Supplemental Red Light Research Articles

Flavonoid biosynthesis is differentially altered in detached and attached ripening bilberries in response to spectral light quality.

Light spectral quality is known to affect flavonoid biosynthesis during fruit ripening. However, the response of fruits to different light conditions, when ripening autonomously from the parent plant (detached), has been less explored. In this study, we analyzed the effect of light quality on detached and naturally ripening (attached) non-climacteric wild bilberry (Vaccinium myrtillus L.) fruits accumulating high amounts of anthocyanins and flavonols. Our results indicated contrasting responses for the accumulation of phenolic compounds in the berries in response to red and blue light treatments. For detached berries, supplemental blue light resulted in the highest accumulation of anthocyanins, while naturally ripening berries had elevated accumulation under supplemental red light treatment. Both red and blue supplemental light increased the expression levels of all the major structural genes of the flavonoid pathway during ripening. Notably, the key regulatory gene of anthocyanin biosynthesis, VmMYBA1, was found to express fivefold higher under blue light treatment in the detached berries compared to the control. The red light treatment of naturally ripening berries selectively increased the delphinidin branch of anthocyanins, whereas in detached berries, blue light increased other anthocyanin classes along with delphinidins. In addition, red and far-red light had a positive influence on the accumulation of flavonols, especially quercetin and myricetin glycoside derivatives, in both ripening conditions. Our results of differential light effects on attached and detached berries, which lacks signaling from the mother plant, provide new insights in understanding the light-mediated regulatory mechanisms in non-climacteric fruit ripening.

Light-dependent activation of HY5 promotes mycorrhizal symbiosis in tomato by systemically regulating strigolactone biosynthesis.

Light quality affects mutualisms between plant roots and arbuscular mycorrhizal fungi (AMFs), which modify nutrient acquisition in plants. However, the mechanisms by which light systemically modulates root colonization by AMFs and phosphate uptake in roots remain unclear. We used a range of approaches, including grafting techniques, protein immunoblot analysis, electrophoretic mobility shift assay, chromatin immunoprecipitation, and dual-luciferase assays, to unveil the molecular basis of light signal transmission from shoot to root that mediates arbuscule development and phosphate uptake in tomato. The results show that shoot phytochrome B (phyB) triggers shoot-derived mobile ELONGATED HYPOCOTYL5 (HY5) protein accumulation in roots, and HY5 further positively regulates transcription of strigolactone (SL) synthetic genes, thus forming a shoot phyB-dependent systemic signaling pathway that regulates the synthesis and accumulation of SLs in roots. Further experiments with carotenoid cleavage dioxygenase 7 mutants and supplementary red light confirm that SLs are indispensable in the red-light-regulated mycorrhizal symbiosis in roots. Our results reveal a phyB-HY5-SLs systemic signaling cascade that facilitates mycorrhizal symbiosis and phosphate utilization in plants. The findings provide new prospects for the potential application of AMFs and light manipulation to effectively improve nutrient utilization and minimize the use of chemical fertilizers and associated pollution.

INFLUENCE OF BLUE AND RED LEDs ON DEVELOPMENT AND NUTRITIVE VALUE OF PERILLA FRUTESCENS (L.) CULTIVATED IN CLIMATE CHAMBERS

In this study influence of supplemental blue and red LED lighting on growth, nutrient solution uptake and concentration of secondary metabolites was investigated. Perilla plants were cultivated in climate chambers, where main light was provided by fluorescent tubes with PPFD between 123-177 μmolm-2s-1. Additionally, blue and red LEDs were used, providing 11 μmolm-2s-1 or 12 μmolm-2s-1, respectively. Temperature was set on 24/19°C (day/night), relative air humidity on 64/56% (day/night), and day length was 16 hours. Results showed that small portion of supplemental blue light (~9%) increased fresh mass (FM), dry mass (DM), and nutrient solution uptake (NSU) up to 50.33%, 10.85% or 31.80%, respectively. Supplemental red light (~6%) increased nutrient solution uptake up to 23.56%, while fresh and dry mass were higher than control, but without statistical significance. Regarding nutritive value of Perilla, supplemental blue light significantly increased carotenoid concentration (Car) (+13.37%), but polyphenols (PP), anthocyanins (Anth) and flavonoid (Fl) concentrations did not differ from the control. In treatment with supplemental red light, only flavonoid concentration was significantly increased (+14.34%). Use of supplemental blue or red LEDs in closed systems with controlled conditions increase or tends to increase plants fresh mass, dry mass, nutrient solution uptake rate, as well as concentration of some secondary metabolites.

