Responses of strawberry plantlets cultured in vitro under superbright red and blue light-emitting diodes (LEDs)

Unrooted strawberry cv. `Akihime' shoots with three leaves obtained from standard mixotrophic cultures were cultured in the ``Culture Pack'-rockwool system with sugar-free MS medium under CO<sub>2</sub>-enriched condition. To examine the effect of superbright red and blue light-emitting diodes (LEDs) on in vitro growth of plantlets, these cultures were placed in an incubator, ``LED PACK', with either red LEDs, red LEDs1blue LEDs or blue LEDs light source. To clarify the optimum blue and red LED ratio, cultures were placed in ``LED PACK 3' under LED light source with either 100, 90, 80, or 70% red + 0, 10, 20, 30% blue, respectively, and also under standard heterotrophic conditions. To determine the effects of irradiation level, cultures were grown under 90% red LEDs + 10% blue LEDs at 45, 60 or 75 mol m^–2 s^–1 . Plantlet growth was best at 70% red + 30% blue LEDs. The optimal light intensity was 60 mol m^–2 s^–1. Growth after transfer to soil was also best after in vitro culture with plantlets produced were 70% red LEDs + 30% blue LEDs.     

LED irradiance level affects growth and nutritional quality of Brassica microgreens

This study examines the effect of irradiance level produced by solid-state light-emitting diodes (LEDs) on the growth, nutritional quality and antioxidant properties of Brassicaceae family microgreens. Kohlrabi (Brassica oleracea var. gongylodes, ‘Delicacy Purple’) mustard (Brassica juncea L., ‘Red Lion’), red pak choi (Brassica rapa var. chinensis, ‘Rubi F₁’) and tatsoi (Brassica rapa var. rosularis) were grown using peat substrate in controlled-environment chambers until harvest time (10 days, 21/17°C, 16 h). A system of five lighting modules with 455, 638, 665 and 731 nm LEDs at a total photosynthetic photon flux densities (PPFD) of 545, 440, 330, 220 and 110 µmol m^?2s^?1 respectively were used. Insufficient levels of photosynthetically active photon flux (110 µmol m^?2 s^?1) suppressed normal growth and diminished the nutritional value of the Brassica microgreens studied. In general, the most suitable conditions for growth and nutritional quality of the microgreens was 330–440 µmol m^?2 s^?1 irradiation, which resulted in a larger leaf surface area, lower content of nitrates and higher total anthocyanins, total phenols and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging capacity. High light levels (545 µmol m^?2 s^?1), which was expected to induce mild photostress, had no significant positive impact for most of investigated parameters.     

Growth and cell cycle of Ulva compressa (Ulvophyceae) under LED illumination

The cell‐cycle progression of Ulva compressa is diurnally gated at the G₁ phase in accordance with light–dark cycles. The present study was designed to examine the spectral sensitivity of the G₁ gating system. When blue, red, and green light‐emitting diodes (LEDs) were used for illumination either alone or in combination, the cells divided under all illumination conditions, suggesting that all colors of light were able to open the G₁ gate. Although blue light was most effective to open the G₁ gate, red light alone or green light alone was also able to open the G₁ gate even at irradiance levels lower than the light compensation point of each color. Occurrence of a period of no cell division in the course of a day suggested that the G₁ gating system normally functioned as under ordinary illumination by cool‐white fluorescent lamps. The rise of the proportion of blue light to green light resulted in increased growth rate. On the other hand, the growth rates did not vary regardless of the proportion of blue light to red light. These results indicate that the difference in growth rate due to light color resulted from the difference in photosynthetic efficiency of the colors of light. However, the growth rates significantly decreased under conditions without blue light. This result suggests that blue light mediates cell elongation and because the spectral sensitivity of the cell elongation regulating system was different from that of the G₁ gating system, distinct photoreceptors are likely to mediate the two systems.     

