Light-emitting Diodes Light Treatments Research Articles

Violet LED light-activated MdHY5 positively regulates phenolic accumulation to inhibit fresh-cut apple fruit browning.

Fresh-cut fruit browning severely affects the appearance of fruit. Light treatment can effectively inhibit fresh-cut apple fruit browning, but the regulatory mechanism remains unknown. Here, we discovered that violet LED (Light-Emitting-Diode) light treatment significantly reduced fresh-cut apple fruit browning. Metabolomic analysis revealed that violet LED light treatment enhanced the phenolic accumulation of fresh-cut apple fruit. Transcriptomic analysis showed that the expression of phenolic degradation genes POLYPHENOL OXIDASE (MdPPO) and PEROXIDASE (MdPOD) was reduced, and the expression of phenolic synthesis gene PHENYLALANINE AMMONIA LYASE (MdPAL) was activated by violet LED light treatment. Moreover, two ELONGATED HYPOCOTYL 5 (MdHY5 and MdHYH) transcription factors involved in light signaling were identified. The expression of MdHY5 and MdHYH was activated by violet LED light treatment. Violet LED light treatment no longer inhibited fresh-cut apple fruit browning in MdHY5- or MdHYH- silenced fruit. Further experiments revealed that MdHY5 and MdHYH suppressed MdPPO and MdPOD expression and promoted MdPAL expression by binding to their promoters. In addition, MdHY5 and MdHYH bound to each other's promoters and enhanced their expression. Overall, our findings revealed that violet LED light-activated MdHY5 and MdHYH formed a positive transcriptional loop to regulate the transcription of MdPPO, MdPOD, and MdPAL, which in turn inhibited the degradation of phenolics and promoted the synthesis of phenolics, thus inhibiting fresh-cut apple fruit browning. These results provide a theoretical basis for improving the appearance and quality of fresh-cut apple fruit.

Improving Inoculum Production of Arbuscular Mycorrhizal Fungi in Zea mays L. Using Light-Emitting Diode (LED) Technology

A substrate-based production system is a simple and low-cost method for arbuscular mycorrhizal (AM) fungal inoculum production. However, it is time-consuming and typically yields low numbers of AM fungal spores due to several factors affecting plant growth efficiency. Our study investigated the use of light-emitting diode (LED) technology to expedite AM fungal spore production in planta. We performed experiments with Rhizophagus irregularis inoculated in maize (Zea mays L.), contrasting LED light with greenhouse (GH) conditions. Our results exhibited a significant improvement in AM fungal colonization and spore production, as well as a reduction in the production period from 120 to 90 days under the LED light condition. This was achieved using a red-and-blue light ratio of 60:40 with a total light intensity of 300 µmol m−2 s−1. The LED light treatments improved maize growth by increasing nitrogen (N) and phosphorus (P) concentrations in shoots and roots, respectively. Our gene expression analyses revealed that in AMF-inoculated plants, genes related to photosynthesis were significantly upregulated under LED light compared to the GH condition. Moreover, LED increased the expression of marker genes linked to the AM fungi-related cell cycle, indicating enhanced AM fungal growth during symbiosis. These findings advance our comprehension of LED applications in agriculture, offering promising prospects for acceleration of AM fungal spore production.

LED light treatments enhance neuroprotective properties and differentially impact phenolic compounds and triterpenoid content in Gotu Kola (Centella asiatica (L.) Urb.)

