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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.

We evaluated the effect of a newly-developed nutrient solution of red perilla (NSP) with various electrical conductivity (EC) levels on plant growth, mineral content, and bioactive compounds. Four-week-old seedlings were grown in greenhouse nutrient solution as control (CT) (EC 1–3 dS m−1) or NSP (EC 1–6 dS m−1). NSP 1 dS m−1 induced better growth characteristics, whereas higher EC levels inhibited plant growth. Most of the macro-elements contents significantly decreased under NSP 6 dS m−1, whereas the micro-elements contents fluctuated according to EC levels. Total phenolic concentration in NSP was lower than that in CT, and total phenolic content was highest under NSP 1 dS m−1. Total anthocyanin and antioxidant concentrations and contents increased at lower EC levels. Rosmarinic and caffeic acids concentrations increased at higher EC levels, whereas there were no significant differences in these compound contents among the EC levels. No difference in perillaldehyde concentration was observed, whereas the content was higher at lower EC levels. Overall, these results suggest that NSP 1 dS m−1 is suitable for cultivating red perilla in plant factories.

This study aimed to evaluate the effect of the red (R)-to-blue (B) ratio of light on the growth and phenolic compounds of Crepidiastrum denticulatum under a phytochrome photostationary state (PSS) for growth in a plant factory with artificial light (PFAL) using light-emitting diodes (LEDs). Three-week-old C. denticulatum seedlings were transplanted into a PFAL where the air temperature, relative humidity, CO2 concentration, and light period were set at 20 °C, 60%, 1000 μmol·mol−1, and 16 h, respectively. Three controls were used with different ratios of R to B light without supplemental FR light: 8:2, 7:3, and 6:4 (based on chip number; 130 µmol·m−2·s−1 photosynthetic photon flux density). For the treatments, the same R to B light ratios as in the controls were used but supplemented with FR light, plus a treatment with only R light supplemented with FR, set to a PSS of 0.71. Growth characteristics and total phenolic and individual phenolic contents were measured after a 6-week treatment. When the R light ratio increased, shoot dry weight, leaf length, leaf width, and leaf area increased regardless of supplemental FR light, and the R8B2 with FR light treatment was the most effective, with significantly higher values (1.6–2 times) than the control. FR irradiation did not have any negative effect on total phenolic content, chlorogenic acid, caffeic acid, and chicoric acid per unit dry weight (g); thus, the R8B2 with FR treatment had significantly higher total phenolic and individual phenolic contents per shoot (43% and 52–62%, respectively). Thus, supplemental lighting with FR LEDs was found to be effective to enhance the growth and bioactive compounds of C. denticulatum in a PFAL installed with a R and B lighting system, and the effectiveness could be changed by the RB ratio, with 8:2 considered the proper ratio.

This study aimed to investigate the effects of UV-A light-emitting diodes (LEDs) and lamps on the growth and bioactive compounds of ice plant (Mesembryanthemum crystallinum). Three-week-old seedlings were germinated and grown at 23 °C air temperature, 60% relative humidity, 1000 μmol mol−1 CO2, 200 μmol m−2 s−1 (white LEDs), and a photo-period of 12 h for 3 weeks in a plant factory with artificial lighting. Plants were supplementally irradiated with different peak wavelengths of UV-A LEDs (395, 385, 375, and 365 nm) of 30 W m−2 and UV-A lamps of 15.5 W m−2 continuously for 7 days. Treatment with 395, 385, and 375 nm increased shoot fresh and dry weights than the control at 5 and 7 days of treatment. Fv/Fm value was significantly decreased at 12 h of all UV-A treatments and consistently showed lower levels compared to the control during the entire period. The photosynthetic rates of the 395 and 385 nm treatments were significantly higher than those of the other treatments. UV-A treatment enhanced total phenolic content and antioxidant capacity compared to those of the control after 3 days of treatment. Phenylalanine ammonia-lyase activity was also increased by UV-A light exposure. The content of pinitol, myo-inositol, and sucrose was increased by UV-A radiation, and the highest values were observed in the 395 nm treatment at 5 and 7 days of treatment. Our findings suggest that supplemental radiation of UV-A with a peak wavelength near 400 nm could increase the shoot biomass and antioxidant phenolics and sugar alcohols in ice plants.

