Light-emitting Diodes Light Treatments Research Articles

Effect of Light Spectrum on Gas Exchange, Growth and Biochemical Characteristics of Einkorn Seedlings

The use of Light Emitting Diode (LED) lights in microscale vegetable production is more and more widespread. In this context, the effect of light spectrum on photosynthesis, growth, shoot yield, pigment content, and nutritional status of einkorn seedlings (Triticum monococcum L. ssp. monococcum), germinated and grown in a nutrient solution, was investigated. Plants were subjected to six different LED light treatments, all having a photon flux density (PFD) of 200 μmol m−2 s−1. Two light treatments were monochromatic (red or blue), three dichromatic (blue and red in the proportion), and one of a wider spectrum (selected as a control). All the light treatments affected the morphological, biochemical, and nutritional status of einkorn seedlings. Overall, the dichromatic treatments were the most effective in stimulating biomass production, CO2 assimilation, and evapotranspiration, as well as contents in chlorophyll a and b and carotenoids, and additionally nitrogen, phosphorous, manganese, iron, and zinc. These results are of relevance for the beneficial effects of dichromatic LED treatments in maximizing einkorn shoot yield and nutritional values, and in limiting energy consumption in indoor cultivation.

Growth, pigment content, antioxidant activity, and phytoene desaturase gene expression in Caulerpa lentillifera grown under different combinations of blue and red light-emitting diodes

Light-emitting diodes (LEDs) have been developed as light sources for indoor algae cultivation. In this study, we determined the effects of blue and red light ratios on weight gain, pigment content, antioxidant activity, and phytoene desaturase (PDS) gene expression in Caulerpa lentillifera. Caulerpa lentillifera was grown under six LED light treatments: white (W), red (R, 660 nm, 100%), blue (B, 447 nm, 100%), 1B1R (50% blue + 50% red), 1B2R (33.3% blue + 66.7% red), and 1B5R (16.7% blue + 83.3% red). Our results showed that red light improved the weight gain percentage of C. lentillifera, whereas red light with a low proportion of blue light (1B5R, 16.7%; blue + 83.3% red) led to a significantly higher weight gain percentage and photosynthetic pigment (Chl a + Chl b) content than the other LED light treatments. Increasing the proportion of blue light negatively affected weight gain and the photosynthetic pigment contents. However, blue LED light induced significantly higher transcription of the PDS gene, which coincided with increased β-carotene accumulation and antioxidant activity in C. lentillifera. These results indicated that the ratio of blue to red light is important for the indoor cultivation of C. lentillifera, and 100 μmol photons m−2 s−1 of 1B5R LED light with a 12/12 h light-dark photoperiod resulted in good growth and development.

Changes in enzyme activities and amino acids and their relations with phenolic compounds contents in okra treated by LED lights of different colors

Light-emitting diodes (LEDs) of different wavelengths or colors (i.e., white, red, blue, and green) were used to treat postharvest okra, which is a rich source of phenolic compounds. Relationships between changes in the activities of key enzymes involving in the formation of phenolics (i.e., 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase, chorismate mutase, anthranilate synthase, and phenylalanine ammonia lyase) and their contents upon different LED light treatments were for the first time investigated and are fully discussed. The contents of three intermediate amino acids (i.e., phenylalanine, tyrosine, and tryptophan) that formed during light treatments were also measured to confirm the enzyme activities data. White and blue light treatments increased the content of phenolics in the treated okra, while red and green lights increased the formation of other compounds. These results could be well explained by the changing levels of the measured enzyme activities and amino acids contents.

Effects of Composite LED Light on Root Growth and Antioxidant Capacity of Cunninghamia lanceolata Tissue Culture Seedlings

