Light Spectral Quality Research Articles

Blue lighting combined with cold storage temperature can suppress gray mold in strawberry fruit

Cold storage is an optimal way of preventing quality deterioration in fruit crops, and this is exemplified by strawberries. However, Botrytis cinerea, the causal agent of gray mold, is cold-adaptive and can cause losses to cold-stored fruit. This study evaluated the regulatory effects of the spectral quality of light on the fungal growth in vitro, and the development of gray mold on postharvest strawberries at both ambient (21 ℃) and cold (4 ℃) temperatures. None of the light qualities tested (white, blue, green, or red) significantly affected colony growth of B. cinerea compared with the dark conditions in which they were tested at 21 ℃. In fungal cultures kept at 4 ℃, blue light significantly retarded colony expansion compared to other light conditions and darkness. Moreover, blue light and cold conditions can synergistically result in an increased number of septa, hyphal abnormality and intracellular vacuoles. An enhanced accumulation of reactive oxygen species (ROS) was also observed in fungal hypha exposed to blue light under cold conditions. Infection assay on strawberries demonstrated that blue light caused insignificant and significant suppressive effects at 21 ℃ and 4 ℃, respectively. In addition, blue-light caused significant weight loss in strawberries compared with all other treatments. Consequently, blue-light illumination under cold conditions may result in oxidative stress to the B. cinerea cells, thus preventing this cold-adaptive pathogen from causing unexpected deterioration in the stored fruit.

Benzoxazinoids Biosynthetic Gene Cluster Identification and Expression Analysis in Maize under Biotic and Abiotic Stresses.

Benzoxazinoids (BXs) are unique bioactive metabolites with protective and allelopathic properties in maize in response to diverse stresses. The production of BXs involves the fine regulations of BXs biosynthetic gene cluster (BGC). However, little is known about whether and how the expression pattern of BGC members is impacted by biotic and abiotic stresses. Here, maize BGC was systemically investigated and 26 BGC gene members were identified on seven chromosomes, for which Bin 4.00-4.01/4.03-4.04/7.02 were the most enriched regions. All BX proteins were clearly divided into three classes and seven subclasses, and ten conserved motifs were further identified among these proteins. These proteins were localized in the subcellular compartments of chloroplast, endoplasmic reticulum, or cytoplasmic, where their catalytic activities were specifically executed. Three independent RNA-sequencing (RNA-Seq) analyses revealed that the expression profiles of the majority of BGC gene members were distinctly affected by multiple treatments, including light spectral quality, low-temperature, 24-epibrassinolide induction, and Asian corn borer infestation. Thirteen differentially expressed genes (DEGs) with high and specific expression levels were commonly detected among three RNA-Seq, as core conserved BGC members for regulating BXs biosynthesis under multiple abiotic/biotic stimulates. Moreover, the quantitative real-time PCR (qRT-PCR) verified that six core conserved genes in BGC were significantly differentially expressed in leaves of seedlings upon four treatments, which caused significant increases in 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) content under darkness and wound treatments, whereas a clear decrease in DIMBOA content was observed under low-temperature treatment. In conclusion, the changes in BX metabolites in maize were regulated by BGC gene members in multiple stress presences. Therefore, the identification of key genes associated with BX accumulation under biotic/abiotic stresses will provide valuable gene resources for breeding maize varieties with enhanced capability to adapt to environmental stresses.

Effect of the Intensity and Spectral Quality of LED Light on Growth and Quality of Spinach Indoors

Effect of the Intensity and Spectral Quality of LED Light on Growth and Quality of Spinach Indoors

The operation of PEPCK increases light harvesting plasticity in C4 NAD-ME and NADP-ME photosynthetic subtypes: A theoretical study.

The repeated emergence of NADP-malic enzyme (ME), NAD-ME and phosphoenolpyruvatecarboxykinase (PEPCK) subtypes of C4 photosynthesis are iconic examples of convergent evolution, which suggests that these biochemistries do not randomly assemble, but are instead specific adaptations resulting from unknown evolutionary drivers. Theoretical studies that are based on the classic biochemical understanding have repeatedly proposed light-use efficiency as a possible benefit of the PEPCK subtype. However, quantum yield measurements do not support this idea. We explore this inconsistency here via an analytical model that features explicit descriptions across a seamless gradient between C4 biochemistries to analyse light harvesting and dark photosynthetic metabolism. Our simulations show that the NADP-ME subtype, operated by the most productive crops, is the most efficient. The NAD-ME subtype has lower efficiency, but has greater light harvesting plasticity (the capacity to assimilate CO2 in the broadest combination of light intensity and spectral qualities). In both NADP-ME and NAD-ME backgrounds, increasing PEPCK activity corresponds to greater light harvesting plasticity but likely imposed a reduction in photosynthetic efficiency. We draw the first mechanistic links between light harvesting and C4 subtypes, providing the theoretical basis for future investigation.