Due to an array of medicinal properties being attributed to Gotu kola (Centella asiatica (L.) Urb.), there is a growing demand for the incorporation of the plant as an herbal ingredient in drugs, cosmetics but mainly in dietary supplements and herbal drugs, which has been causing a gradual decline on its wild population. A possible way might be the improvement of the content in bioactive constituents that, in this specific matter, have been mainly labelled as being pentacyclic triterpenoids. We hypothesize that using light-emitting diode (LED) treatments can enhance its content in bioactives and improve its neuroprotective effects.Specific LED light treatments caused a metabolic shift, globally reducing the concentrations of the triterpenoids madecassoside, asiaticoside, and their corresponding aglycones. However, LED light treatments caused a pronounced increase in specific phenolic bioactives in comparison with samples obtained under sunlight, mostly pronounced in the concentrations of di-O-caffeoylquinic acids. Principal component analysis corroborated that the improvement on the neuroinflammatory status in BV-2 microglial cells and enhanced inhibition of tyrosinase are correlated with the increase in specific phenolic constituents resulting from LED light treatments.While the anti-neuroinflammatory effects in BV-2 microglial cells are demonstrated here for the first time, our core findings are mostly crucial for meeting the increased demand for C. asiatica in herbal products, as our LED light treatment boosts yields in specific phenolic bioactives and improves neuroprotective effects.

Integrated Dose-Effect Relationship of Near-Infrared Light-Emitting Diode Light on Bone Regeneration in Disuse Osteoporosis Rats.

Objective: To examine the integrated dose-effect relationship of near-infrared (NIR) light-emitting diode (LED) light therapy in promoting bone defect repair in the rat model for osteoporosis (OP). Background: Low-intensity laser therapy has been shown to promote bone regeneration in OP rats. However, its integrated dose-effect relationship is not clear. Methods: Twenty-week-old male Sprague-Dawley rats were randomly assigned to 11 groups: (1) no-treatment control group (C group), (2) tail suspension (TS)-induced disuse OP experimental group (TS-OP group), and (3) OP rats with LED light treatment at nine dosages (L1-L9 groups). The tail of the rat was tied and suspended on the beam of the cage to suspend their hind limbs to induce bone loss for 4 or 7 weeks. The rats were then released and returned to their regular positions. An NIR LED at 810 nm was used on the bilateral hind limbs daily for 4 weeks. The C group rats were not given any treatment. The TS-OP group rats were subjected to identical procedures with L groups, with the exception that the light power was not turned on. After the experiment, the dual-energy X-rays or the microcomputed tomography scan analysis was performed to evaluate bone tissue status. Data analysis was done using SPSS and the health scale. Results: The trabecular thickness, trabecular number, bone volume/total volume, and connectivity density of cancellous bone and the biomechanical properties of femur in light groups were significantly increased compared with the TS-OP group, while the trabecular separation and structure model index were significantly decreased. Conclusions: NIR LED light therapy may promote trabecular bone repair of TS-OP rats. Light intensity influences photobiomodulation. In our dose levels, the greater the light intensity, usually the more effective.

Manipulation of light spectrum is an effective tool to regulate biochemical traits and gene expression in lettuce under different replacement methods of nutrient solution

The use of light-emitting diode (LED) technology represents a promising approach to improve plant growth and metabolic activities. The aim of this study was to investigate the effect of different light spectra: red (656 nm), blue (450 nm), red/blue (3:1), and white (peak at 449 nm) on biochemical properties, photosynthesis and gene expression in two lettuce cultivars (Lollo Rossa and Lollo Bionda) grown under different methods of nutrient solution replacement in hydroponics. Complete replacement and EC-based replacement of nutrient solution increased content of proline and soluble sugars and activity of antioxidant enzymes (CAT, GPX and SOD) under the red/blue LED and red LED light treatments in both cultivars. In addition, the red/blue and the monochromatic red light increased the soluble protein content and the antioxidant activity in the Lollo Rosa cultivar under the replacement method according to the needs of the plant. An increase in flavonoid content in the EC-based method in the Lollo Rosa variety treated with a combination of red and blue light was also observed. The red/blue light had the greatest induction effect on anthocyanin content, expression of the UFGT, CHS, and Rubisco small subunit genes, and the net photosynthetic rate. Data presented here will directly contribute to the development of nutrient solution and LED spectrum management strategies to significantly improve plant growth and metabolism, while avoiding water and nutrient waste, and environmental pollution.