Ultraviolet-B (UV-B) acts as a regulatory stimulus, inducing the dose-dependent biosynthesis of phenolic compounds such as flavonoids at the leaf level. However, the heterogeneity of biosynthesis activation generated within a whole plant is not fully understood until now and cannot be interpreted without quantification of UV-B radiation interception. In this study, we analyzed the spatial UV-B radiation interception of kales (Brassica oleracea L. var. Acephala) grown under supplemental UV-B LED using ray-tracing simulation with 3-dimension-scanned models and leaf optical properties. The UV-B-induced phenolic compounds and flavonoids accumulated more, with higher UV-B interception and younger leaves. To distinguish the effects of UV-B energy and leaf developmental age, the contents were regressed separately and simultaneously. The effect of intercepted UV-B on flavonoid content was 4.9-fold that of leaf age, but the effects on phenolic compound biosynthesis were similar. This study confirmed the feasibility and relevance of UV-B radiation interception analysis and paves the way to explore the physical and physiological base determining the intraindividual distribution of phenolic compound in controlled environments.

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 effects of substrate water content on the growth and content of bioactive compounds in Crepidiastrum denticulatum were evaluated. Three-week-old seedlings were subjected to four levels of substrate water content (20%, 30%, 45% and 60%) and maintained for 5 weeks. Growth parameters at 5 weeks of transplanting were significantly higher with the 45% substrate water content treatment than with the other treatments. In addition, photosynthetic rate, stomatal conductance and transpiration rate increased significantly and the highest sap flow rate during the day was observed in 45% substrate water content. Total phenolic content and antioxidant capacity per shoot increased significantly with substrate water content, increasing from 20% to 45% and decreased again at 60%. Antioxidant capacity and total hydroxycinnamic acids (HCAs) content per unit dry weight of plants under the 60% treatment were significantly higher than those under the 45% treatment, however, their content per shoot was the highest under the 45% treatment. Thus, 45% substrate water content is a suitable condition for the growth of C. denticulatum and had positive effects on phenolic content, antioxidant capacity, and HCAs content. These results could be useful for the mass production of high-quality C. denticulatum in greenhouses or plant factories capable of controlling the water content of the root zone.

High-energy ultraviolet (UV) light is an environmental stress that can be used to stimulate the biosynthesis of bioactive compounds in plants. This study aimed to comparatively determine the effects of UV-A, UV-B, and UV-C lamps or light-emitting diodes (LEDs) on the growth of dropwort (Oenanthe stolonifera) plants, and their contents of bioactive compounds. Dropwort seedlings with 2–3 offshoots were transplanted in a plant factory equipped with white LED and deep flow technique systems, and cultivated under standard growth conditions for 36 days. Thereafter, the dropwort plants were supplementally exposed to one of five UV treatments with energy equivalent to 10 W m−2: UV-C lamps for 2 days, UV-B lamps for 3 days, and UV-A lamps and LEDs with 370 nm or 385 nm peak wavelengths for 14 days. The variable fluorescence (Fv) to maximum fluorescence (Fm) ratio (Fv/Fm) of dropwort leaves began to significantly decrease 3 h after exposure to UV-C, and 6 h after UV-B exposure. Fluorescence in UV-C and UV-B-treated plants was lower than in control and UV-A-treated plants during the entire period of UV irradiation. The fresh weight of the shoots of plants treated with UV was not significantly different to those of the control plants during the entire UV irradiation period. The total phenolic content of dropwort shoots exposed to UV-A and UV-B treatments significantly increased compared to that of the control 1 day after treatment. The total phenolic content was highest in plants treated with the 370 nm UV-A LED, and this was significantly higher (33%) than the control. Plants treated with the 385 nm UV-A LED on day 3 of treatment had the highest total phenolic content compared to the other treatments. A similar trend was observed in contents of flavonoids and persicarin. UV light induced higher anthocyanin content than the control. The activity of phenylalanine ammonia-lyase after UV treatments was significantly higher than the control, supporting the findings of our bioactive compound assays. In conclusion, the results of this study suggest that irradiating vegetables with UV-A LEDs would be useful in plant factories with artificial light for improving vegetable quality without inhibiting growth.

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.

