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UV-B radiation and high temperature have detrimental effects on plant physiological and biochemical processes. The use of bacterial inoculants for stress alleviation has been regarded as a sustainable and eco-friendly approach. Hence, this study was conducted to evaluate the ability of 1-aminocyclopropane-1-caboxylate (ACC) deaminase-producing Brevibacterium linens RS16 in enhancing stress tolerance in rice against combined UV-B radiation and heat stresses. A combination of 0.5 Wm−2 UV-B radiation and 40 °C of temperature were imposed on rice plants for 5 days. The plants imposed with combined stress had shown significantly higher ethylene emissions compared to the plants grown under normal conditions. In addition, the stress imposition had shown negative effects on the photosynthetic traits, biomass, and genetic material of rice plants. The inoculation of bacteria had shown a 26.5% and 31.8% decrease in ethylene emissions at 3 and 4 days of stress imposition compared to the non-inoculated plants. Additionally, bacterial inoculation had also enhanced plant biomass and photosynthetic traits, and had proved to be effective in restricting DNA damage under stress conditions. Taken together, the current study has shown the effective strategy of enhancing stress tolerance against the interactive effects of UV-B radiation and heat stresses by regulation of ethylene emissions through inoculating ACC deaminase-producing bacteria.

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.

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.

Background Light-emitting diodes (LEDs) are widely used in closed-type plant production systems to improve biomass and accumulate bioactive compounds in plants. Perilla has been commonly used as herbal medicine because of its health-promoting effects. This study aimed to investigate the physiological and biochemical responses of green and red perilla under various visible-light spectra. Results Results showed that red (R) LEDs improved fresh weights of shoots and roots, plant height, internode length, node number and leaf area, as well as photosynthetic rate of green and red perilla plants compared to blue (B) LEDs and RB combined LEDs. Meanwhile, B resulted in higher stomatal conductance, transpiration rate and Fv/Fm compared to R. Supplementation of green (G) and far-red (FR) did not enhance perilla growth. Reduction or absence of B decreased leaf thickness, adaxial and abaxial epidermis, and palisade and spongy mesophyll. Total phenolic content, antioxidant capacity, rosmarinic acid content and caffeic acid content of green perilla were higher under R, R8B2 and RGB + FR, while greater values were obtained in red perilla under R. Accumulation of perillaldehyde, luteolin and apigenin presented different trends from those of rosmarinic and caffeic acids in both cultivars. Conclusions Growth and accumulation of bioactive compounds in green perilla were greater than in red perilla under similar light quality, and R LEDs or a higher R ratio in combination treatments were suitable for cultivating high-quality green and red perilla plants in closed-type plant factories. © 2020 Society of Chemical Industry.

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.

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 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 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.

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.

This study was conducted to determine the effects of silver thiosulfate (STS) and 1-methylcyclopropene (1-MCP) on flower opening and lifespan of potted Kalanchoe blossfeldiana ‘Oriba’ for exportation. Ethylene inhibitors, STS and 1-MCP were applied to the kalanchoe plants prior to their export to Japan. STS 0.5 mM with 1% Tween 20 surfactant was directly sprayed (20 ㎖ per plant) to leaves, buds, and flowers and 1-MCP 100 nL?l?¹ was injected into sealed glass chambers containing kalanchoe plants, which were placed on the chambers for 6 hours. After transport to Japan, the plants were immediately transferred to a simulated retail condition room (80 μ㏖ㆍ?²ㆍs?¹ for 12 hours of photoperiod at 22℃ and 64% RH) at Toyko University. The numbers of buds, open florets, and wilted florets in the middle inflorescence for each plant were counted right after export, 1 week after export, and 6 weeks after export. The percentages of open florets and wilted florets were calculated from the numbers. STS treatment resulted in 35% more open florets than the control and only 11% of wilted florets at 6 weeks after export to Japan which indicate the extension of lifespan of potted kalanchoe plants. Meanwhile, the plants exposed to 1-MCP before export did not show any significant differences in the numbers of buds and open florets and the percentages of open and wilted florets compared to control plants. In conclusion, STS 0.5 mM treatment strikingly induced better opening florets and lifespan of kalanchoe plants from 1 week to 6 weeks after export than control.