The influence of LEDs with different blue peak emission wavelengths on the biomass, morphology, and nutrient content of kale cultivars

Light-emitting diodes (LEDs) enhance plant production in vertical farms by regulating photosynthetic rate and phytochemistry. Specific light recipes can be formulated using LEDs for high output by fine-tuning spectral composition and irradiance. In this study, the growth, development, and nutritional quality of three kale cultivars (‘Toscano’, ‘Redbor’, and ‘Winterbor’) were examined under different blue peak emission wavelengths (λpeak). Photosynthetic photon flux density (PPFD) was maintained at 200 ± 10% μmol m − 2s − 1 over a 16-hr photoperiod. The LED light treatments had blue λpeak centered at 400, 420, and 450 nm wavelengths, all with spectral ratios of 20% blue, 20% green, 60% red in the visible light region, and 15% of total PPFD in the far-red region. The control light was cool-white fluorescent (CWF) light with blue λpeak at 436 nm and a slightly higher amount of PPFD in the blue region (23%). The biomass yield and leaf physical characteristics were largely unaffected by the light treatments with different blue λpeak. However, the concentration of carotenoids and chlorophylls in kale leaves was influenced by the type and amount of blue light during growth. Future research should investigate the effect of different blue light percentages in pre- and post-harvest LED treatments (continuous or pulsed) on high-value, nutritious crops.

Blue LED light treatment inhibits virulence and patulin biosynthesis in Penicillium expansum

Blue light-emitting diode (LED) light has been considered to influence the growth, quality, and preservation of certain fruit and vegetable. However, the blue LED light impact on apple postharvest blue mold remains elusive. In this study, the influence of blue LED light on Penicillium expansum virulence and patulin secretion was investigated in vitro and in vivo, as well as on the apple quality. The growth of P. expansum was inhibited by blue LED light via changes in mycelium morphology changes, cell membrane integrity, and potential mitochondrial membrane destruction, thereby causing reactive oxygen species accumulation, oxidative stress, and mitochondrial dysfunction. Furthermore, the expression level of LaeA relevant to the pathogenicity of P. expansum, was down-regulated. Specifically, the patulin production of P. expansum was inhibited via expression down-regulation of the patulin biosynthesis-related genes PatA, PatE, and PatN rather than direct degradation by the blue LED light treatment. Additionally, no significant effects on the fruit quality were observed when the light intensity was lower than 120 μmol m-2 s-1. In summary, blue LED light treatment has the potential for a low-cost, safe, and non-chemical approach to control apple postharvest decay.

Specific wavelength LED light pulses modify vitamin C and organic acids content in raspberry and blackberry fruit during postharvest

ABSTRACT Light-emitting diodes (LED) have emerged as a non-polluting and energy-saving technology in fruit postharvest. The aim of this work was to evaluate the effect of different LED light pulses during raspberries´ and blackberries´ postharvest under cold storage. Fruit was exposed to short LED light pulses (Green, Blue, Red, and Red+Blue) of 15 min every 2 h for 7 and 14 d of storage at 4°C. Raspberries were more susceptible to water loss. Short LED light pulses decreased internal breakdown in raspberries, and minor effects of LED treatments were observed in blackberries. After 7 d of cold storage, in raspberries, Green, Blue, and Red light treatments increased the content of quinic and malic acids, and only Green and Blue LED sources also increased ascorbic acid content. In addition, Blue, Green, and Blue+Red LED light treatments exhibited a higher level of citric acid at 14 d. In blackberries, fruit changes were mainly because of the cold storage. Overall, these results showed that short LED light pulses can extend the postharvest life of raspberries, decreasing internal breakdown and increasing the content of ascorbic acid, suggesting that different Rubus species have distinct physiological processes underlying ripening and light interactions.

