared to the control. Leaf protein concentration increased significantly in both lettuce varieties along with a number of essential nutrients such as phosphorus, potassium, calcium, manganese, and sulfur in response to supplemental UV-A. Supplemental UV-A increased the accumulation of protein by approximately 48% in green-leaf lettuce and 31% in red-leaf lettuce compared to the control plants. Moreover, in addition to the above essential nutrients, green-leaf lettuce accumulated higher amounts of magnesium, copper, and zinc compared to the control plants, indicating that green-leaf lettuce was more responsive to preharvest supplemental UV-A treatment than red-leaf lettuce. However, the accumulation of total phenolic compounds and flavonoids in both varieties was lower under supplemental UV-A. Furthermore, the use of LED lenses did not have a consistent impact on most of the plant responses studied. Overall, the results indicate that a brief preharvest exposure of both red- and green-leaf lettuce varieties to UV-A increased their nutritional quality by enhancing the accumulation of protein and other major essential nutrients.

The objective of this study was to determine the efficiency of balloon flower sprout’s saponin production in a plant factory with artificial lighting (PFAL). Balloon flower has been traditionally used as herbal medicine and now, it is used as a medicinal plant as well as a functional food. It is important to establish the cultivation conditions for the stable production of high-quality balloon flower. Therefore, this study aimed to investigate the effects of culture systems and temperature conditions on the growth and saponin accumulation of balloon flower sprouts in controlled environment systems. One-year balloon flower roots were cultivated in soil and soilless culture systems at different temperature conditions (20, 25, and 30 °C) for 17 days. The results showed that the shoot fresh weight and shoot dry weight of the balloon flower sprouts grown in the soilless culture system at 25 °C were significantly increased by about 1.29 and 1.58 times, respectively, as compared with those of the sprouts grown in a soil culture system. Sprouts grown in the soilless culture system at 25 °C also recorded the highest root fresh weight, whereas there was no significant difference in root dry weight among the treatments. The plant height results showed an increased trend similar to that of the shoot fresh weight and shoot dry weight of the balloon flower sprouts. The concentrations of platycodin D3 (Pd-D3), polygalcin D (Pc-D), and total saponin in the shoot parts were highest in the soilless culture system at 20 and 25 °C. The root parts of sprouts grown in the soilless culture system at 30 °C also had higher deapioplatycodin D (Dpd-D) and total saponin concentrations. Overall, these results suggest that a soilless culture system with temperature conditions at 20 and 25 °C is suitable for improving the growth and saponin concentration of balloon flower cultivated in PFALs. Ultimately, our research should be a valuable resource for future research on the production of medicinal plants such as sprouts and should provide basic information to establish methods for enhancing the growth and bioactive compounds in balloon flower.

The low survival rates of in vitro-propagated plantlets under ex vitro conditions greatly inhibits the production of virus-free apple rootstock plantlets and necessitates tight control of ex vitro environments during plantlet acclimatization. Accordingly, this study investigated the effects of light intensity on the ex vitro acclimation of apple plantlets. In vitro-propagated ‘M9’ apple plantlets were acclimatized for 6 weeks under different light treatments: 60 μmol m−2 s−1 (L), 100 μmol m−2 s−1 (M), 140 μmol m−2 s−1 (H), 180 μmol m−2 s−1 (VH), 60 → 100 μmol m−2 s−1 at 2 weeks (L2M4) or 4 weeks (L4M2), 60 → 100 → 140 μmol m−2 s−1 (L2M2H2), and 60 → 140 μmol m−2 s−1 at 4 weeks (L4H2). Survival rate, maximum quantum yield of photosystem II (Fv/Fm), growth-related parameters, and photosynthetic rate were measured. The H and VH treatments yielded the lowest survival rates (78 and 71%, respectively), whereas the M treatment yielded the highest (95%). Meanwhile, the Fv/Fm ratio at 6 weeks after transplanting decreased with increasing light intensity at 4 and 5 weeks, whereas photosynthetic rate at 5 weeks after transplanting and stem diameter at 6 weeks after transplanting increased with increasing light intensity. Furthermore, the M treatment yielded greater relative growth rates than the other treatments at 2–4 weeks, and both the M and L2M2H2 treatments yielded significantly greater relative growth rates at 4–6 weeks. These results suggest that the M and L2M2H2 treatments are appropriate for the acclimatization of in vitro-propagated ‘M9’ apple plantlets.

This study aimed to explore the suitable light quality condition for ex vitro acclimation of M9 apple plantlets. Light quality treatments were set as followed, monochromatic LEDs (red (R), green (G), blue (B)) and polychromatic LEDs (R:B = 7:3, 8:2 and 9:1, R:G:B = 6:1:3, 7:1:2 and 8:1:1). Plant height of R, R9B1, and R8G1B1 treatments were significantly higher than the other treatments. The number of leaves and SPAD value of B were significantly higher than the other treatments. Root fresh weights of R9B1 and R7G1B2 treatments showed an increase of at least 1.7-times compared to R, G and R8B2. R8G1B1 accumulated higher starch contents than the other treatments. Photosynthetic rate of R9B1 and R8B2 were significantly higher than the other treatments. In terms of stomatal conductance and transpiration rate, treatments with high blue ratio such as B, R7B3 had higher values. Rubisco concentration was high in R and B among monochromatic treatments. In conclusion, red light was effective to increase photosynthetic rate and biomass and blue light increased chlorophyll content and stomatal conductance. Therefore, for R9B1 and R8G1B1, a mixture of high ratio of red light with a little blue light would be proper for the acclimation of in vitro-propagated apple rootstock M9 plantlets to an ex vitro environment.