In the present study, the effect of light quality on endoreduplication and growth in Phalaenopsis ‘Spring Dancer’ plantlets was studied. The response of protocorm-like body (PLB)-derived plantlets subjected to monochromatic red (R60), blue (B60), and various combinations of both lights was investigated. Flow cytometry was used to investigate the effect of light on endocycle and growth, cell division, and endopolyploidy levels. In addition, the activities of stress-related enzymes such as catalase (CAT) and peroxidase (POD) were analyzed from leaves and roots. After 8 weeks, the leaf area of plants grown under monochromatic R60 and B60 light was found to be higher than that of plants grown under other wavelengths of light, except the control plants (fluorescent light). These results revealed monochrome blue (B60) light increased the ratio of endoreduplicated cells (4C–8C). CAT activity was highest in leaves grown under R60; however, the oxidized phenol concentration in the culture medium was lowest under R60 while it was the highest under B60 and fluorescent light (F). This indicates that plantlets were less stressed under R60 than B60 or F. The results of this study reveal that stress induced by monochromatic light stimulates endopolyploidy in leaves, which may subsequently increase Phalaenopsis leaf size.

The medicinal plant, coastal glehnia (Glehnia littoralis F. Schmidt ex Miq.), belongs to the Apiaceae, which is known to exhibit morpho-physiological seed dormancy (MPD). In this study, we aimed to determine the dormancy type of this plant, along with the conditions for breaking dormancy, and how to increase its germination rate for mass production. Initially, the seeds of coastal glehnia had undeveloped embryos, which gradually developed following cold (5 °C) stratification over eight weeks. The embryo to seed (E:S) ratio increased to 66.7%, confirming that the seeds had the MPD type. Coastal glehnia seeds with pericarp did not show inhibited water uptake, and the germination inhibitory chemicals were not detected. However, removal of the pericarp improved the final germination percentage, germination speed, and T50 of coastal glehnia seeds compared with those of seeds with pericarp at 20 °C, which showed the highest value compared with other temperature treatments. Thus, cold stratification at 5 °C for eight weeks and removing the pericarp of germinating seeds maintained at 20 °C is efficient ways to break dormancy and improve the germination rate for the mass production of coastal glehnia.

The aim of this study was to determine the effect of irradiation of various spectrums generated by light-emitting diodes (LEDs) on the growth and accumulation of bioactive compounds in dropwort (Oenanthe stolonifera). Dropwort plants with 2-3 offshoots were grown under three monochromatic LEDs: red (R; 654 nm), blue (B; 456 nm), and green (G; 518 nm), thirteen combinations of R and B (R:B = 9:1, 8:2, 7:3, and 6:4), RB with G (R:G:B = 9:1:0, 8:1:1, 7:1:2, and 6:1:3), and RB with white (W) (R:W:B = 8:2:0, 8:1:1, 7:2:1, 7:1:2, and 6:2:2) and fluorescent lamps (control) for 6 weeks. R LEDs improved growth characteristics, including plant height and fresh and dry weights of shoots. Combined LEDs with 70-80% red wavelength resulted in the highest values in fresh weight. The B LED treatment resulted in the highest total phenolic and anthocyanin content in dropwort leaves, which increased in the combined LEDs treatments as the proportion of blue wavelength increased. Further, the RWB treatments, regardless of the ratio, resulted in higher anthocyanin contents than that in the RB and RGB treatments. Persicarin content was also significantly higher in the B treatment than in the R and G treatments. However, compared to the RB treatments, persicarin content in the RGB and RWB treatments was decreased, on average, by 72 and 64%, respectively. We suggested that the light spectrum is closely related to the enhancement of growth and bioactive compounds. Our findings provide basic information for designing lighting systems in plant factories to improve the growth and bioactive compounds in dropwort.