We used the 12th generation of the Cunninghamia (C.) lanceolata tissue culture seedlings, and white light emitting diode (LED) light as control (CK). We applied five composite LED light treatments, red-blue 4:1, 8:1 (4R1B and 8R1B), red-blue-purple 8:1:1 (8R1B1P), and red-blue-purple-green 6:1:1:1, 8:1:1:1 (6R1B1P1G and 8R1B1P1G), to study the effects of light quality on root growth characteristics and antioxidant capacity of C. lanceolata tissue culture seedlings. The results showed that: (1) rooting rate, average root number, root length, root surface area, and root activity were higher with 6R1B1P1G and 8R1B1P1G treatments compared to 4R1B, 8R1B, 8R1B1P and CK treatments; and the root growth parameters under the 8R1B1P1G treatment were as high as 95.50% for rooting rate, 4.63 per plant of the average number of root, 5.95 cm root length, 1.92 cm2 surface area, and 145.56 ng/(g·h) root activity, respectively. (2) The composite lights of 4R1B, 8R1B, 8R1B1P, 6R1B1P1G, and 8R1B1P1G are beneficial for the accumulation of soluble sugar content (SSC) and soluble protein content (SPC), but not conducive for the increase of free proline content (FPC); the plants under 6R1B1P1G and 8R1B1P1G treatments had higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) activity and lower malondialdehyde (MDA), polyphenol oxidase (PPO) activity. (3) Redundancy analysis showed that POD activity positively correlated with root activity; SPC, SOD and CAT activities positively correlated with root growth parameters; while SSC, MDA content, APX and PPO activities negatively correlated with root growth parameters. These results suggest that the responses of root growth and antioxidant capacity of the C. lanceolata tissue culture seedlings to different light qualities vary. The relationship between root growth parameters and antioxidant capacity was closely related. Red-blue-purple-green was the most suitable composite light quality for root growth of C. lanceolata tissue culture seedlings, and 8:1:1:1 was the optimal ratio, under which the rooting rate, root activity and root growth of tissue culture seedlings peaked.

Supplemental LED lighting affects the dynamics of tomato fruit growth and composition

Understanding how greenhouse crops respond to supplemental lighting with light-emitting diodes (LEDs) compared with traditional lighting systems is essential to utilize the full potential of LEDs and their further adoption in energy efficient greenhouses. This study quantified the effects of supplemental lighting with high-pressure sodium (HPS) lamps and LED light on the dynamics of fruit growth and composition in tomato (Solanum lycopersicum L.). Two tomato genotypes (‘Foundation’ and ‘Progression’) were grown under daylight supplemented either with HPS (125 μmol m−2 s−1) combined with red/blue LED lighting (106 μmol m−2 s−1, HPS + LED light treatment) or red/blue LED light only (106 + 110 μmol m−2 s−1, LED + LED light treatment); and two genotypes (‘Foundation’ and ‘NUN09204’) under daylight supplemented either with red/blue LED light (200 μmol m−2 s−1, red/blue LED light treatment) or red/blue LED + far-red LED light (200 μmol m−2 s−1 + 40 μmol m−2 s−1, red/blue + far-red LED light treatment). Fresh weight and composition in glucose, fructose, sucrose, starch, citric acid and malic acid of tomato fruits at different stages of development were measured and analyzed in terms of three main underlying components: water dilution, dilution by soluble and storage compounds and metabolism. Growing fruits under the LED + LED compared to the HPS + LED light treatments increased average fruit fresh weight in all genotypes. The red/blue + far-red LED light treatment increased the production of soluble sugar, increased the dilution by soluble and storage compounds, and reduced water dilution leading to a strong increase in glucose, fructose and sucrose concentration in the pericarp. The LED + LED light treatment did not affect the metabolism of fruit biochemical compounds compared to the HPS + LED light treatments, but caused small changes in water dilution, which were reflected in the concentration of biochemical compounds. Dilution and metabolism were involved in genotypic differences in fruit composition. Our results show that altering the spectral composition of the supplemental light in energy efficient greenhouses can be done without an effect on fruit quality or even with an improvement of tomato fruit quality. Possible physiological processes underlying these light-induced changes in fruit biochemical compounds during fruit development in different genotypes were discussed.

A Systems Analysis With "Simplified Source-Sink Model" Reveals Metabolic Reprogramming in a Pair of Source-to-Sink Organs During Early Fruit Development in Tomato by LED Light Treatments.