Site selective and enhanced luminescence of SrGe4O9:Mn4+ red phosphor via Ti4+ or Sn4+ codoped

Sn4+/Ti4+ co-doped SrGe4O9:Mn4+ deep red phosphors were synthesized via high temperature solid state method. The structure, morphology and photoluminescence properties were investigated by XRD, SEM and fluorescentspectrometer. The obtained samples exhibit strong deep red emission located at 660 nm under 430 nm excitation. The optimum concentration of Mn4+ was about 1.2 mol% and concentration quenching mechanism was related to d-d interaction. Co-doping of Ti4+ (Sn4+) enhanced emission intensity of SrGe4O9 by 22% (13%) due to the changed coordinationenvironment of Mn4+ and efficient energy transfer between Ti4+ (Sn4+) and Mn4+. Sn4+ may be substituted the Ge1 site and Ti4+ replaced the Ge2 site. The fabricated LED showed a white light with chromaticity coordinates (0.3429, 0.2941). The results indicated that site selective occurred and SrGe4O9:Mn4+, Ti4+ (Sn4+) have potential to supplementary red light and package white LEDs.

Supplementary Red light results in the earlier ripening of tomato fruit depending on ethylene production

In greenhouse tomato production, the lower canopy of tomato plants is often shaded by the neighbouring tomato plants. Supplementary lighting can be used to provide sufficient light energy for plants. Red light is regarded as the most efficient spectrum in supplementary lighting. Whether and how supplementary red light in the ambient of sunlight affect the ripening of tomato remain to be elucidated. In this research, the impacts of supplementary red light on tomato ripening were examined by comparing the impacts of supplementary red light on ripening-related regulators, ethylene synthesis, ethylene signaling, carotenoid synthesis and light signaling in Micro-Tom wild type tomato fruit and ripening-inhibitor (rin) mutant. Supplementary red light did not affect the fruit ripening of rin mutant, because the deficiency of SlRIN resulted in down-regulation of genes encoding ripening-related regulators and suppression of ethylene biosynthesis. The wild type tomato fruit under supplementary red light showed accelerated color transition during ripening, which was associated with the increased expressions of genes encoding ripening-related regulators and ethylene biosynthesis. The increased expressions of genes encoding phytochrome in wild type tomato fruit under supplementary red light might reduce the level of phytochrome-interacting factors, resulting in higher activation of the phytoene synthase and overaccumulation of phytoene. Supplementary red light in ambient sunlight resulted in the accumulation of phytoene and the earlier ripening in tomato fruit, which depended on ethylene production.

Adding Blue to Red Supplemental Light Increases Biomass and Yield of Greenhouse-Grown Tomatoes, but Only to an Optimum.

Greenhouse crop production in northern countries often relies heavily on supplemental lighting for year-round yield and product quality. Among the different spectra used in supplemental lighting, red is often considered the most efficient, but plants do not develop normally when grown solely under monochromatic red light (“red light syndrome”). Addition of blue light has been shown to aid normal development, and typical lighting spectra in greenhouse production include a mixture of red and blue light. However, it is unclear whether sunlight, as part of the light available to plants in the greenhouse, may be sufficient as a source of blue light. In a greenhouse high-wire tomato (Solanum lycopersicum), we varied the percentage of blue supplemental light (in a red background) as 0, 6, 12, and 24%, while keeping total photosynthetically active radiation constant. Light was supplied as a mixture of overhead (99 μmol m-2 s-1) and intracanopy (48 μmol m-2 s-1) LEDs, together with sunlight. Averaged over the whole experiment (111 days), sunlight comprised 58% of total light incident onto the crop. Total biomass, yield and number of fruits increased with the addition of blue light to an optimum, suggesting that both low (0%) and high (24%) blue light intensities were suboptimal for growth. Stem and internode lengths, as well as leaf area, decreased with increases in blue light percentage. While photosynthetic capacity increased linearly with increases in blue light percentage, photosynthesis in the low blue light treatment (0%) was not low enough to suggest the occurrence of the red light syndrome. Decreased biomass at low (0%) blue light was likely caused by decreased photosynthetic light use efficiency. Conversely, decreased biomass at high (24%) blue light was likely caused by reductions in canopy light interception. We conclude that while it is not strictly necessary to add blue light to greenhouse supplemental red light to obtain a functional crop, adding some (6–12%) blue light is advantageous for growth and yield while adding 24% blue light is suboptimal for growth.