Effects of Artificial Light Spectra and Sucrose on the Leaf Pigments, Growth, and Rooting of Blackberry (Rubus fruticosus) Microshoots

Light emitting diodes (LEDs) are potential light sources for in vitro plant cultures. Here, axillary blackberry shoots were grown in MS medium with indole-3-butyric acid (1 mg L−1), naphthalene acetic acid (0.5 mg L−1), and sucrose supplementation (0–60 g L−1) and the cultures were incubated under four light treatments: three LED light treatments (blue + red light (2:1 spectral ratio), blue + red light (1:2), and cool + warm white light (1:1)) and a standard florescent tube white spectrum treatment. Sucrose was indispensable for rooting of blackberry microshoots. Sucrose concentrations up to 45 g L−1 increased total root length and root surface area under all light treatments. However, at this sucrose concentration, leaf area and vegetative growth were negatively affected. Plantlets grown in media containing 15–30 g L−1 of sucrose exhibited the highest leaf pigments, shoot length, and number of leaves. LED treatments increased leaf pigments as compared with florescent treatment. Plantlets grown under blue + red light (2:1) had the highest stoma aperture length and width, whereas cool + warm white light resulted in the lowest values. Among the LED treatments, blue + red light (2:1) resulted in the highest leaf area, chlorophyll and carotenoid contents, and vegetative growth, whereas fluorescent resulted in the lowest values. A combination of blue and red light at a 2:1 spectral ratio with 30 g L−1 of sucrose is recommended for the optimal in vitro rooting and vegetative growth of blackberry microshoots.

Performance of Different Lettuce Cultivars Grown Hydroponically under Fluorescent and Light-emitting Diode Light Growth Conditions

Lettuce (Lactuca sativa L.) is one of the most consumed fresh vegetables in the United States. However, lettuce production is heavily limited to California and Arizona, posing a high risk to the supply chain. Hydroponic production is a soilless cultivation method and provides a sustainable alternative to growing lettuce in the field. Light is a critical factor in plant development, and light quality highly affects plant morphogenesis. The goals of this study were 2-fold, with the first to investigate the growth of 26 lettuce cultivars under a hydroponic system supplemented with fluorescent light to determine adaptability. Subsequently, the second goal was to determine how light-emitting diodes (LEDs) affect lettuce plant morphology and photosynthesis compared with fluorescent light for four lettuce cultivars. Results showed that 23 of 26 lettuce cultivars were grown successfully using a hydroponic system. However, lettuce grown under fluorescent light experienced stem elongation—a morphological response to low-light conditions known as shade avoidance syndrome. Stem elongation decreased significantly under LED light, whereas other morphological characteristics remained relatively the same between the two light treatments. Although there were no differences in dry weight and leaf area, the carbon assimilation rate increased significantly in lettuce cultivars Coastal Star, Muir, Green Butter, and Rouge d’Hiver when treated with LED light. Correspondingly, intercellular carbon dioxide (CO2) decreased in these four lettuce cultivars under the LED light treatment. Our study results indicate that LED light increased photosynthetic activity and reduced stem elongation to enhanced lettuce quality.

Effect of LED Light Color on Color Brightness, Growth, and Survival of Comet Fish (Carassius auratus)

Comet fish (Carassius auratus) is a type of freshwater ornamental fish with a high selling value due to its unique body shape and bright colour. The purpose of this study was to evaluate the effect of different LED (Light Emitting Diode) light colours on colour brightness, growth, and survival of comet fish. This study applies an experimental approach with an experimental design in the form of a completely randomized design (CRD) and consists of 5 light treatments and 3 replications, namely A (room light), B (white LED), C (blue LED), D (green LED), and E (red LED). The results showed that LED light treatment had a significant effect on the colour quality and feed efficiency, but did not significantly affect the growth and survival of comet fish. The best colour quality was found in treatment E (red LED) with an increase in the TCF (Toca Color Finder) score of 6.22 and colour performance on the back by 80.80%, pectoral fin colour by 64.91%, and tail fin by 71 .18%. The best feed efficiency was obtained in treatment C (blue LED) with a feed efficiency value of 57.48%. The behavioural responses of comet fish did not make any difference between each LED treatment. The water quality of the comet fish rearing media has a temperature value ranging from 25.70 – 29.20 C. The pH value ranges from 7.29 to 8.50. Meanwhile, dissolved oxygen ranges from 8.00 – 12.20 mg/L