Impact of photon flux density and light spectral quality on biomass production and arbutin compound accumulation in Origanum majorana L. plantlets

Impact of photon flux density and light spectral quality on biomass production and arbutin compound accumulation in Origanum majorana L. plantlets

Far-red light and temperature interactively regulate plant growth and morphology of lettuce and basil

Both the spectral quality of light, particularly the ratio of red (R; 600–700 nm) to far-red light (FR; 700–800 nm), and temperature can regulate phytochrome activities, subsequently influencing plant growth and morphology. However, our understanding of how light quality and temperature interact to control phytochrome-mediated morphological responses is largely limited to hypocotyl elongation in Arabidopsis seedlings. In this study, we quantified the interactive effects between FR light and temperature on morphological traits of agronomic and horticultural significance in two crops with contrasting morphology and growth habits, lettuce (Lactuca sativa L.) ‘Rex’ and basil (Ocimum basilicum) ‘Genovese’. Plants were grown under blue (B), green (G), R, and FR LED light with three spectral treatments [B25G25R200 (0%FR), B25G25R175FR25 (10%FR), B25G25R150FR50 (20%FR); the subscript represents photon flux density in μmol m−2 s−1] and five temperature regimes [Day (℃)/Night (℃); 20/20, 24/24, 28/28, 20/28 (–DIF), 28/20 (+DIF); DIF represents differential day/night temperature]. Total photon flux density in each spectral treatment was 250 μmol m−2 s−1 (400–800 nm; 12-h photoperiod). As FR light percentage and temperature increased, leaf length and plant height increased in both species. However, the effects of FR light and temperature were interdependent. Specifically, the stimulative effects of FR light on extension growth generally diminished under warmer temperatures and in the –DIF treatment (20/28 ℃). Total leaf area increased with increasing FR percentage under 20/20 and 24/24 ℃ treatments in both lettuce and basil. However, under 28/28 ℃, increasing the FR percentage from 0% to 20% caused a decrease in lettuce leaf area while having no effect on basil leaf area. Similar to responses in total leaf area, dry biomass significantly increased with increasing FR percentage under cooler temperatures. Under warm temperature of 28/28 ℃, dry biomass decreased with increasing FR percentage in lettuce, whereas no significant difference was observed in basil. Due to the interaction between FR and temperature, phytochrome photoequilibrium (PPE) estimated from photoconversions alone was less predictive of plant morphology under varying temperature conditions. Those results indicate that light spectrum and temperature interactively regulate the activity of phytochromes, plant morphology, and subsequent plant growth in both lettuce and basil, and thus should be co-optimized in controlled environment crop production systems.

Impact of Colored Shade Nets on Biomass Production, Essential Oil Composition and Orientin and Isoorientin Content in Lippia gracilis Schauer.

The objective of this study was to evaluate the effect of ChromatiNet on vegetative growth, total antioxidant capacity, phenolic and essential oils (EOs) composition of Lippia gracilis. The plants were cultivated under full sunlight, black, blue and red ChromatiNet. The flavonoid content and antioxidant capacity were quantified spectrophotometrically. The C-glycosylflavone isomers (orientin and isoorientin) were isolated and identified by conventional spectroscopic techniques and measured using high-performance liquid chromatography-diode array detection. The EO was analysed by gas chromatography and gas chromatography-mass spectrometry. Environment influenced growth, total antioxidant capacity and phytochemical levels. Shoot dry weight, thymol, carvacrol and (E)-caryophyllene were favoured under red and black ChromatiNet. Root growth, EOs, caryophyllene oxide, p-cymene, flavonoids, orientin and isoorientin were favoured in sunlight. Growth and accumulation of EOs, flavonoids and photosynthetic pigments increased under blue ChromatiNet. Therefore, Lippia gracilis plants have plasticity related to the spectral quality of light and it cultivate depends of the phytochemicals of interest.

Light intensity and spectral quality modulation for improved growth kinetics and biochemical composition of Chlamydomonas reinhardtii.