Effects of different spectral lights on <Emphasis Type="Italic">Oncidium</Emphasis> PLBs induction,proliferation, and plant regeneration

The effects of different spectral light distribution on in vitro induction and proliferation of Oncidium protocorm-like bodies (PLBs) and subsequent growth of plantlets were investigated. Shoot tips (5 mm in length) of proliferating shoots of Oncidium “Gower Ramsey” were vertically incubated on 1/2 Murashige and Skoog (MS) medium supplemented with 1.0 mg l⁻¹ 6-benzyladenine (BA), and grown under either monochromatic red light-emitting diodes (LEDs) (RR), blue LEDs (BB), yellow LEDs (YY) or green LEDs (GG). Cultures grown under fluorescent lamps (FL) were used as control. Selected FL-induced PLBs were cut into 3- to 4-mm sections and incubated on MS medium supplemented with 1.0 mg l⁻¹ BA and 0.5 mg l⁻¹ α-naphthaleneacetic acid (NAA), and grown under RR, BB, YY, GG, or FL. Moreover, FL-differented shoots (15 mm in length with two leaves) were incubated on 1/2 MS medium with 0.5 mg l⁻¹ NAA, and grown under either FL, RR, 10% blue + 90% red LEDs (1BR), 20% blue + 80% red LEDs (2BR), 30% blue + 70% red LEDs (3BR), BB, 80% red + 10% blue + 10% far-red LEDs (RBFr), or 80% red + 10% blue + 10% green LEDs (RBG). Overall, the red light spectrum enhanced induction, proliferation, and the carbohydrate contents of PLBs, as well as subsequent plantlet lengths, while the blue spectrum promoted differentiation, protein accumulation, and enzyme activities in PLBs, as well as pigment content accumulation in PLBs and developing plantlets. The combination of red and blue LEDs resulted in higher energy efficiency as well as dry weight and enzyme activities in these plantlets.     

Impact of light-emitting diode irradiation on photosynthesis,phytochemical composition and mineral element content of lettuce cv. Grizzly

Light-emitting diodes (LEDs) are a promising technology with a potential to improve the irradiance efficiency, light quality, and the light spectrum for increasing plant yield and quality. In this experiment, we investigated the impacts of various LED light qualities, including 100% red, 100% blue, 70% red + 30% blue, and 100% white, on the growth and photosynthesis, phytochemical contents, and mineral element concentrations in lettuce (Lactuca sativa L. cv. ‘Grizzly’) in comparison to normal greenhouse conditions. Photon flux of 300 µmol m^?2 s^?1 was provided for 14 h by 120 LEDs set on a 60 cm × 60 cm sheet of aluminum platform in the growth chambers, where plants were grown for 60 d. Fresh mass per plant was significantly higher when grown under 100% blue and 70% red + 30% blue LEDs compared to the other environments including greenhouse conditions. Phytochemical concentrations and a nutritive value of lettuce were also significantly affected by the light treatments. Chlorophyll and carotenoid concentrations increased in the plants grown under 70% red + 30% blue LEDs compared to those grown in the greenhouse. Vitamin C content was 2.25-fold higher in the plants grown under 100% blue LEDs compared to those grown in the greenhouse. Higher photosynthesis and maximal quantum yield of PSII photochemistry were also observed in the plants treated with LED lights. The application of LED light led to the elevated concentrations of macro-and micronutrients in lettuce possibly because of the direct effect of LED light and lower stress conditions in the growth chambers compared to the greenhouse. Although the mechanism of the changes in lettuce grown under LED is not well understood, the results of this study demonstrated that LED light could be used to enhance the growth and nutritional value of lettuce in indoor plant production facilities.     

Comparative proteomics analysis of the effect of combined red and blue lights on sugarcane somatic embryogenesis