Tomato (Solanum lycopersicum) is a model crop for studying development regulation and ripening in flesh fruits and vegetables. Supplementary light to maintain the optimal light environment can lead to the stable growth of tomatoes in greenhouses and areas without sufficient daily light integral. Technological advances in genome-wide molecular phenotyping have dramatically enhanced our understanding of metabolic shifts in the plant metabolism across tomato fruit development. However, comprehensive metabolic and transcriptional behaviors along the developmental process under supplementary light provided by light-emitting diodes (LEDs) remain to be fully elucidated. We present integrative omic approaches to identify the impact on the metabolism of a single tomato plant leaf exposed to monochromatic red LEDs of different intensities during the fruit development stage. Our special light delivery system, the “simplified source-sink model,” involves the exposure of a single leaf below the second truss to red LED light of different intensities. We evaluated fruit-size- and fruit-shape variations elicited by different light intensities. Our findings suggest that more than high-light treatment (500 μmol m-2 s-1) with the red LED light is required to accelerate fruit growth for 2 weeks after anthesis. To investigate transcriptomic and metabolomic changes in leaf- and fruit samples we used microarray-, RNA sequencing-, and gas chromatography-mass spectrometry techniques. We found that metabolic shifts in the carbohydrate metabolism and in several key pathways contributed to fruit development, including ripening and cell-wall modification. Our findings suggest that the proposed workflow aids in the identification of key metabolites in the central metabolism that respond to monochromatic red-LED treatment and contribute to increase the fruit size of tomato plants. This study expands our understanding of systems-level responses mediated by low-, appropriate-, and high levels of red light irradiation in the fruit growth of tomato plants.

The Management of Melasma on Skin Types V and VI Using Light Emitting Diode Treatment.

This study investigated light emitting diode (LED) treatment for patients with melasma on darker skin types. Melasma is a common disfiguring skin condition in women which is difficult to treat and is refractory. The cause of melasma remains unclear. In this study, 60 female participants aged between 25 and 60 years, who presented with melasma, were enrolled (n = 39.85). They were purposely assigned to two groups according to their skin types. Both groups received a total of 36 LED light treatments over a period of 9 months. Both subjective and objective results indicated a significant improvement of melasma. Statistical analyses revealed significant improvements in both groups. The results of this study suggest that LED is effective in managing melasma. These results will provide a basis for future therapeutic use of phototherapy to improve melasma.

Enhanced growth rate and ulvan yield of Ulva pertusa using light-emitting diodes (LEDs)

Light-emitting diode (LED) technology offers potential energy-efficient light sources for algal aquaculture. In this study, the growth rate and ulvan yield of Ulva pertusa used for broad commercial applications were enhanced in vitro. To investigate the response of Ulva to LEDs, algae were grown under white fluorescent, pure primary color LED, and mixed LED lights for 28 days. Ulva sp. under blue LED and white fluorescent light showed higher specific growth rate (SGR, 12% day−1) than other light sources, while the growth under mixed red-blue LED light was lower than that under white fluorescent lighting. Despite the differences in alga growth under LEDs and white fluorescent light, few differences are observed in N and P content among algae grown under any light source. U. pertusa showed tissue nitrogen and ulvan contents in the ranges of 4.4–6.7% and 20.4–25.1%, respectively, under all LED light treatments. The ulvan extracted from algae under blue LED showed high levels of antioxidant activity measured with 2,2-diphenylpicrylhydrazyl (DPPH) radical and hydrogen peroxide. Moreover, the ulvan obtained under different lights showed different monosaccharide compositions. Based on these results, LEDs should be considered as the main light sources for indoor seaweed cultivation.

Influence of blue/red vs. white LED light treatments on biomass, shoot morphology, and quality parameters of hydroponically grown kale