The objective of this study was to determine the effects of mild water deficit on the contents of bioactive compounds in dropwort (Oenanthe stolonifera). Dropwort plantlets with 2-3 offshoots were transplanted into plastic pots containing horticultural growing medium. The plantlets were grown at 22°C under a relative humidity of 60%, photosynthetic photon flux density (PPFD) of 285 μmol·m -2 ·s -1, 12-hour light period, and CO2 concentration of 600 μmol·mol -1 and subirrigated with nutrient solution for 3 weeks after transplanting. To induce mild water deficit, we placed wick culture systems (4- and 6-cm long wicks) between the bottom of each pot and the water surface at 3 or 4 weeks after transplanting. The control plants were subirrigated at the pot bottom without wick treatment. The soil water content of plants under water-deficit averaged 45% lower than that of the control at 5 weeks after transplanting. Moreover, mild water-deficit treatment reduced the leaf water potential by 7-25% compared to the control. However, mild water-deficit treatment did not significantly affect the fresh or dry weights of dropwort shoots at 6 weeks after transplanting. All treatments significantly inhibited the photosynthetic rate at 5 weeks after transplanting. In particular, water-deficit treatment using a 6-cm long wick for 2 weeks resulted in a 16% lower photosynthetic rate than that of the control. The total phenolic content and antioxidant capacity of dropwort stems did not significantly differ between treatments. However, in the leaves, total phenolic content and antioxidant capacity of all plants subjected to water-deficit treatments averaged 43 and 64% higher, respectively, than those of the control. The total anthocyanin content in all treatment groups, except for treatment with a 4-cm wick at 4 weeks, was significantly higher than that of the control. These results suggest that dropwort plants subjected to mild water deficit effectively accumulate antioxidant phenolic compounds, including anthocyanins, which is more reminiscent of reddish, small dropwort plants that grow under limited water conditions than of water dropwort.

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.

Light-emitting diodes (LEDs) are currently undergoing rapid development as plant growth light sources in a plant factory with artificial lighting (PFAL). However, little is known about the effects of supplementary light and pulsed LEDs on plant growth, bioactive compound productions, and energy efficiency in lettuce. In this study, we aimed to determine the effects of supplementary white LEDs (study I) and pulsed LEDs (study II) on red leaf lettuce (Lactuca sativa L. ‘Sunmang’). In study I, six LED sources were used to determine the effects of supplementary white LEDs (RGB 7:1:1, 7:1:2, RWB 7:1:2, 7:2:1, 8:1:1, 8:2:0 [based on chip number] on lettuce). Fluorescent lamps were used as the control. In study II, pulsed RWB 7:2:1 LED treatments (30, 10, 1 kHz with a 50 or 75% duty ratio) were applied to lettuce. In study I, the application of red and blue fractions improved plant growth characteristics and the accumulation of antioxidant phenolic compounds, respectively. In addition, the application of green light increased plant growth, including the fresh and dry weights of shoots and roots, as well as leaf area. However, the substitution of green LEDs with white LEDs induced approximately 3.4-times higher light and energy use efficiency. In study II, the growth characteristics and photosynthesis of lettuce were affected by various combinations of duty ratio and frequency. In particular, biomass under a 1 kHz 75% duty ratio of pulsed LEDs was not significantly different from that of the control (continuous LEDs). Moreover, no significant difference in leaf photosynthetic rate was observed between any pulsed LED treatment utilizing a 75% duty ratio versus continuous LEDs. However, some pulsed LED treatments may potentially improve light and energy use efficiency compared to continuous LEDs. These results suggest that the fraction of red, blue, and green wavelengths of LEDs is an important factor for plant growth and the biosynthesis of bioactive compounds in lettuce and that supplementary white LEDs (based on a combination of red and blue LEDs) might be more suitable as a commercial lighting source than green LEDs. In addition, the use of suitable pulses of LEDs might save energy while inducing plant growth similar to that under continuous LEDs. Our findings provide important basic information for designing optimal light sources for use in a PFAL.

Adenophora triphylla var. japonica Hara is a highly valued medicinal plant that is used to treat or prevent bronchitis, cough, cancer, and obesity. However, there has been no study on the production of Adenophora triphylla var. japonica Hara seedlings in a closed-type plant production system (CPPS). This study was conducted to examine the growth characteristics of Adenophora triphylla var. japonica Hara seedlings as affected by different growing media. The seeds were sown on a 128-cell plug tray filled with urethane sponges (US), LC grow foam (LC), rockwool (RW), or terra-plugs (TP). The seedlings were cultured for a duration of 54 days under temperature 25 &plusmn, 1&deg, C, a photoperiod of 12/12 h (light/dark), and light intensity of 180 &micro, mol&middot, m&minus, 2&middot, s&minus, 1 photosynthetic photon flux density provided by RB LEDs (red:blue = 8:2) in a closed-type plant production system (CPPS). The germination rate of Adenophora triphylla var. japonica Hara was significantly highest in the TP. Also, seedling shoot growth indicators of plant height, leaf length, leaf width, number of leaves, fresh weight (FW), and dry weight (DW) of the shoot, and leaf area were markedly the greatest in the TP and the lowest in the US. The SPAD (soil-plant analysis development) value was higher in the TP and US than in the LC or RW. In addition, the seedling root growth characteristics of total root length, root surface area, root volume, and number of root tips were significantly greatest in the TP. Moreover, the maximum root diameter, FW and DW of roots were the greatest in the TP. In conclusion, the results suggest that TP are viable for the growth development of Adenophora triphylla var. japonica Hara seedlings.