This study was conducted to determine the effects of UV-A and UV-B wavelengths on the growth and content of antioxidant phenolic compounds in sowthistle (Ixeris dentata Nakai), a medicinal plant, grown in a closed plant-production system. In study I, sowthistle plants were continuously exposed to UV-A light. In study II, two UV treatments [repeated UV-B (R): 4 h·d−1 for 6 days, gradual UV-B (G): from 1 to 7 h·d−1 for 6 days] were applied to the sowthistle plants. As a result, contents of total phenolics and antioxidants in UV-A-treated plants were significantly (50 and 30%, respectively) higher than those in the control plants after 3 d of UV treatment without growth inhibition. Moreover, plants continuously exposed to UV-A for 5 d had 50% higher total flavonoid content than the control. The phenylalanine ammonia-lyase (PAL) activity supported the accumulation of phytochemicals in plants exposed to UV-A. The UV-B (R) treatment led to a more rapid decrease in the chlorophyll fluorescence ratio than UV-B (G) treatment. The UV-B (R) or UV-B (G) treatment produced more total phenolics, flavonoids, and antioxidants, although both UV-B treatments significantly inhibited plant growth measured at 2 days after treatment. The UV irradiation also enhanced PAL activity at 2 and 3 days after treatment, suggesting biosynthetic activation of secondary metabolites. Therefore, application of UV-A or UV-B light can be used as a strategy to improve antioxidant phenolic compounds of sowthistle plants grown in closed plant production systems.

BACKGROUND The production of high-quality crops based on phytochemicals is a strategy for accelerating the practical use of plant factories. Previous studies have demonstrated that ultraviolet (UV) light is effective in improving phytochemical production. This study aimed to determine the effect of various UV wavelengths on growth and phenolic compound accumulation in lettuce (Lactuca sativa L.) grown in a closed-type plant production system. RESULTS Seven days, 1 day and 0.25 day were determined as the upper limit of the irradiation periods for UV-A, -B, and -C, respectively, in the lettuce based on physiological disorders and the fluorescence parameter Fv/Fm. Continuous UV-A treatment significantly induced the accumulation of phenolic compounds and antioxidants until 4 days of treatment without growth inhibition, consistent with an increase in phenylalanine ammonia lyase (PAL) gene expression and PAL activity. Repeated or gradual UV-B exposure yielded approximately 1.4–3.6 times more total phenolics and antioxidants, respectively, than the controls did 2 days after the treatments, although both treatments inhibited lettuce growth. Repeated UV-C exposure increased phenolics but severely inhibited the growth of lettuce plants. CONCLUSION Our data suggest that UV irradiation can improve the accumulation of phenolic compounds with antioxidant properties in lettuce cultivated in plant factories. © 2013 Society of Chemical Industry