The present study aimed to evaluate the effects of controlling the relative humidity (RH) and water content of the root-zone on the survival rate and growth of in vitro-propagated virus-free M9 apple plantlets in closed-type plant production systems. In the first experiment, three RH regimes were applied to pre-acclimated (PA) and non-PA apple plantlets for 6 weeks after transplantation. In the second experiment, the apple plantlets were transplanted into several growth media, including a mixture of peat moss and perlite (PP), rock wool (RW), and urethane sponge (SP), and in a deep flow technique (DFT) system for controlled root zone water content under controlled RH. In the first experiment, pre-acclimation improved the survival rate by preventing the loss of leaf water potential and promoting antioxidant capacity during the acclimation period. However, no clear difference was found among the three RH regimes. The antioxidant capacity was increased at 2 weeks after transplantation, followed by root initiation. The leaf water potential, which decreased continuously until 3 weeks after transplanting, tended to remain constant after root initiation. These results suggested that pre-acclimation is necessary for the survival of in vitro-propagated apple plantlets, and that the underdeveloped roots of apple plantlets have restricted water absorption under controlled RH. In the second experiment, the survival rate of plantlets grown in PP at 6 weeks after transplantation was only 70% accompanied by an increase in antioxidant capacity, whereas the survival rates of plantlets grown in RW, SP, DFT, and DFT-PP (replanted to PP from DFT 4 weeks after transplantation) were 98, 96, 93.8, and 93.8%, respectively. Most of the growth parameters of the plantlets grown in DFT were the highest among the growth media at 6 weeks after transplantation. The results of the second experiment implied that the application of DFT for in vitro-propagated apple plantlets can reduce the problems caused by poor root architecture during acclimation.

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 (Lactuca sativa 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 (PAL) and chalcone synthase (CHS) 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.

Short-term abiotic stress treatment before harvest can enhance the quality of horticultural crops cultivated in controlled environments. Here, we investigated the effects of combined chilling and UV-A treatment on the accumulation of phenolic compounds in kale (Brassica oleracea var. acephala). Five-week-old plants were subjected to combined treatments (10 &deg, C plus UV-A LED radiation at 30.3 W/m2) for 3-days, as well as single treatments (4 &deg, C, 10 &deg, C, or UV-A LED radiation). The growth parameters and photosynthetic rates of plants under the combined treatment were similar to those of the control, whereas UV-A treatment alone significantly increased these parameters. Maximum quantum yield (Fv/Fm) decreased and H2O2 increased in response to UV-A and combined treatments, implying that these treatments induced stress in kale. The total phenolic contents after 2- and 3-days of combined treatment and 1-day of recovery were 40%, 60%, and 50% higher than those of the control, respectively, and the phenylalanine ammonia-lyase activity also increased. Principal component analysis suggested that stress type and period determine the changes in secondary metabolites. Three days of combined stress treatment followed by 2-days of recovery increased the contents of quercetin derivatives. Therefore, combined chilling and UV-A treatment could improve the phenolic contents of leafy vegetables such as kale, without growth inhibition.

The objective of this study was to determine the effect of short-term low temperature on the concentration of phenolic antioxidant compounds in kale. For the low-temperature treatment, two kale cultivars (‘Manchoo Collard’ and ‘TBC’) grown for 3 weeks in a growth chamber were subjected to 4°C for 3 days, and subsequently allowed to recover for 2 days under normal growth conditions (20°C). Fresh and dry shoot and root weights, chlorophyll fluorescence (potential quantum yield in dark-adapted conditions), reactive oxygen species (O2 ·- and H2O2), total phenolic concentration, antioxidant capacity, individual phenolics, and phenylalanine ammonia-lyase (PAL) activity were measured before and after treatment. No significant difference was observed between the control and low-temperature treatments in the fresh or dry shoot or root weights of either cultivar. The Fv/Fm decreased during the low-temperature treatment in both cultivars, and O2 ·- and H2O2 were generated in ‘Manchoo Collard’ leaves treated with low temperature but not in ‘TBC’ leaves. ‘Manchoo Collard’ had a 15% higher total phenolic concentration than the control after 2 days of recovery, whereas that of ‘TBC’ was 16% lower than that of the control. Individual phenolic compounds, such as caffeic acid, ferulic acid, and kaempferol, exhibited a similar trend to the total phenolic concentration and antioxidant capacity. The increased PAL activity in ‘Manchoo Collard’ at low temperature was in accord with the total and individual phenolic content results. These results suggest that a short-term low temperature during cultivation of kale in a controlled environment is a potential strategy to increase the plant’s phenolic antioxidant compound content.