Abstract Solid-state light emitting diodes (LEDs) are emerging as an energy efficient alternative lighting source in controlled environments. The objective of this study was to examine the impact of sole-source LED lighting quality/duration on biomass, morphology, and nutritional quality of kale (Brassica oleracea var. acephala) in a controlled environment. ‘Premier’ kale seedlings were grown hydroponically using a 30 d production cycle. Experimental LED treatments included: 1) white LED for 37 d; 2) 5% B/95% R for 37 d; 3) 20%B/80%R for 30 d; 4) 20%B/80%R for 25 d; 5) 20%B/80%R for 20 d; and 6) 20%B/80%R for 15 d prior to harvest. Treatments were arranged in a randomized complete block design, and three complete experimental runs were conducted. Plant height (cm), leaf length and width (cm), shoot and root fresh mass (g) and dry mass (g) were collected at harvest. Kale shoot tissues were measured for nutritionally important pigments, glucosinolates, mineral elements, and soluble carbohydrates. All plants treated with 20%B/80%R lighting were shorter compared to the white (37 d) and 5%B/95%R (37 d) treatments, respectively. Chlorophyll fluorescence parameters were influenced by LED treatment, while maximum quantum yield (QYmax) was not. LED light treatment impacted kale zeaxanthin (P = 0.01), antheraxanthin (P = 0.01), fructose (P = 0.03), and potassium (P = 0.02). Data suggest that increasing blue light during production has limited impact on 37-d old hydroponic kale developmental and nutritional parameters over continuous white LED lighting.

Effect of Light-Emitting Diode (Led) Light on the Gene Expression Related With Ascorbate Biosynthesis and Metabolism in Broccoli Florets

Ascorbate is one of the most abundant soluble antioxidants in the plant. Multiple functions of ascorbate in photo protection have been proposed, including scavenging of reactive oxygen species generated by oxygen photoreduction and photorespiration. There is still unclear information relation to LED light with Ascorbate biosynthesis and metabolism, yellowing, chlorophyll content, and ethylene production in broccoli florets. The effect of light-emitting diodes (LED) light on ascorbate (AsA) biosynthesis and metabolism in broccoli (Brassica oleracea L. var. Italica) cultivar “Ryokurei” were studied using red (660 nm), blue (470 nm) and white LED lights as the light source and also no light treatment as the control. Gene expression involved in the biosynthesis and metabolism of AsA, AsA content, color, chlorophyll content and ethylene production rate on the postharvest broccoli were observed in 4 days. The result showed that after two days, red light treatment significantly (p < 0,05) delayed the decrease of ascorbate content. The result was supported by observations using Real-Time Quantitative RT-PCR showed that red light treatment can suppress mRNA level of BO-APX1, BO-APX2, and BO-sAPX on the third day. Observation of BO-GLDH mRNA level was increased in the third-day exposure of red LED light. Therefore red LED light showed up-regulated AsA biosynthesis transcriptional level. Enzymes which possibility responsible for AsA metabolism and biosynthesis in a row were Ascorbate Peroxide (APX) and L-Galactono-1,4-Lactone Dehydrogenase (GLDH). The regulation of this gene expression might contribute to the suppression of AsA reduction by red LED light treatment in broccoli. Red LED also showed suppression of yellowing and decline the chlorophyll content in postharvest broccoli florets. Keywords: ascorbate, LED; broccoli; gene expression; real-time quantitative RT-PCR.

Supplemental lighting with LEDs improves the biochemical composition of two Valerianella locusta (L.) cultivars

In recent years, light-emitting diodes (LEDs) have been introduced as a new source of supplemental lighting in winter greenhouse crop production to improve yield and quality. The aim of this study was to determine the effect of light supplementation with LEDs on the yield and the concentration of several health-promoting compounds in two cultivars of lamb’s lettuce (Valerianella locusta, L.), ‘Noordhollandse’ and ‘Hollandisher’ in a greenhouse cultivation in winter. Four different LED spectra used to extend the photoperiod (16 h day/8 h night) were tested: 10R:0B (100% red), 9R:1B (90% red, 10% blue), 8R:2B (80% red, 20% blue), and 7R:3B (70% red, 30% blue). The control plants were illuminated by high-pressure sodium (HPS) lamps. The photosynthetic photon flux density at the plant canopy level was approximately 200 μmol·m -2 ·s -1 in all treatments. The plants were harvested on the 45 th day of light treatment (60 days after sowing). In both cultivars, the 10R:0B LED light treatment resulted in the highest yield, but low concentrations of ascorbic acid, xantophylls, and phenolic compounds. Supplemental lighting with HPS lamps resulted in high concentrations of nitrate and carotenoids, but low fresh mass, ascorbic acid, and total phenols content. The addition of blue light in the spectrum increased antioxidant properties; however, certain effects were cultivar-dependent. High yields with the most satisfactory composition of soluble sugars, ascorbic acid, carotenoids, and polyphenols, as well as high antioxidant properties and reduced nitrate levels, in the leaves of the tested cultivars were obtained with 8R:2B LED lighting. Thus, supplemental lighting with 80% red and 20% blue light may be advantageous in greenhouse-cultivated V. locusta ‘Noordhollandse’ and ‘Hollandisher’ cultivars.