Sugarcane is a renewable energy source that provides an alternative to fossil fuels and somatic embryogenesis can improve plant breeding for this purpose. Sugarcane somatic embryo development involves several unknown biochemical and molecular processes, and shotgun proteomics analysis may be helpful for the identification of somatic embryo-related proteins. The aims of this study were to evaluate the influence of combinations of red and blue wavelengths from LED lamps on the maturation of somatic embryos of sugarcane cv. SP80-3280 and to identify proteins that might be associated with the morphogenetic response. Embryogenic callus were subjected to maturation treatments with various combinations of red and blue wavelengths, and a fluorescent lamp was used as a control. The W_mB_dR_fR (450/530/660/735 nm) treatment for 28 days yielded 58 somatic embryos per callus, whereas the control yielded 23 somatic embryos per callus. Samples from the control and W_mB_dR_fR treatments were subjected to shotgun proteomic analysis and the proteomics data were processed with Progenesis QI software against the SUCEST project database. The quantitative shotgun proteomics analysis identified 1171 proteins common to the fluorescent and W_mB_dR_fR treatments, and of these 39 and 38 proteins were up-regulated and down-regulated, respectively, in the W_mB_dR_fR compared with the fluorescent treatment. The W_mB_dR_fR treatment induced a higher abundance of methyltransferases and clathrin heavy chain 1, which are related to differentiation and dedifferentiation processes and might be candidate markers for sugarcane somatic embryogenesis. Overall, our data indicate that LEDs can be advantageous substitutes for fluorescent lamps and that a combination of red and blue lights can enhance somatic embryo maturation and conversion in sugarcane.     

Effect of light emitting diodes on the cultivation of Spirulina platensis using NPK‐10:26:26 complex fertilizer

NPK‐10:26:26 complex fertilizer based culture medium was studied for the mass production of Spirulina platensis using different light emitting diodes (LEDs). First, cultivation was carried out under white LED to formulate the optimum fertilizer loading for which Spirulina growth was maximized. Optimum composition for newly formulated fertilizer medium was NPK fertilizer ?0.76 g L^?1 and sodium bicarbonate ?10.0 g L^?1 and corresponding biomass productivity was found to be 76.67 mg L^?1 day^?1. The effect of different LEDs (for example, blue, white, red, green and yellow) on Spirulina growth kinetics and the accumulation of chlorophyll, protein and lipid content was determined using the optimum NPK fertilizer medium. Kinetic parameters (i.e., biomass productivity, maximum specific growth rate, maximum biomass concentration, nitrogen‐to‐biomass conversion factor and phosphorus‐to‐biomass conversion factor) and chlorophyll accumulation were affected by the use of different LEDs and follow the following trend: blue > white > red > green > yellow, whereas protein and lipid accumulation was almost independent of LEDs used. Elemental C, N, P and K concentrations were measured to find the effects of nutrients for the growth of Spirulina platensis. Physicochemical parameters (pH and conductivity) were also monitored during biomass growth under different LEDs. Finally, biomass growth using NPK‐10:26:26 fertilizer under different LEDs was compared with standard Zarrouk medium and better growth results were obtained using optimally formulated NPK‐10:26:26 fertilizer medium.     

Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes (LEDs) with and without supplemental blue lighting

Red light-emitting diodes (LEDs) are a potential light sourcefor growing plants in spaceflight systems because of their safety,small mass and volume, wavelength specificity, and longevity.Despite these attractive features, red LEDs must satisfy requirementsfor plant photosynthesis and photomorphogenesis for successfulgrowth and seed yield. To determine the influence of galliumaluminium arsenide (GaAIAs) red LEDs on wheat photomorphogenesis,photosynthesis, and seed yield, wheat (Triticum aestivum L.,cv. ‘USU-Super Dwarf’) plants were grown under redLEDs and compared to plants grown under daylight fluorescent(white) lamps and red LEDs supplemented with either 1% or 10%blue light from blue fluorescent (BF) lamps. Compared to whitelight-grown plants, wheat grown under red LEDs alone demonstratedless main culm development during vegetative growth throughpreanthesis, while showing a longer flag leaf at 40 DAP andgreater main culm length at final harvest (70 DAP). As supplementalBF light was increased with red LEDs, shoot dry matter and netleaf photosynthesis rate increased. At final harvest, wheatgrown under red LEDs alone displayed fewer subtillers and alower seed yield compared to plants grown under white light.Wheat grown under red LEDs+10% BF light had comparable shootdry matter accumulation and seed yield relative to wheat grownunder white light. These results indicate that wheat can completeits life cycle under red LEDs alone, but larger plants and greateramounts of seed are produced in the presence of red LEDs supplementedwith a quantity of blue light. Key words: Triticum aestivum L., red light, blue light, subtillering, bioregenerative advanced life support     