Effect of Light-emitting Diodes, Ultraviolet-B, and Fluorescent Supplemental Greenhouse Lights on Strawberry Plant Growth and Response to Infection by the Anthracnose Pathogen Colletotrichum gloeosporioides

Supplemental lighting is frequently used to extend daylength for strawberries (Fragaria ×ananassa) grown in greenhouses and high tunnels; however, information is limited on the effect of these lights on disease development. We evaluated the effect of ambient light and six supplemental light treatments [red, blue, and white light-emitting diodes (LEDs), separately; a combination of red, blue, and white LEDs; wide-spectrum fluorescent (WSF); and WFS + ultraviolet B (UV-B)] on plant growth and disease response of strawberries grown in a greenhouse. Plants were exposed to supplemental light treatments for 17 h each day. In the WSF+UV-B treatment, plants were exposed to WSF light during the day and to UV-B light for 3 hours during the night. Two trials were conducted; each trial contained five or six cultivars and was replicated three times. Twice during each trial, detached leaves from each cultivar in each light treatment were inoculated with a conidial suspension of the anthracnose crown rot pathogen, Colletotrichum gloeosporioides and rated for disease severity 10 days later. There was a significant difference due to light treatment and to cultivar in relative chlorophyll content and plant growth parameters. Plant injury ratings were lowest in the white LED, WSF, and WSF+UV-B treatments. Plants in the combination LED and red LED light treatments received higher injury, lower vigor scores, and lower relative chlorophyll content values than plants in all other light treatments. After inoculation of detached strawberry leaves with C. gloeosporioides in Trial 1, there was a significant effect due to light treatments on disease severity ratings (DSRs) after 18 weeks’ exposure to light treatments with the DSRs in the WSF+UV-B treatment being lower than those in all other treatments except those in the red LED treatment. There was not a significant effect in DSRs due to light treatments after 24 weeks in Trial 1 or after 4 or 22 weeks in Trial 2. There were significant effects due to cultivar on DSRs in both trials: ‘Strawberry Festival’, ‘Pelican’, and ‘Seascape’ received the lowest DSRs. This study showed an effect of supplemental light on several strawberry plant growth parameters, including a harmful effect of high-intensity red LED irradiation.

The LED wavelength, lighting intensity, feather coverage, and novelty inclusion in turkey hens

Light-emitting diodes (LED) have been gaining acceptance in agriculture applications as alternatives to incandescent light sources. Daylength intensity and spectral wavelength are important in poultry production and also, in some cases, serve as the only mean of light in some facilities. Therefore, Large White turkey hens of the same strain were reared to market weights using two different housing facilities in combination with different LED light treatments. Each treatment within the environmentally controlled facility (ECF) consisted of four replicate rooms, 16 rooms total in the facility. LED bulbs consisted of 5,000 Kelvin (K) or 2,700K LED in conjunction with a high or low foot-candle (FC) intensity level. Daylength was fixed at 14L:10D. Additionally, birds were reared in a natural curtain-sided facility (6 replicate pens) with exposure to natural light with a 75W incandescent bulb to maintain daylength consistency with the ECF. Performance parameters were measured at 0, 5th, 9th, and 12th week (wk) of age. Serum triiodothyronine (T3) and right eye measurements were taken at the 5th and 9th wk of age. Feather coverage was assessed at the 9th and 12th wk old as indicators of bird wellbeing. Novelty interactions for visual or nutritional items were recorded at 7th wk old. Spectral output within the same Kelvin temperature was significantly altered during dimming to achieve intensity levels. There were mixed performance results; however, cumulatively, birds reared under LED lighting, regardless of LED type or intensity level, had consistently increased body weight. Bird wellbeing was altered under 5,000K LED in combination with 2 FC as measured by a significant elongation of the anterior-posterior distance. However, the same effect was not measured in the 5,000K, 10 FC treatment, or in the 2,700K treatments, regardless of FC measurement. There were no differences among treatments for T3, feather coverage, or latency to approach or interact with novel items. When LED lights are used in environmentally controlled facilities, coupled with novelty interactions, birds maintained and excelled in performance parameters when compared to birds reared with natural light and ventilation conditions.