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 aim of this study was to determine the influence of two types of UV-A LEDs on the growth and accumulation of phytochemicals in kale (Brassica oleracea var. acephala). Fourteen-day-old kale seedlings were transferred to a growth chamber and cultivated for 3 weeks. The kale plants were subsequently subjected to two types of UV-A LEDs (370 and 385 nm) of 30 W/m2 for 5 days. Growth characteristics were all significantly increased in plants exposed to UV-A LEDs, especially at the 385 nm level, for which dry weight of shoots and roots were significantly increased by 2.22 and 2.5 times, respectively, at 5 days of treatment. Maximum quantum efficiency of photosystem II photochemistry (Fv/Fm ratio) began to decrease after 3 h of treatment compared to the control. The total phenolic content of plants exposed to the two types of UV-A LEDs increased by 25% at 370 nm and 42% at 385 nm at 5 days of treatment, and antioxidant capacity also increased. The two types of UV-A LEDs also induced increasing contents of caffeic acid, ferulic acid, and kaempferol. The reactive oxygen species (ROS) temporarily increased in plants exposed to the two types of UV-A LEDs after 3 h of treatment. Moreover, transcript levels of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), and flavanone 3-hydroxylase (F3H) genes and PAL enzyme activity were higher in plants treated with UV-A LEDs. Our results suggested that short-term UV-A LEDs were effective in increasing growth and improving antioxidant phenolic compounds in kale, thereby representing a potentially effective strategy for enhancing the production of phytochemicals.

This study investigated growth and ginsenosides content of ginseng sprouts under various light spectra. One-year-old ginseng seedlings were cultivated under various light treatments including: monochromatic (red (R), green (G), and blue (B)), various RB and RGB combinations, white (fluorescent lamps (FL) and natural white (NW)), and supplemental far red (FR). R and high R ratio increased growth characteristics of ginseng sprouts (excepted for root dry weight). The replacement of G for B in RGB group and W group did not increase the growth, and supplemental FR increased shoot and root fresh weights, total fresh weight, and leaf area. R had 1.5 times higher photosynthetic rate compared to B and G, and R8G1B1 and R9G1B0 showed the highest values in RGB group, whereas the RB, W, and FR groups did not enhance photosynthetic rate. B and high B ratio increased shoot saponin and ginsenosides, total saponin and ginsenosides contents. Total saponin content in shoot was 4.4 times higher than that in root. The supplemental FR enhanced both total saponin and ginsenosides contents. In conclusion, NW + FR showed the highest total fresh weight, saponin and ginsenosides contents among all treatments, suggesting that supplementation of FR has a positive effect on ginseng sprouts grown in plant factories.

This study aims to determine the effect of different CO2 concentrations and light intensities on the growth, photosynthetic rate, and bioactive compound content of Glehnia littoralis Fr. Schmidt ex Miquel in a closed-type plant production system (CPPS). The plants were transplanted into a deep floating technique system with recycling nutrient solution (EC 1.0 dS&middot, m-1 and pH 6.5) and cultured for 96 days under a temperature of 20 &plusmn, 1 &deg, C, a photoperiod of 12/12 h (light/dark), and RGB LEDs (red:green:blue = 7:1:2) in a CPPS. The experimental treatments were set to 500 or 1500 &micro, mol∙mol&minus, 1 CO2 concentrations in combination with one of the three light intensities: 100, 200, or 300 &micro, mol∙m&minus, 2∙s&minus, 1 photosynthetic photon flux density (PPFD). The petiole length of G. littoralis was the longest in the 500 &micro, 1 CO2 concentration with the 100 &micro, 1 PPFD. The fresh weight (FW) and dry weight (DW) of shoots and roots were the heaviest in the 300 &micro, 1 PPFD regardless of the CO2 concentration. Higher CO2 concentrations and light intensities produced the greatest photosynthetic rates. However, the SPAD value was not significantly different between the treatments. Higher light intensities produced greater content per biomass of chlorogenic acid and total saponin, although the concentration per DW or FW was not significantly different between treatments. The first and second harvest yields were the greatest in the 300 &micro, 1 PPFD, regardless of the CO2 concentration. These results show that the 300 &micro, 1 PPFD enhanced the growth, photosynthetic rate, and bioactive compound accumulation of G. littoralis, regardless of the CO2 concentration in a CPPS.