Red Light-Dose or Wavelength-Dependent Photoresponse of Antioxidants in Herb Microgreens

The purpose of this study was to evaluate the role of 638-nm and 665-nm LEDs on changes of antioxidants of basil (Ocimum basilicum) and parsley (Petroselinum crispum), and to assess the effect of light quality on antioxidative status. Plants were grown in peat substrate for 19 days (21/17 ±2°C, 16 h). Experiments were performed in (I) a controlled-environment: B455,R638,R665,FR731(control); B455,R*638,R665,FR731; B455,R638,R*665,FR731; R638; R665 (B–blue, R- red, FR–far-red light). PPFD was set from 231 during growth, upto 300 μmol m-2 s-1 during 3-day treatment changing R638 or R665 PPFD level; in (II) greenhouse (November): high-pressure sodium lamps (HPS) (control—300 μmol m−2s−1); and HPS + 638 (HPS generated 90 and red LEDs—210 μmol m−2s−1). In general, under supplemental or increased red 638 nm light, amounts of tested antioxidants were greater in basil, whereas sole 665 nm or sole 638 nm is more favourable for parsley. Increased or supplemental red light significantly increased contents of phenolics, α-tocopherol, ascorbic acid and DPPH• but suppressed accumulation of lutein and β-carotene in basil, whereas an increase of β-carotene and DPPH• was observed in parsley. Hereby, the photoresponse of antioxidant compounds suggests that photoprotective mechanism is stimulated by both light-dose-dependent and wavelength-dependent reactions.

Impact of pre-harvest light spectral properties on health- and sensory-related compounds in broccoli florets.

Plants grown at different latitudes experience differences in light spectral composition. Broccoli (Brassica oleracea L. var italica) plants were grown in climate-controlled chambers under supplemental wavelengths (red, far-red, red + far-red or blue) from light-emitting diodes (LEDs). The light treatments were combined with two cold climate temperatures (12 and 15 °C) during broccoli head formation to investigate the effects on morphology and content of health- and sensory-related compounds: glucosinolates, flavonols, ascorbic acid and soluble sugars. Supplemental far-red and red + far-red light led to elongated plants and the lowest total glucosinolate content in broccoli florets. The content of quercetin was highest with supplemental red light. Vitamin C was not significantly affected by the light treatments, but 12 °C gave a higher content than 15 °C. The effects of supplemental red and far-red light suggest an involvement of phytochromes in the regulation of glucosinolates and flavonols. A shift in red:far-red ratio could cause changes in their content besides altering the morphology. The sugar and vitamin C content appears to be unaffected by these light conditions. Supplemental blue light had little effect on plant morphology and content of the health- and sensory related compounds.

Suppression of Cucumber Powdery Mildew by Supplemental UV-B Radiation in Greenhouses Can be Augmented or Reduced by Background Radiation Quality.

This study demonstrates that the spectral quality of radiation sources applied with ultraviolet-B (UV-B; background radiation) affects the suppression of cucumber powdery mildew (Podosphaera xanthii) by UV-B. Suppression provided by daily UV-B exposure of 1 W/m2 for 10 min was greatest in the presence of red light or by a complete lack of background light, and powdery mildew suppression was least in the presence of ultraviolet-A (UV-A) or blue radiation compared with plants exposed only to 16 h of daily natural light supplemented with high-pressure sodium lamps that supply broad-spectrum radiation with peaks in the yellow-orange region. Exposure of powdery mildew-inoculated plants to supplemental red light without UV-B, beginning at the end of the daylight period, also reduced disease severity; however, supplemental blue light applied in the same fashion had no effect. Daily application of UV-B at 1 W/m2 beginning on the day of inoculation significantly reduced the severity of powdery mildew to 15% compared with 100% severity on control plants. Maximum suppression of powdery mildew was observed following 15 min of exposure to UV-B (1.1% severity compared with 100% severity on control plants) but exposure time had to be limited to 5 to 10 min to reduce phytotoxicity. There was no additional disease suppression when plants were exposed to UV-B beginning 2 days prior to inoculation compared with plants exposed to UV-B beginning on the day of inoculation. UV-B inhibited germination, infection, colony expansion, and sporulation of P. xanthii. The results suggest that efficacy of UV-B treatments, alone or in combination with red light, against P. xanthii can be enhanced by exposure of inoculated plants to these wavelengths of radiation during the night, thereby circumventing the counteracting effects of blue light and UV-A radiation. The effect of UV-B on powdery mildew seemed to be directly upon the pathogen, rather than induced resistance of the host. Night exposure of plants to 5 to 10 min of UV-B at 1 W/m2 and inexpensive, spectral-specific, light-emitting diodes may provide additional tools to suppress powdery mildews of diverse greenhouse crops.