Influence of light quality and photoperiod on flowering of Cyclamen persicum Mill. cv. ‘Dixie White’

The effect of light quality (spectral quality) and photoperiod (day length) were studied on flowering of Cyclamen persicum cv. Dixie White. Light generated from light emitting diodes (LED) i.e. monochromatic blue (10 or 12 h per day), monochromatic red (10 or 12 h per day), blue plus red (10 or 12 h per day) and fluorescent lights were used in these studies. It was found that blue plus red LEDs improved flower induction in cyclamen, the number flower buds and open flowers being highest in the plants grown under blue plus red LED (10 h per day). Blue and red LEDs alone reduced the flowering response. Peduncle length (flower stalk length) and blooming period of flowers were also influenced by light qualities and photoperiod treatments. Peduncle length was 23.8 cm on plants grown under red LED (12 h per day) treatment but 14 cm on plants grown under fluorescent light. Blooming period of flowers grown under fluorescent light was 20 d, whereas it was 40 d with the plants grown under red LEDs (10 h per day). The results indicate that flowering and subsequent growth of cyclamen can be controlled by manipulating light quality and lighting period.     

Internally illuminated photobioreactor using a novel type of light-emitting diode (LED) bar for cultivation of <Emphasis Type="Italic">Arthrospira platensis</Emphasis>

The biochemical properties of Spirulina platensis in an internally illuminated photobioreactor (IlPBR) were investigated under different light-emitted diode (LED) wavelengths; blue (λ_max= 450 and 460 nm), green (λ_max= 525 nm), red (λ_max = 630 and 660 nm), and white (6,500K), with various light intensities (200, 500, 1,000, and 2,000 μmol/m²/sec) were examined. The highest specific growth rate, maximum biomass, and phycocyanin productivity occurred under the red LEDs (0.39/day, 0.10 g/L/day, and 0.14 g/g-cell/day, respectively) at 1,000 μmol/m²/sec; the lowest growth rate was obtained under blue LEDs. Indeed, the size of trichomes was changed into short form under blue LEDs at all light intensities or all LEDs at 2,000 μmol/m²/sec for the first 2 days after inoculation, and S. platensis did not grow in the IlPBR under the dark condition. These results provide a base for different approaches for designing the pilot scale photobioreactor and developing cost-effective light sources.     

Blue and red light-emitting diodes with or without sucrose and ventilation affect in vitro Growth ofRehmannia glutinosa plantlets

Single-node, in vitro cuttings ofRehmannia glutinosa were transplanted to MS basal media and grown for 30 d. Plantlets were grown under various culture conditions: four different light qualities (red LEDs, blue LEDs, mixed LEDs, and fluorescent); with sucrose (30 mg.L^-1) or without (0 mg.L^-1); with air exchanges (3.5 h.^-1) or without (0.1 h.L^-1). Highest dry weights were obtained from plantlets under blue LEDs with 3.5h.L^-1 air exchanges. Light source did not affect shoot elongation in ventilated conditions, but without ventilation, the shoots of plantlets under red LEDs were twice as long as for plantlets growing under other types of lighting. Plantlets grown without sucrose showed little difference in photosynthesis under any of the tested light qualities. In contrast, the photosynthetic rate of those in the sucrose-containing media varied according to light source.     

Enhanced algae growth in both phototrophic and mixotrophic culture under blue light

Biomass productivity and fatty acid methyl esters (FAME) derived from intracellular lipid of a Nannochloropsis sp. isolated from Singapore’s coastal waters were studied under different light wavelengths and intensities. Nannochloropsis sp., was grown in both phototrophic and mixotrophic (glycerol as the carbon source) culture conditions in three primary monochromatic light wavelengths, i.e., red, green and blue LEDs, and also in white LED. The maximum specific growth rate (μ) for LEDs was blue > white > green > red. Nannochloropsis sp. achieved a μ of 0.64 and 0.66 d⁻¹ in phototrophic and mixotrophic cultures under blue lighting, respectively. The intracellular fatty acid composition of Nannochloropsis sp. varied between cultures exposed to different wavelengths, although the absolute fatty acid content did differ significantly. Maximum FAME yield from Nannochloropsis sp. was 20.45% and 15.11% of dry biomass weight equivalent under photo- and mixotrophic culture conditions respectively for cultures exposed to green LED (550 nm). However, maximum volumetric FAME yield was achieved for phototrophic and mixotrophic cultures (i.e., 55.13 and 111.96 mg/l, respectively) upon cell exposure to blue LED (470 nm) due to highest biomass productivity. It was calculated that incremental exposure of light intensity over the cell growth cycle saves almost 20% of the energy input relative to continuous illumination for a given light intensity.     