Effective strategies to optimize algal growth and lipid productivity are critical for the sustainable production of biomass for various applications. Light management has emerged as a promising approach, but the intricate relationship between light intensity, spectral quality, and algal responses remains poorly understood. This study investigated the effects of different light qualities (blue, red-orange, and white-yellow) and intensities (45-305 μmol/m2·s) on Chlamydomonas reinhardtii. Red-orange light exhibited the highest promotion of biomass growth and lipid productivity, with specific growth rates of 1.968 (d-1) and biomass productivity of 0.284 (g/L/d) at 155 μmol/m2·s and 205 μmol/m2·s, respectively. Within the intensity range of 205 μmol/m2·s to 305 μmol/m2·s, lipid mass fractions ranged from 10.5% w/w to 11.0% w/w, accompanied by lipid concentrations ranging from 68.6mg/L to 74.9mg/L. Red-orange light positively influenced carbohydrate accumulation, while blue light promoted protein synthesis. These findings highlight the importance of optimizing light quality and intensity to enhance algal biomass productivity and manipulate biochemical composition. Understanding the complex relationship between light parameters and algal physiology will contribute to sustainable algal cultivation practices and the use of microalgae as a valuable bioresource.

Photoconverting nets affect plant growth and levels of antiviral glucoevatromonoside and total cardenolides in Digitalis mariana ssp. heywoodii (P. Silva and M. Silva) Hinz

Digitalis mariana ssp. heywoodii (P. Silva & M. Silva) Hinz is an important source of bioactive cardenolides, including the promising antiviral agent glucoevatromonoside (GEV). The influence of light on the contents of total cardenolides has been demonstrated for different species of Digitalis. This study evaluated the influence of light spectral quality on the vegetative growth and levels of photosynthetic pigments, total proteins, total cardenolides, and GEV in D. mariana ssp. heywoodii. The process of extraction and quantification of GEV was established using an analytical quality by design (AQbD) approach, applying experimental design and analytical validation. Seedlings were grown for 120 days under photoconverting nets with 50% shading in blue, red, and black colours and under full sun. The use of blue net, followed by red net, resulted in the highest contents of GEV, total cardenolides, proteins, photosynthetic pigments and dry matter in the plants, along with highest root length and leaf area. The advantage of using blue nets over full sun for cultivating D. mariana ssp. heywoodii, herein demonstrated, aggregates new information on the management of this subspecies and corroborates previous data reported for other Digitalis species.

Dynamic spectrum lighting impact on plant morphology and cannabinoid profile of medical and recreational cannabis – A novel leapfrog strategy towards shaping the future of horticulture lighting

It is well documented that the light is the main factor or one of the factors influencing plant growth and development. The role of light spectral quality in meeting the specific needs during a plant’s developmental stages (germination, vegetative and flowering) has not been well defined and investigated. The objective of this study was to investigate the impact of light spectral quality on the growth and yield of cannabis plants during different developmental stages. Cannabis plants were grown in a controlled environment with distinct light spectral quality treatments applied at different growth stages. The plants were monitored for morphological responses and cannabinoid content. This study evaluated the hypothesis that, just like the dietary needs of human beings change with age, plants' nutritional and lighting requirements change with their growth stage. Plants' metabolic responses can be triggered and maximized by giving them the right light spectrum and intensity as the plant undergoes the development phases of its cycle. The results showed that the dynamic spectrum lighting led to a 33 % increase in yield and significant improvement in cannabinoid content. These findings challenge the conventional belief that a fixed full-spectrum white light is optimal for plant growth and development. Furthermore, it is hypothesized that plant development stages can be divided into more than the existing three conventional stages. This optimization resulted in the highest yield and energy savings under the dynamic spectrum. These novel findings will have important implications in motivating plant scientists to go beyond the conventional norm and could pave the way for a paradigm shift towards dynamic spectrum lighting, thus taking a leapfrog jump in shaping the future of horticulture lighting.

Microstructure Engineered Photon‐Managing Films for Solar Energy to Biomass Conversion

AbstractConversion of solar energy into chemical energy through natural photosynthesis plays a crucial role in sustainable energy transformation, bioresource production, and CO2 biofixation. Nevertheless, the overall solar energy to chemical energy (biomass) conversion efficiency in the photosynthetic organisms is still unsatisfactory because of their inefficient utilization of solar light. Here, a photonic method to improve photosynthesis of a unicellular green microalga, Chlamydomonas reinhardtii, a photosynthetic organism model is reported. For this purpose, an easy‐to‐fabricate microphotonic film is developed to improve the spectral quality of solar light reaching the microalgae through photon management (i.e., simultaneous solar spectral conversion and directional fluorescent emission). This study demonstrates that the short‐term oxygen evolution rate and the long‐duration biomass production of microalgae in 200‐mL laboratory photobioreactors are enhanced by a factor of 38% and 54%, respectively. In 5000‐mL scaled‐up bubble column photobioreactors placed outdoor under natural sunlight and weather conditions, the biomass yield is improved by more than 20% when compared to the control experiments conducted in parallel in an optically clear bubble column photobioreactor. Based on such experimental observations, the work here demonstrates the potential of photon management for promoting the solar energy‐to‐biomass conversion process of microalgae and other photosynthetic organisms.