Effects of different light quality on growth, active ingredients and enzymes activities of Salvia miltiorrhiza

This study aimed to investigate the effects of different light quality on the growth, accumulation of active ingredients and enzymes activities of Salvia miltiorrhiza. The seedlings of S. miltiorrhiza were treated by different light quality, and relative parameters were measured. The data was statistically processed. Plant height was significantly decreased with supplemental blue light (WB), and the root length, root diameter, root fresh weight and root dry weight were significantly increased with supplemental red light (WR). Salvianolic acid B concentration in S. miltiorrhiza was highly increased by supplemental blue and red light, but tanshinone IIA concentration was not significantly affected by supplemental blue and red light. Enzymes activities of SOD, POD, PAL, TAT and PPO in S. miltiorrhiza were significant increased by supplemental blue light, and enzymes activities of POD, TAT and PPO were significant increased by supplemental red light. The root growth of S. miltiorrhiza was greatly promoted by supplemental red light (WR). Salvianolic acid B concentration in S. miltiorrhiza was highly increased by supplemental blue and red light. Enzymes activities of TAT and PPO in S. miltiorrhiza were significant increased by supplemental blue light and red light.

Consequences of LHC II deficiency for photosynthetic regulation in chlorina mutants of barley

The light-harvesting chlorophyll a/b proteins associated with PS II (LHC II) are often considered to have a regulatory role in photosynthesis. The photosynthetic responses of four chlorina mutants of barley, which are deficient in LHC II to varying degrees, are examined to evaluate whether LHC II plays a regulatory role in photosynthesis. The efficiencies of light use for PS I and PS II photochemistry and for CO2 assimilation in leaves of the mutants were monitored simultaneously over a wide range of photon flux densities of white light in the presence and absence of supplementary red light. It is demonstrated that the depletions of LHC II in these mutants results in a severe imbalance in the relative rates of excitation of PS I and PS II in favour of PS I, which cannot be alleviated by preferential excitation of PS II. Analyses of xanthophyll cycle pigments and fluorescence quenching in leaves of the mutants indicated that the major LHC II components are not required to facilitate the light-induced quenching associated with zeaxanthin formation. It is concluded that LHC II is important to balance the distribution of excitation energy between PS I and PS II populations over a wide range of photon flux densities. It appears that LHC II may also be important in determining the quantum efficiency of PS II photochemistry by reducing the rate of quenching of excitation energy in the PS II primary antennae.

Far-Red Light-Induced Changes in Intracellular Potentials of Spinach Mesophyll Cells

In green plants, the large bioelectric changes that photosynthetically active light stimulates make it difficult to observe electrical potential changes related to phytochrome photoconversion. As a first step towards distinguishing between photosynthetic and phytochrome effects, we showed that red light enhances far-red stimulated intracellular potential changes in spinach (Spinacia oleracea) leaf mesophyll cells.For a dark-adapted leaf, the response to far-red light increased during the first 10 to 30 exposures of 2.5 minutes, after which it was constant. The intracellular potential depolarized by an average of 0.3 millivolts during each 2.5-minute far-red light period, and returned to the resting value during each subsequent dark period. Continuous supplementary red light (at 1-5% of the fluence rate of the far-red light that stimulated the depolarizations) increased the response to far-red 2- to 3-fold. Supplementary red light did not amplify the response to alternating 702 nanometers light and dark periods. The Emerson enhancement effect thus does not seem to explain amplification of the response to 730 nanometers light by supplementary red light. This does not prove that photosynthetic pigments are not involved in some other way.

Influence of light intensity and photoperiod on frost-hardiness development in Douglas-fir seedlings

Effect of light intensity and photoperiod on frost-hardiness development in 2-year-old Douglas-fir seedlings was studied using an electrical conductivity method to assess stem hardiness. Hardiness increased with light intensity to 1000 ft-c at 7.5 °C, under both 8-h and 16-h photoperiods, after about 8 weeks. This response suggested photosynthesis was necessary for rapid hardening, as also did the more rapid hardening obtained under continuous light at 40 ft-c, compared with 8-h photoperiods of the same intensity. By contrast, short photoperiods enhanced the rate of hardening at a light intensity of 3000 ft-c and 500 ft-c (after 7 weeks), compared with long photoperiods. After 7 weeks plants under short photoperiods with supplementary red light hardened like plants under long photoperiods, but after 10 weeks this effect of red light was no longer apparent. Far-red light did not produce any effect. Evidently a certain amount of photosynthesis must be carried out by Douglas-fir seedlings for rapid development of hardiness, but, with sufficient light for this to occur, short photoperiods hasten hardening.