Effects of light quality on growth and development of protocorm-like bodies of <Emphasis Type="Italic">Dendrobium officinale</Emphasis> in vitro

The effect of light quality on protocorm-like bodies (PLBs) of Dendrobium officinale was investigated. PLBs of D. officinale were incubated under a number of different light conditions in vitro, namely: dark conditions; fluorescent white light (Fw); red light-emitting diodes (LEDs); blue LEDs; half red plus half blue [RB (1:1)] LEDs; 67% red plus 33% blue [RB (2:1)] LEDs; and 33% red plus 67% blue [RB (1:2)] LEDs. Growth parameters, number of shoots produced per PLB, chlorophyll concentration and carotenoid concentration were measured after 90 days culture. The percentage of PLBs producing shoots was 85% under blue LEDs. In contrast, the percentage of PLBs producing shoots was less than 60% under dark conditions, fluorescent white light and red LEDs. The number of shoots produced per PLB was more than 1.5 times greater under blue LEDs, RB (1:1) LEDs and RB (1:2) LEDs than those cultured under other light treatments [dark, Fw, red LEDs and RB (2:1)]. Chlorophyll and carotenoid concentrations were significantly higher under blue LEDs and different red plus blue LED ratios, compared to other light treatments (dark, Fw and red LEDs). Blue LEDs, Fw, and RB (1:2) LEDs produced higher dry matter accumulations of PLBs and shoots. This study suggests that blue LEDs or RB (1:2) LEDs could significantly promote the production of shoots by protocorm-like bodies of D. officinale and increase the dry matter of PLBs and the accumulation of shoot dry matter in vitro.     

Usability of time-lapse digital camera images to detect characteristics of tree phenology in a tropical rainforest

We evaluated the usability of the red (R), green (G), and blue (B) digital numbers (DN_RGB) extracted from daily phenological images of a tropical rainforest in Malaysian Borneo. We examined temporal patterns in the proportions of DN_R, DN_G, and DN_B as percentages of total DN (denoted as %R, %G and %B), in the hue, saturation, and lightness values in the HSL color model, and in a green excess index (GEI) of the whole canopy and of individual trees for 2 years. We also examined temporal patterns in the proportions of the red, green, and blue reflectance of the whole canopy surface as percentages of total reflectance (denoted as %ref_R, %ref_G, and %ref_B), and vegetation indices (the normalized-difference vegetation index, enhanced vegetation index, and green–red vegetation index) of the whole canopy by using daily measurements from quantum sensors. The temporal patterns of %RGB and saturation of individual trees revealed the characteristics of tree phenology caused by flowering, coloring, and leaf flushing. In contrast, those of the whole canopy did not, nor did those of %ref_R, %ref_G, or %ref_B, or the vegetation indices. The temporal patterns of GEI, however, could detect differences among individual trees caused by leaf flushing and coloring. Our results show the importance of installing multiple time-lapse digital cameras in tropical rainforests to accurately evaluate the sensitivity of tree phenology to meteorological and climatic changes. However, more work needs to be done to adequately describe whole-canopy changes.     

LED light for in vitro and ex vitro efficient growth of economically important highbush blueberry (<Emphasis Type="Italic">Vaccinium corymbosum</Emphasis> L.)