The influences of light-emitting diodes (LEDs) on the phenolic content and antioxidant enzymes of basil using a plant factory system

We used two types of Ocimum basilicum plants and white light-emitting diode (LED) lights as controls (plant factory unit 1, PFU 1). We applied four composite LED light treatments, 125:125:125 white, red, blue (PFU 2), 0.0:250:125 white, red, blue (PFU 3), 125:125:57 white, red, blue (PFU 4) and 125:57:125 white, red, blue (PFU 5) to evaluate light quality effects on antioxidant capacity of O. basilicum plants. The results revealed that the composite lights of PFUs 2,3,4 and 5 were beneficial for the accumulation of flavonoids and glutathione but were not beneficial forthe proanthocyanidin content; the plants subjected to the PFUs 2,3,4 and 5 treatments had a higher laccase activity and proline content and a lower malondialdehyde (MDA) content, polyphenol oxidase activity and peroxidase activity than the control plants.Analysis via high-performance liquid chromatography revealed that protocatechuic acid, gentisic acid, chlorogenic acid, syringic acid, cinnamic acid, quercetin, apigenin, kaempferol, chrysin, p-hydroxybenzoic acid, p-coumaric acid, apigenin-7-glucoside, rutin, rosmarinic acid were the major phenolic components in the O. Basilicum extracts, and sufficient composite lighting of O. basilicum plants significantly enhanced these antioxidant concentrations. Our results indicate that the use of LEDs with different light qualities to irradiate O. basilicum significantly improved the antioxidant capacity which could be a beneficial for nutrition and health benefits.

Effect of Light Emitting Diode (LED) Spectrum at Seedlings Production for Optimal Growth on Different Type of Lettuce in MARDI Plant Factory

Seedling production is a crucial part of the production of fresh vegetables in a plant factory. Light is one of the necessities for plants to produce a healthy seedling before being transplanted to the production area. Different light formulations resulted in different growth performances of the plant. Hence, this study was conducted to aim for suitable light formulation on various types of lettuce in the MARDI Plant Factory. The study was conducted in two stages: 1) seedling production and 2) production area. Treatments were evaluated at the seedlings' production stage using the split-plot experimental design with four replications. LED light treatments (LT) was the main factor with the various ratio of spectrum colour of Red (R), Blue (B), Green (G) and full spectrum. (LT 1; 5R:1B, LT 2; 1R:1B, LT 3; 1R: 2B, LT 4; 2R:1B, LT 5; 4R:1B:1G and LT 6; Full spectrum as control). The sub-factor was lettuce variety (V1; Butterhead, V2; Green Coral, V3; Red Coral and V4; Mini Cos). Variables measured at seedlings production were seed germination. Growth biomass and SPAD value were evaluated in the production area. At seedlings production, the full spectrum lighting shows significant seeds germination percentage compared to other LED lighting, and V1 performed well on germination percentage and time compare to other varieties. The interaction between light treatments and lettuce was observed on the leaf numbers, shoot fresh weight, leaf area, and the shoot-root ratio at the production area. LT 1 and LT 5 on butterhead and green coral significantly affected the number of leaves and leaf area, which were relatively influenced by light quality and ambient temperature. The yield on green coral lettuce grown under LT 1, LT 2, and LT 5 was significantly higher than others. However, plant biomass and SPAD value for all treatments were not significantly different. The allometry of plant was expressed on a shoot-root ratio with LT 2 on green coral shows a significantly higher shoot-root ratio than other treatments. The study's findings showed that light treatment with Red and Blue LED ratio of 5:1, 1:1, and Red, Blue, and Green LED ratio of 4:1:1 light arrangement on the seedling's productions provided optimal growing conditions in the production area butterhead and green coral lettuce in MPF cultivation.