As an artificial light source, light-emitting diode (LED) with a short wavelength range can be used in closed-type plant production systems. Among various wavelength ranges in visible light, individual light spectra induce distinguishing influences on plant growth and development. In this study, we determined the effects of monochromatic LEDs on leaf shape index, growth and the accumulation of phytochemicals in a red leaf lettuce ( Lactuca sativa L. ‘Sunmang’) and a green leaf lettuce ( Lactuca sativa L. ‘Grand rapid TBR’). Lettuce seedlings grown under normal grow ing conditions (20 ℃, fluorescent lamp + high pressure sodium lamp, 130 ± 5 µmol ･m -2 ･s -1 , 12 hours photoperiod) for 18 days were transferred into incubators at 20 ℃ equipped with various monochromatic LEDs (blue LED, 456 nm; green LED, 518 nm; red LED, 654 nm; white LED, 456 nm + 558 nm) under the same light intensity and photoperiod (130 ± 7 µmol ･m -2 ･s -1 , 12 hours photoperiod). Leaf leng th, leaf width, leaf area, fresh and dry weights of shoots and roots, shoot/root ratio, SPAD value, total phenolic concentration, antioxidant capacity, and the expression of a key gene involved in the biosynthesis of phenolic compounds, phenylalanine ammonia-lyase (PAL), were measured at 9 and 23 days after transplanting. The leaf shape indexes of both lettuce cultivars subjected to blue or white LEDs were similar with those of control during whole growth stage. However, red and green LEDs induced significantly higher leaf shape index than the other treatments. The green LED had a negative impact on the lettuce growth. Most of growth characteristics such as fresh and dry weights of shoots and leaf area were the highest in both cultivars subjected to red LED treatment. In case of red leaf lettuce plants, shoot fresh weight under red LED was 3.8 times higher than that under green LED at 23 days after transplanting. In contrast, the accumulation of chlorophyll, phenolics including antioxidants in lettuce plants showed an opposite trend compared with growth. SPAD value, total phenolic concentration, and antioxidant capacity of lettuce grown under blue LED were significantly higher than those under other LED treatments. In addition, PA L gene was remarkably activated by blue LED at 9 days after transplanting. Thus , this study suggested that the light quality using LEDs is a crucial factor for morphology, growth, and phytochemicals of two lettuce cultivars.

Chilling stress is a production constraint of tomato, a tropical origin, chilling-sensitive horticultural crop. The development of chilling tolerant tomato thus has significant potential to impact tomato production. Glutaredoxins (GRXs) are ubiquitous oxidoreductases, which utilize the reducing power of glutathione to reduce disulfide bonds of substrate proteins and maintain cellular redox homeostasis. Here, we report that tomato expressing Arabidopsis GRX gene AtGRXS17 conferred tolerance to chilling stress without adverse effects on growth and development. AtGRXS17-expressing tomato plants displayed lower ion leakage, higher maximal photochemical efficiency of photosystem II (Fv/Fm) and increased accumulation of soluble sugar compared with wild-type plants after the chilling stress challenge. Furthermore, chilling tolerance was correlated with increased antioxidant enzyme activities and reduced H2O2 accumulation. At the same time, temporal expression patterns of the endogenous C-repeat/DRE-binding factor 1 (SlCBF1) and CBF mediated-cold regulated genes were not altered in AtGRXS17-expressing plants when compared with wild-type plants, and proline concentrations remained unchanged relative to wild-type plants under chilling stress. Green fluorescent protein -AtGRXS17 fusion proteins, which were initially localized in the cytoplasm, migrated into the nucleus during chilling stress, reflecting a possible role of AtGRXS17 in nuclear signaling of chilling stress responses. Together, our findings demonstrate that genetically engineered tomato plants expressing AtGRXS17 can enhance chilling tolerance and suggest a genetic engineering strategy to improve chilling tolerance without yield penalty across different crop species.

Genotype along with growing and management conditions can affect the content and the composition of phytochemicals in plants. Two lettuce (Lactuca sativa L.) cultivars, ‘Baronet’ and ‘Red Sails,’ were grown in an open field and high tunnels to examine the effect of growing conditions on their phytochemical content. The total phenolic concentration and antioxidant capacity of lettuce increased in response to transplanting from greenhouse to both open field and high tunnels. However, the increase was much greater when seedlings were transplanted to the open field and was more than 4 fold over the pre-transplant stage. The concentrations of two major phenolic compounds, chicoric acid and chlorogenic acid, were about 2.5–5.5 times higher in both cultivars when grown in open field than in high tunnels. Also, growing lettuce in open field resulted in a greater activation of key genes (phenylalanine ammonia-lyase, L-galactose dehydrogenase and γ-tocopherol methyl transferase) involved in the biosynthesis of phenolic compounds, ascorbic acid and α-tocopherol. ‘Red Sails’ accumulated caffeic acid 4 times as much in open field as it did in high tunnels and overall contained higher amount of phenolic compounds, especially in open field, than did Baronet. Although lettuce plants grown in open field were richer in phytochemicals, a significant reduction in biomass accumulation occurred when the lettuce plants were grown in open field compared to high tunnels regardless of cultivar. These results show that growing conditions, in addition to genotype, can significantly affect the content of many phenolic compounds in lettuce and that growing lettuce under open field can have a positive impact on its health-promoting qualities.