Light-emitting diodes (LEDs) are useful for the growth of many plants, but not known for blueberry species. This study examined the effects of fluorescent lamps and 100 % red, 80 % red plus 20 % blue, 50 % red plus 50 % blue, and 100 % blue LEDs on the growth and development of highbush blueberry shoots under aseptic and non-aseptic conditions. Results revealed that monochromatic blue LEDs accumulated the highest contents of leaf chlorophylls. In contrast, monochromatic red LEDs inhibited chlorophyll accumulation, but produced the longest shoots and roots and provided high percentages of side shoot formation from ex vitro plants. Mixed LEDs, particularly 50 % red plus 50 % blue light, improved plant growth with respect to notably increased shoot and root biomass. Direct rooting of in vitro shoots under non-aseptic conditions was readily achieved using a commercial mixture of perlite and peat moss with high humidity controls. These findings obviously suggest the efficient use of LEDs to replace traditional fluorescent lamps in large-scale propagation of the highbush blueberry, and also pave the way for future studies on LEDs for standardizing micropropagation protocols to shrub crops and woody plants.     

Does Lighting Manipulation During Incubation Affect Hatching Rhythms and Early Development of Sole?

Light plays a key role in the development of biological rhythms in fish. Previous research on Senegal sole has revealed that both spawning rhythms and larval development are strongly influenced by lighting conditions. However, hatching rhythms and the effect of light during incubation are as yet unexplored. Therefore, the aim of this study was to investigate the impact of the light spectrum and photoperiod on Solea senegalensis eggs and larvae until day 7 post hatching (dph). To this end, eggs were collected immediately after spawning during the night and exposed to continuous light (LL), continuous darkness (DD), or light-dark (LD) 12L:12D cycles of white light (LD_W), blue light (LD_B; λ_peak?=?463?nm), or red light (LD_R; λ_peak?=?685?nm). Eggs exposed to LD_B had the highest hatching rate (94.5%?±?1.9%), whereas LD_R and DD showed the lowest hatching rate (54.4%?±?3.9% and 48.4%?±?4.2%, respectively). Under LD conditions, the hatching rhythm peaked by the end of the dark phase, but was advanced in LD_B (zeitgeber time 8 [ZT8]; ZT0 representing the onset of darkness) in relation to LD_W and LD_R (ZT11). Under DD conditions, the same rhythm persisted, although with lower amplitude, whereas under LL the hatching rhythm split into two peaks (ZT8 and ZT13). From dph 4 onwards, larvae under LD_B showed the best growth and quickest development (advanced eye pigmentation, mouth opening, and pectoral fins), whereas larvae under LD_R and DD had the poorest performance. These results reveal that developmental rhythms at the egg stage are tightly controlled by light characteristics, underlining the importance of reproducing their natural underwater photoenvironment (LD cycles of blue wavelengths) during incubation and early larvae development of fish. (Author correspondence: borja@um.es)     

Study of the beneficial effects of green light on lettuce grown under short‐term continuous red and blue light‐emitting diodes

Red and blue light are the most important light spectra for driving photosynthesis to produce adequate crop yield. It is also believed that green light may contribute to adaptations to growth. However, the effects of green light, which can trigger specific and necessary responses of plant growth, have been underestimated in the past. In this study, lettuce (Lactuca sativa L.) was exposed to different continuous light (CL) conditions for 48 h by a combination of red and blue light‐emitting diodes (LEDs) supplemented with or without green LEDs, in an environmental‐controlled growth chamber. Green light supplementation enhanced photosynthetic capacity by increasing net photosynthetic rates, maximal photochemical efficiency, electron transport for carbon fixation (J_PSII) and chlorophyll content in plants under the CL treatment. Green light decreased malondialdehyde and H₂O₂ accumulation by increasing the activities of superoxide dismutase (EC 1.15.1.1) and ascorbate peroxidase (EC 1.11.1.11) after 24 h of CL. Supplemental green light significantly increased the expression of photosynthetic genes LHCb and PsbA from 6 to 12 h, and these gene expressions were maintained at higher levels than those under other light conditions between 12 and 24 h. However, a notable downregulation of both LHCb and PsbA was observed during 24 to 48 h. These results indicate that the effects of green light on lettuce plant growth, via enhancing activity of particular components of antioxidative enzyme system and promoting of LHCb and PsbA expression to maintain higher photosynthetic capacity, alleviated a number of the negative effects caused by CL.     