While continuous white LED lighting increases chlorophyll content (SPAD), green LED light reduces the infection rate of lettuce during storage and shelf-life conditions

The aim of this study is to prevent postharvest quality losses and enhance storage and shelf life of leaf lettuce using LED light treatments. For this purpose, four different colors of (white, green, red, and blue) LED light and darkness conditions were used. Lettuce was stored at a temperature of 5 °C ± 1 °C for 21 days, and after storage, it was kept at room temperature for 96 hr. This study demonstrated that white LED light showed up the best application in terms of maintaining green color, reducing chlorophyll degradation, and increasing the total soluble solid content of lettuce. While the weight loss was reduced by red LED light treatment, the green LED light was effective in reducing the decay rate of lettuce. It was concluded that white, red and green LED lighting treatments are useful for enhancing the storage life of leaf lettuce, whereas the blue LED light treatment showed negative effects. Practical applications Light-emitting diodes (LEDs) is used in horticultural production to increase yield by photosynthesis over decades. In postharvest storage stage, lighting of LED provided some advantages such as reducing of the growth of microorganism, especially citrus varieties. Leafy vegetables are identified susceptible because it contains large amount of water. Also they lose their green color very quickly after harvest. So, postharvest storage life of these type vegetable is quite short. As a result of the present study, chlorophyll (SPAD) content of leaf lettuce was increased by white LED light treatment both during storage and shelf life conditions. Therefore, by this technology, the shelf life of leaf lettuce would be increased by lighting of shelf in the supermarket by white LED, at least.

Effect of Various Monochromatic LED Light Colors on Performance, Blood Properties, Bone Mineral Density, and Meat Fatty Acid Composition of Ducks.

Two experiments determined the effects of various monochromatic light emitting diode (LED) light colors on performance, blood properties, bone mineral density, meat quality properties, and fatty acid composition of ducks. In Experiment 1, 720 1-d-old Cherry Valley ducklings were divided into four light treatments (six replicate pens/treatment; 30 ducks/pen) and were assigned to 1) yellow (Y), 2) green (G), 3) blue (B), or 4) control white (fluorescent lamps). In Experiment 2, six LED light treatments with four replicates were assigned as blue (PB), bright blue (BB), sky blue (SB), greenish blue (GB), green (PG), and fluorescent white as a control treatment. In Experiment 1, G light increased body weight and weight gain compared with the control and Y light during the first 21 d. During d 22–42, weight gain increased in the G and B treatments (P<0.034). Body weight and weight gain were increased under the G light treatment (P<0.036) in Experiment 2. Blood values were not influenced by the light treatments but serum cholesterol level decreased under the PB treatment (P<0.015) compared to PG treatment. Whole blood viscosity at a shear rate of 1 per second decreased significantly under the PG treatment than that of control W treatment. Ducks reared under GB and PG light had increased monounsaturated fatty acids and unsaturated fatty acids/saturated fatty acids by altering the fatty acid composition in muscle. These results suggest that monochromatic PG and GB light color increased growth performance, blood properties, and muscular fatty acid composition, while providing similar bone and meat properties in Cherry Valley ducks.

Interaction of light quality and fertility on biomass, shoot pigmentation and xanthophyll cycle flux in Chinese kale

Nutritionally important carotenoids in 21-day-old brassica microgreens increase following short and long-term exposure to narrow-band wavelengths from light-emitting diodes (LED). The present study aimed to measure the impact of: (1) fluorescent/incandescent light and different percentages of blue/red LED light and (2) different levels of nutrient fertility on biomass and pigment concentrations in 30-day-old 'Green Lance' Chinese kale (Brassica oleracea var. alboglabra). Kale plants were exposed to four light treatments and two fertility levels and were harvested 30 days after seeding and analyzed for nutritionally important shoot pigments. Kale under the fluorescent/incandescent light treatment had a significantly higher shoot fresh and dry mass. The shoot tissue concentrations of most pigment were significantly higher under blue/red LED light treatments. The higher fertility level resulted in higher concentrations for most pigments. Interestingly, the pool of xanthophyll cycle pigments and de-epoxidized xanthophylls was higher under all LED treatments. The results obtained in the present study support previous data demonstrating the stimulation of nutritionally important shoot tissue pigment concentrations following exposure to sole source blue/red LEDs compared to traditional lighting. Xanthophyll cycle flux was impacted by LEDs and this may support the role of zeaxanthin in blue light perception in leafy specialty crops. © 2016 Society of Chemical Industry.