The medicinal plant Crepidiastrum denticulatum, which is found throughout East Asia, contains various health-promoting phytochemicals. The aim of this study was to evaluate the effects of a newly developed nutrient solution (referred to as NSC) on the growth of this plant and to determine the proper EC level of NSC for stable phytochemical production in plant factories. Three-week-old seedlings were transplanted to a wick culture system supplied with Hoagland solution (EC 1.0 dS·m -1) as a control or with five different concentrations of NSC (EC 0.5, 1.0, 1.5, 2.0, and 2.5 dS·m -1). We grew the plants under normal conditions (20°C, 310 ± 10 µmol·m -2·s -1 PPF, CO2 1,000 µmol·mol -1, and a 16 hours photoperiod) for 6 weeks and evaluated their photosynthetic rates and growth characteristics, such as the fresh and dry weights of shoots and roots, leaf area, number of leaves, and S/R ratios, at 6 weeks after transplanting. We also measured the total phenolic content, antioxidant capacity, and chicoric acid content each week for 6 weeks after transplanting. The fresh weights of shoots and roots, leaf area, and number of leaves significantly increased in plants supplied with 2.0 and 2.5 dS·m -1 NSC compared with the control, while the photosynthetic rate did not change under different concentrations of NSC. The total phenolic content and antioxidant capacity per shoot significantly increased with increasing in EC level of NSC; this trend became more pronounced over time. Moreover, the chicoric acid content significantly increased during growth up to 6 weeks after transplanting. These results suggest that NSC increases the biomass of C. denticulatum and that an EC level of 2.0 or 2.5 dS·m -1 is proper for accumulating high levels of phytochemicals, such as chicoric acid, in C. denticulatum grown in plant factories.

Iron (Fe) is essential for many vital processes in plants, including chlorophyll biosynthesis, DNA synthesis, nitrogen reduction, and photosynthetic electron transfer. However, free Fe ions also participate in the Fenton reaction, which generates reactive oxygen species that induce oxidative stress, leading to lipid peroxidation, protein oxidation, and DNA mutation. Accordingly, plants have developed strategies to prevent roots from absorbing excess Fe. Here, we investigated Fe homeostasis in hydroponically grown spinach and kale under various Fe concentrations (5-800 µM), as well as the resulting changes in bioactive compound levels. Spinach and kale Fe contents did not increase under Fe concentrations in the nutrient solution of up to 200 µM. When spinach plants (grown in nutrient solution containing 2 µM Fe-EDTA) were transferred to 50 µM Fe-EDTA, ferric-chelate reductase activity in roots rapidly decreased within 24 hours. In kale, ferric-chelate reductase activity also significantly decreased with increasing Fe-EDTA concentration. As Fe did not accumulate in spinach plants, no significant differences in plant growth were observed. However, in kale, root growth was slightly suppressed by high Fe (100-200 µM) levels in the rhizosphere. Comparisons to other studies suggest that variations in phenolic and flavonoid contents are dependent on plant species, but overall, Fe treatment did not result in a significant increase in these compounds in spinach or kale. Our results suggest that in spinach and kale roots, the regulation of Fe contents by ferric-chelate reductase is responsible for maintaining Fe homeostasis.