Growth of Tsuru-rindo (Tripterospermum japonicum) culturedin vitro under various sources of light-emitting diode (LED) irradiation

We studied the effects of light generated by LEDs on the growth of Tsururindo (Tripterospermum japonicum) shoots. Apical shoots (2–3 cm long) were cultured on MS basal media supplemented with 3% sucrose, and were maintained for four weeks under five different light qualities: F (fluorescent lamp), red LED (R), 70% red + 30% blue LED (R7B3), 50% red + 50% blue (R5B5), or blue LED (B). Rooting was promoted by red light (100%) but was inhibited by blue light. Plant growth, as defined by root number, fresh weight, and chlorophyll content, was generally healthier for cultures irradiated with mixed LEDs, and was the best under R7B3. Ventilation resulted in more rapid apical shoot growth and rooting compared with control plants, when both were treated with the R7B3 system. We demonstrated here that plant growth can be controlled by using LEDs to adjust for the most effective irradiation conditions, compared with the performance observed when conventional fluorescent lamps are utilized.     

Light emitting diodes increase phenolics of buckwheat (Fagopyrum esculentum) sprouts

Abstract

Four types of light emitting diodes (LEDs) were used in three combinations (all blue [BBB], red: blue: far-red [RBFr]=4:1:1 and red: green: blue [RGB]=4:1:1) and seven irradiation cycles (12 h/12 h photoperiod, 1 Hz, 10 Hz, 100 Hz, 1 KHz, 10 KHz and 100 KHz) were applied to examine their effect on growth, stem color and phenolic compounds (homoorientin, orientin, rutin, vitexin and isovitexin) in buckwheat (Fagopyrum esculentum cv. Great Ruby) sprouts. With a few exceptions, among all the combinations and irradiation cycles of LEDs, the Great Ruby cultivar showed significant differences in total height and dry weight of sprouts. The study revealed that there was a direct effect of different combination and irradiation cycles of LEDs on sprout height and dry weight; and among the combinations, RBFr and BBB had more positive effect than RGB. Increasing irradiation cycles markedly decreased the red color of stalks of F. esculentum cv. Great Ruby sprouts, with no significant effect on leaf color. In sprouts, the rutin content of leaves and stalks was higher at 12 h photoperiod and the amount in leaves was 5–7% higher than that of stalks in all combinations and irradiation cycles of LEDs. Among polyphenols, the rutin content in stalks was 1.45–2.97 mg g^?1 dry weight and the maximum amount of rutin was obtained from RGB combination of LEDs. In leaves, higher amounts of homoorientin, orientin and vitexin+isovitexin were obtained from the RGB combination and there were significant differences between RGB and other two combinations of LEDs. On the other hand, in between the irradiation cycles used in the study, there were no significant differences for other polyphenols in leaves and stalks of buckwheat sprouts.     

Controllable spectrum artificial sunlight source system using LEDs with 32 different peak wavelengths of 385-910 nm

This study developed a lighting system that produces an approximate spectral irradiance (SI) of ground level sunlight in the wavelength range of 385–910 nm (GLS_385–910) using 547 light‐emitting diodes (LEDs) with 32 different peak wavelengths. The produced SI can be modified over an arbitrary wavelength band. The SI at the light outlet reached up to 1/2 of the GLS_385–910 of a sunny April day, although the produced SI deviated from the GLS_385–910 at some wavelengths. For subsequent experiments, the reference SI was defined as 1/4 GLS_385–910 of a sunny April day. The SI produced from the lighting system was adjusted to approximate the reference SI. The ratios of the produced SI and the reference SI were within 0.72–1.28. As an application of the lighting system for biological studies, the transmitted SI of a green leaf of perilla (Perilla frutescens L.) was investigated. The curve shape of the transmitted SI, which had characteristically low transmission percentages of blue and red light, reflected the characteristics of the absorption spectra of chlorophylls. The lighting system is therefore potentially beneficial for use in diagnosing physiological conditions of plant leaves, although its application is not limited to plant physiological studies. Bioelectromagnetics 32:243–252, 2011. © 2010 Wiley‐Liss, Inc.