BACKGROUND: Edible sprouts are thought to be rich in health-promoting phytochemicals that are known to prevent a number of chronic and degenerative diseases. In mature plants, environmental shocks have been used to enhance health-promoting phytochemicals. The primary objective of this study was to use environmental shocks involving high light and chilling in sprouts of alfalfa, broccoli and radish to improve their phenolic composition. RESULTS: Young sprouts had high total phenolic content and correspondingly high antioxidant capacity, both of which declined sharply with plant age. Exposure of sprouts to high light or chilling resulted in higher total phenolic content and antioxidant capacity compared with untreated controls. During recovery following shock treatments, high light produced a stronger response in increasing the levels of individual phenolic compounds. Alfalfa sprouts subjected to high light and chilling accumulated about 2.0 and 1.5 times significantly higher concentration of ferulic acid respectively, while high light induced 83% more sinapic acid in broccoli sprouts compared with untreated controls. Myricetin, while not detected in 5-day-old control or chilling-treated radish sprouts, accumulated in response to high light. Environmental shocks did not adversely affect the dry biomass accumulation. CONCLUSION: Environmental shocks involving high light and chilling enhanced the antioxidant phenolic content in sprouts of alfalfa, broccoli and radish, suggesting that this approach can be successfully used to enhance the health-promoting qualities of these sprouts. Copyright © 2009 Society of Chemical Industry

Plants typically respond to environmental stresses by inducing antioxidants as a defense mechanism. As a number of these are also phytochemicals with health-promoting qualities in the human diet, we have used mild environmental stresses to enhance the phytochemical content of lettuce, a common leafy vegetable. Five-week-old lettuce (Lactuca sativa L.) plants grown in growth chambers were exposed to mild stresses such as heat shock (40 � C for 10 min), chilling (4 � C for 1 d) or high light intensity (800 mmol m � 2 s �1 for 1 d). In response to these stresses, there was a two to threefold increase in the total phenolic content and a significant increase in the antioxidant capacity. The concentrations of two major phenolic compounds in lettuce, chicoric acid and chlorogenic acid, increased significantly in response to all the stresses. Quercetin-3-O-glucoside and luteolin-7-O-glucoside were not detected in the control plants, but showed marked accumulations following the stress treatments. The results suggest that certain phenolic compounds can be induced in lettuce by environmental stresses. Of all the stress treatments, high light produced the greatest accumulation of phenolic compounds, especially following the stress treatments during the recovery. In addition, key genes such as phenylalanine ammonia-lyase (PAL), L-galactose dehydrogenase (L-GalDH), and g-tocopherol methyltransferase (g-TMT) involved in the biosynthesis of phenolic compounds, ascorbic acid, and a-tocopherol, respectively, were rapidly activated by chilling stress while heat shock and high light did not appear to have an effect on the expression of PAL and g-TMT. However, L-GalDH was consistently activated in response to all the stresses. The results also show that these mild environmental stresses had no adverse effects on the overall growth of lettuce, suggesting that it is possible to use mild environmental stresses to successfully improve the phytochemical content and hence the health-promoting quality of lettuce with little or no adverse effect on its growth or yield. Published by Elsevier Masson SAS.