Light quality impacts on growth, flowering, mineral uptake and petal pigmentation of marigold

Light quality has a significant impact on growth and development and time to flower in many plant species. Recently, the percentages of blue and red in narrow-band wavelengths of light from light-emitting diodes (LEDs) have been shown to impact mineral uptake, pigment development and the rate of growth and development of several plant species. The objective of this research was to evaluate the effects of light quality on shoot growth, flower development, mineral uptake and pigment content of marigold (Tagetes patula 'Safari Orange'). Plants were grown in 10-cm square pots in a greenhouse ebb and flood system with a complete nutrient solution. Plants received average day temperatures of 25°C and night temperatures of 16°C. The following light treatments were utilized in this study: 1) natural sunlight; 2) high-pressure sodium (HPS) lighting at 100 µmols m-2 s-1 intensity in addition to natural sunlight intensity; 3) LED lighting with blue and red wavelengths at 50% each and intensity at 100 µmols m-2 s-1 in addition to natural sunlight intensity; and 4) LED lighting with blue at 25% and red at 75% and intensity at 100 µmols m-2 s-1 in addition to natural sunlight intensity. Total shoot growth was twice as high in all supplemental light treatments compared to the natural sunlight treatment. Shoot growth was greater in the 25% blue/75% red LED treatment than in the HPS light treatment. The 50% blue/50% red LED treatment was not significantly different from the HPS light treatment. Plants in the 25% blue/75% red LED treatment had 15% more blooms than plants in the 50% blue/50% red LED treatment or the HPS light treatment. All supplemental light treatments produced plants with significantly more blooms than plants in the natural sunlight treatment. Plants in the LED light treatments had greater petal pigment content than plants in the natural sunlight treatment.

Blue and red LED lighting effects on plant biomass, stomatal conductance, and metabolite content in nine tomato genotypes

A collection of nine tomato genotypes was chosen based on their diversity, phylogeny, availability of genome information, and agronomic traits. The objective of the study was to characterize the effect of red and blue LED (light-emitting diode) lighting on physiological, morphological, developmental, and chemical parameters. Two LED light treatments were imposed: (1): 100% red and (2): 88% red/12% blue (peak emission at 662 and 456 nm for red and blue light, respectively). The combination of blue and red LED lighting increased total dry matter in seven of the nine genotypes compared to red. Upward or downward leaf curling was observed in all genotypes in the 100% red treatment. Stomatal conductance was not affected much by additional blue light, but blue light increased chlorophyll and flavonol contents in three genotypes. The exposure of tomato plants to a combination of red and blue LEDs alleviated leaf morphological abnormalities and enhanced plant biomass, and variably affected stomatal conductance and secondary metabolism compared to red light alone.

Effects of melatonin and green-wavelength LED light on the physiological stress and immunity of goldfish, Carassius auratus, exposed to high water temperature.

This study investigated the effects of increasing water temperature (22-30°C) on the physiological stress response and immunity of goldfish, Carassius auratus, and the ability of green light-emitting diode (LED) irradiation or melatonin injections to mitigate this temperature-induced stress. To evaluate the effects of either green-wavelength LED light or melatonin on stress in goldfish, we measured plasma triiodothyronine (T3), thyroxine (T4), and thyroid hormone receptor (TR) mRNA expression; plasma cortisol and glucose; and immunoglobulin M (IgM) and lysozyme mRNA expression. The thyroid hormone activities, TR mRNA expression, and plasma cortisol and glucose were higher in goldfish exposed to high-temperature water, but were lower after exposure to melatonin or green-wavelength LED light. Lysozyme mRNA expression and plasma IgM activity and protein expression were lower after exposure to high water temperatures and higher after melatonin or green-wavelength LED light treatments. Therefore, high water temperature induced stress and decreased immunity; however, green-wavelength LED light and melatonin treatments mitigated the effects of stress and enhanced immunity. The benefits of melatonin decreased with time, whereas those of green-wavelength LED treatment did not.