Effect of Light-Emitting Diodes (LEDs) on Some Physical and Bioactive Compounds of ‘Iceberg’ Lettuce (Lactuca Sativa L.)

Abstract The use of light-emitting diodes (LEDs) is a recent concerned application in the indoor crop system of the modern plant production. In our research, we evaluated the influence of four monochromic LED lights including 100% White (W), Yellow (Y), Red (R) and Blue (B) in comparison to solar lightening condition (GR) as a control. In this regard, some morphological characteristics and biochemical content of the common outdoor ‘Iceberg’ lettuce (Lactuca sativa L.) was measured. The results show that leaf length, leaf area and total head weight were significantly greater in the plants grown under B LED, while all the other physical parameters were significantly higher in the plants grown under GR environmental conditions. On the other hand, chlorophyll (Chl), carotenoids (Car), and nitrate content were also influenced by different light treatments. Plants grown under LED light treatment resulted in significantly higher chlorophyll content compared to the control. However, significantly greater carotenoid content was in the plants grown under GR condition. The highest total chlorophyll content was recorded under B and R LED, whereas the lowest was in the GR condition. The lowest nitrate content in the blade and petiole was recorded in the plants grown under Y LED, while the highest nitrate content was recorded in the GR. Based on our result, it is possible to grow and improve some quality parameters of common outdoor ‘iceberg’ lettuce under LED where the solar light is limited or unavailable. Thus, plants performed better under GR light conditions than monochromic LEDs; however, some LED lights could improve some quality parameters and biochemical contents in the ‘iceberg’ lettuce variety.

The Effect of Supplementary LED Lighting on the Morphological and Physiological Traits of Miniature Rosa × Hybrida 'Aga' and the Development of Powdery Mildew (Podosphaera pannosa) under Greenhouse Conditions.

We investigated the growth traits, flower bud formation, photosynthetic performance, and powdery mildew development in miniature Rosa × hybrida ‘Aga’ plants grown in the greenhouse under different light-emitting diode (LED) light spectra. Fluorescence-based sensors that detect the maximum photochemical efficiency of photosystem II (PS II) as well as chlorophyll and flavonol indices were used in this study. Five different LED light treatments as a supplement to natural sunlight with red (R), blue (B), white (W), RBW+FR (far-red) (high R:FR), and RBW+FR (low R:FR) were used. Control plants were illuminated only by natural sunlight. Plants were grown under different spectra of LED lighting and the same photosynthetic photon flux density (PPFD) (200 µmol m−2 s−1) at a photoperiod of 18 h. Plants grown under both RBW+FR lights were the highest, and had the greatest total shoot length, irrespective of R:FR. These plants also showed the highest maximum quantum yield of PS II (average 0.805) among the light treatments. Red monochromatic light and RBW+FR at high R:FR stimulated flower bud formation. Moreover, plants grown under red LEDs were more resistant to Podosphaera pannosa than those grown under other light treatments. The increased flavonol index in plants exposed to monochromatic blue light, compared to the W and control plants, did not inhibit powdery mildew development.