The aim of this study was to analyze the growth and bioactive compounds of lettuce in response to far-red LED light supplemented with a combination of red and blue LED light. Sixteen-day-old red leaf lettuce seedlings were transplanted to a growth chamber equipped with red, blue, and far-red LEDs. After setting the ratio of blue (B) to red (R) LEDs to 2:8, the ratio of R to far-red (FR) LEDs was adjusted to 0.7, 1.2, 4.1, or 8.6 (B+R/FR 0.7, 1.2, 4.1, or 8.6). Additionally, plants were irradiated with combined B and R LEDs (B+R) and fluorescent lamps (control) for 24 days. Growth characteristics including cell division rate, epidermal cell density and thickness, and antioxidant phenolic compounds were measured. Supplementation with FR LED light improved shoot and root growth compared to plants under B+R and control treatment. B+R/FR 1.2 treatment resulted in the highest shoot fresh weight and leaf area on day 24 of treatment. Obvious activation of the G2M phase was not observed in plants under far-red treatment, and most far-red treatments besides B+R/FR 4.1 increased the epidermal cell size. Plants treated with B+R/FR ratios of only 0.7 and 1.2 had significantly higher total phenolic levels, antioxidant activity, chlorogenic acid contents, and caffeic acid contents per plant than the control. These results suggest that supplementing the existing visual light spectrum, such as red and blue light, with far-red LEDs improves lettuce growth and bioactive compound content in a closed-type plant production system.

Ultraviolet B (UV-B) light, as a physical elicitor, can promote the secondary metabolites biosynthesis in plants. We investigated effects of different energy levels of UV-B radiation on growth and bioactive compounds of Crepidiastrum denticulatum. Three-week-old seedlings were grown in a plant factory for 5 weeks. Plants were subjected to different levels of UV-B (0, 0.1, 0.25, 0.5, 1.0, and 1.25 W m&minus, 2), 6 h a day for 6 days. All UV-B treatments had no negative effect on the shoot dry weight, however, relatively high energy treatments (1.0 and 1.25 W m&minus, 2) inhibited the shoot fresh weight. UV-B light of 0.1, 0.25, and 0.5 W m&minus, 2 did not affect total chlorophyll and H2O2 contents, however, they increased total carotenoid content. On 4 days, 0.25 W m&minus, 2 treatment increased antioxidant capacity, total hydroxycinnamic acids (HCAs) content, and several sesquiterpenes. Treatments with 1.0 and 1.25 W m&minus, 2 increased total carotenoid, total HCAs, and H2O2 contents, and destroyed chlorophyll pigments, reducing maximum quantum yield of photosystem II and causing visible damage to leaves. Partial least squares discrimination analysis (PLS-DA) showed that secondary metabolites were distinguishably changed according to energy levels of UV-B. The potential of 0.25 W m&minus, 2 UV-B for the efficient production of bioactive compounds without growth inhibition in C. denticulatum was identified.

Crepidiastrum denticulatum (Korean common name: i-go-deul-ppae-gi) is a valuable medicinal plant used in the pharmaceutical industry and as a raw material of functional foods. In this study, we investigated the effect of light quality on C. denticulatum growth, with the goal of improving the species’ biomass and bioactive compound content when grown in plant factories with artificial lighting. Three-week-old seedlings were grown for 6 weeks in a plant factory under fluorescent lamps (control) and various sets of light-emitting diodes (LEDs): three monochromatic [red (R), green (G), and blue (B)], several dichromatic RB with different ratios of R and B [R:B = 6:4 (R6B4), 7:3 (R7B3), 8:2 (R8B2), and 9:1 (R9B1)], and several trichromatic RGB [R:G:B = 5:1:4 (R5G1B4), 6:1:3 (R6G1B3), 7:1:2 (R7G1B2), 8:1:1 (R8G1B1), and 9:1:0 (R9G1B0)]. Shoot biomass (fresh weight), leaf area, leaf shape index, and water content of the shoot were significantly higher in the RGB group than in the monochromatic and RB groups. Increasing the percentage of R light improved shoot growth in the presence of G light, as in the RGB group, and this was accompanied by a high photosynthetic rate, light absorbance rate, and electron transport rate. The contents of total phenolics and hydroxycinnamic acids per unit dry weight did not differ between plants subjected to the different light quality treatments, and the contents per shoot were thus positively associated with shoot biomass. Overall, R8G1B1 was the most effective treatment for increasing shoot biomass and the accumulation of bioactive compounds; the shoot fresh weight and total hydroxycinnamic content of R8G1B1 were significantly higher, by 50 % and 60 %, respectively, than those of the control. Thus, light quality affects the biosynthesis of bioactive compounds and the shoot biomass of C. denticulatum.