Continuous Light from Red, Blue, and Green Light-emitting Diodes Reduces Nitrate Content and Enhances Phytochemical Concentrations and Antioxidant Capacity in Lettuce

Light-emitting diodes (LEDs) have shown great potential for plant growth and development, with higher luminous efficiency and more flexible and feasible spectral control compared with other artificial lighting. The combined effects of red and blue (RB) LED with or without green (G) LED light and white LED light on lettuce (Lactuca sativa L.) growth and physiology, including nitrate content, chlorophyll fluorescence, and phytochemical concentration before harvest, were investigated. Continuous light exposure at preharvest can effectively reduce nitrate accumulation and increase phytochemical concentrations in lettuce plants. Nitrate accumulation is dependent on the spectral composition and duration of treatment: lettuce exposed to continuous RB (with or without G) LED light with a photosynthetic photon flux (PPF) of 200 µmol·m−2·s−1 exhibited a remarkable decrease in nitrate content at 24 hour compared with white LED light treatment at the same PPF. In addition, RB LED light (R:B = 4:1) was more effective than white LED light at the same PPF in facilitating lettuce growth. Moreover, continuous LED light for 24 hours significantly enhanced free-radical scavenging activity and increased phenolic compound concentrations. We suggest that 24 hours continuous RB LED with G light exposure can be used to decrease nitrate content and enhance lettuce quality.

Postharvest light treatments increase skin blush in mango fruit

Skin colour is an important quality parameter that influences mango fruit marketability. The mango industry is interested in controlled induction of skin blush in mangoes. It is desirable to understand the control of anthocyanin accumulation in mango skin. Among environmental factors known to induce anthocyanin accumulation in plants, light is the most studied. Light exposure induces pigmentation in various fruits, including apple, strawberry and grape. The effect of different light qualities on skin blush in mango fruit has received relatively little attention. The objective of this study was to assess anthocyanin accumulation and blush in response to blue, red and far red light from light-emitting diodes (LEDs) as applied to harvested mango fruit skin during storage at 12°C. Except for red light, the other wavelengths induced anthocyanin accumulation and skin blush as compared to the dark control treatment. Anthocyanin concentration and a∗ values were highest in blue light exposed fruit skin. This wavelength enhanced phenylalanine ammonia lyase activity in the mango skin, which may be associated with increased pigmentation. LED light treatment did not affect other fruit quality parameters at 21 days of storage, including firmness, total soluble solids and titratable acidity. Overall, the findings suggest that postharvest treatment with blue light can induce skin blush in mango fruit, which potentially may enhance their commercial value.

Effect of the combination of ethylene and red LED light irradiation on carotenoid accumulation and carotenogenic gene expression in the flavedo of citrus fruit

The effects of ethylene and red light-emitting diode (LED) light (660nm) on the accumulation of carotenoid and expression of genes related to carotenoid biosynthesis were investigated in the flavedo of Satsuma mandarin. The results showed that the contents of β-cryptoxanthin, all-trans-violaxanthin, 9-cis-violaxanthin and lutein were simultaneously increased along with the total carotenoid accumulation by the red LED light. With the ethylene treatment, the contents of β-carotene and β-cryptoxanthin were increased, while the content of lutein was decreased in the flavedo. The suppression of lutein accumulation by ethylene was inhibited when the ethylene treatment was performed under the red LED light. With the combination of ethylene and red LED light treatments, the contents of β-cryptoxanthin and lutein were simultaneously increased. Gene expression results showed that simultaneous increases in the expression of CitPSY, CitPDS, CitZDS, CitCRTISO, CitLCYb1, CitLCYb2, CitLCYe, CitHYb, and CitZEP contributed to the accumulation of β-cryptoxanthin and lutein in the treatment of ethylene combined with red LED light. The results presented might provide new strategies to enhance the commercial and nutritional value of citrus fruit.