Effects of Light-Emitting Diodes on the Accumulation of Phenolic Compounds and Glucosinolates in Brassica juncea Sprouts

Recent improvements in light-emitting diode (LED) technology afford an excellent opportunity to investigate the relationship between different light sources and plant metabolites. Accordingly, the goal of the present study was to determine the effect of different LED (white, blue, and red) treatments on the contents of glucosinolates (glucoiberin, gluconapin, sinigrin, gluconasturtiin, 4-methoxyglucobrassicin, 4-hydroxyglucobrassicin, glucobrassicin, and neoglucobrassicin) and phenolic compounds (4-hydroxybenzonate, catechin, chlorogenic acid, caffeate, gallate, sinapate, and quercetin) in Brassica juncea sprouts. The sprouts were grown in a growth chamber at 25 °C under irradiation with white, blue, or red LED with a flux rate of 90 μmol·m−2·s−1 and a long-day photoperiod (16 h light/8 h dark cycle). Marked differences in desulfoglucosinolate contents were observed in response to treatment with different LEDs and different treatment durations. In addition, the highest total desulfoglucosinolate content was observed in response to white LED light treatment, followed by treatment with red LED light, and then blue LED light. Among the individual desulfoglucosinolates identified in the sprouts, sinigrin exhibited the highest content, which was observed after three weeks of white LED light treatment. The highest total phenolic contents were recorded after one week of white and blue LED light treatment, whereas blue LED irradiation increased the production of most of the phenolic compounds identified, including 4-hydroxybenzonate, gallate, sinapate, caffeate, quercetin, and chlorogenic acid. The production of phenolics decreased gradually with increasing duration of LED light treatment, whereas anthocyanin accumulation showed a progressive increase during the treatment. These findings indicate that white LED light is appropriate for glucosinolate accumulation, whereas blue LED light is effective in increasing the production of phenolic compounds in B. juncea sprouts.

Red LED light treatment promotes cognitive learning through up-regulation of trpm4 in zebrafish

Although light emitting diodes (LEDs) are widely used in our daily lives, there is little research regarding LED light’s possible effects on biological functions. We used a zebrafish animal model to investigate the long-term effects of white, blue and red LED lights on cognitive learning and memory recall. Our data suggest that these treatments had not only an impact on learning but also surprisingly long-lasting effects, particularly with regard to individuals treated with red light. The qPCR results revealed that the expression levels of trpm4, trpa1b, grin2aa and dlg4 in the skin were increased after monochromatic light treatment. Furthermore, the up-regulation of trpm4 in the brain may correlate to enhanced learning and memory following red-light treatment. Our results identify a light-based stimulation system for enhancing zebrafish learning, which has the potential to provide important insights into the relationship between LED lighting and animal behaviour.

LED lighting affected the growth and metabolism of eggplant and tomato transplants in a greenhouse

Light-emitting diodes (LEDs) were used for the spring greenhouse cultivation of eggplant (Solanum melongena L.) ‘Milar F1’ and tomato (S. lycopersicon L.) ‘Benito F1’ transplants. Seedlings were grown under natural light conditions with the supplemental LED light. A 16-h photoperiod provided plants with a DLI of 12.6 (eggplant) and 9.6 (tomato) mol m2/day. Four supplemental light spectra were tested: L1 (90% red + 10% blue); L2 (80% red + 20% blue); L3 (43% red + 42% blue+15% green) and L4 (56% red + 26% blue + 15% green + 3% UV-A). The PPFD in each LED light treatment was 150 ± 20 µmol/m2·s. Compared to the control plants (without LED lighting), the eggplant transplants had about a 25% larger leaf area and a higher level of total phenol content as well as a higher antiradical scavenging activity under the L1 spectrum. The favourable spectrum for the tomato transplants consisted of red to blue in a ratio of 1 : 1 mixed with a green light (L3) – the leaves were characterised by a higher content of dry matter, soluble sugars, photosynthetic pigments and total phenols; also the radical scavenging activity increased in comparison to the control group. It was shown that the supplemental irradiation of transplants was economically acceptable.