Spectral light quality regulates the morphogenesis, architecture, and flowering in pepper (Capsicum annuum L.).

Transparent plastic films with poor light transmittance seriously affect the mass composition of visible light in many greenhouses, which leads to the reduction of photosynthesis in vegetable crops. Understanding the regulatory mechanisms of monochromatic light in the vegetative and reproductive growth of vegetable crops is of great importance for the application of light-emitting diodes (LEDs) in the greenhouse. In this study, three monochromatic light treatments (red-, green- and blue-light) were simulated by using LEDs to explore light quality-dependent regulation from the stage of seedling to flowering in pepper (Capsicum annuum L.). The results showed that light quality-dependent regulation guides the growth and morphogenesis in pepper plants. Red- and blue-light played opposite roles in determining the plant height, stomatal density, axillary bud growth, photosynthetic characteristics, flowering time and hormone metabolism, while green light treatment resulted in taller plants and fewer branches, which was similar to the red-light treatment. The weighted correlation network analysis (WGCNA) based on mRNA-seq results revealed that the two modules named "MEred" and "MEmidnightblue" were positively correlated with red- and blue-light treatment, respectively, exhibiting high correlations with the traits such as plant hormone content, branching and flowering. Moreover, our results suggest that the light response factor ELONGATED HYPOCOTYL 5 (HY5) is essential for blue light-induced plant growth and development by regulating photosynthesis in pepper plants. Hence, this study uncovers crucial molecular mechanisms of how light quality determines the morphogenesis, architecture, and flowering in pepper plants, thus providing a basic concept of manipulating light quality to regulate pepper plant growth and flowering under greenhouse conditions.

New insights into light spectral quality inhibits the plasticity elongation of maize mesocotyl and coleoptile during seed germination.

The plastic elongation of mesocotyl (MES) and coleoptile (COL), which can be repressed by light exposure, plays a vital role in maize seedling emergence and establishment under adverse environmental conditions. Understanding the molecular mechanisms of light-mediated repression of MES and COL elongation in maize will allow us to develop new strategies for genetic improvement of these two crucial traits in maize. A maize variety, Zheng58, was used to monitor the transcriptome and physiological changes in MES and COL in response to darkness, as well as red, blue, and white light. The elongation of MES and COL was significantly inhibited by light spectral quality in this order: blue light > red light > white light. Physiological analyses revealed that light-mediated inhibition of maize MES and COL elongation was closely related to the dynamics of phytohormones accumulation and lignin deposition in these tissues. In response to light exposure, the levels of indole-3-acetic acid, trans-zeatin, gibberellin 3, and abscisic acid levels significantly decreased in MES and COL; by contrast, the levels of jasmonic acid, salicylic acid, lignin, phenylalanine ammonia-lyase, and peroxidase enzyme activity significantly increased. Transcriptome analysis revealed multiple differentially expressed genes (DEGs) involved in circadian rhythm, phytohormone biosynthesis and signal transduction, cytoskeleton and cell wall organization, lignin biosynthesis, and starch and sucrose metabolism. These DEGs exhibited synergistic and antagonistic interactions, forming a complex network that regulated the light-mediated inhibition of MES and COL elongation. Additionally, gene co-expression network analysis revealed that 49 hub genes in one and 19 hub genes in two modules were significantly associated with the elongation plasticity of COL and MES, respectively. These findings enhance our knowledge of the light-regulated elongation mechanisms of MES and COL, and provide a theoretical foundation for developing elite maize varieties with improved abiotic stress resistance.

Spectral light quality on the seabed matters for macroalgal community composition at the extremities of light limitation

AbstractCompromised light quantity on the seabed affects the composition and resilience of marine forests and the maintenance of ecosystem services. However, the response of macroalgal assemblages to changes in the quality (spectral composition) of light as compared to the quantity alone is poorly understood. Here, we bridge radiative transfer modeling and algal physiology to simulate the underwater light environment and explore macroalgal responses to spectral attenuation by various coastal water constituents. We considered three groups of macroalgal taxa (class Phaeophyceae and, phyla Chlorophyta and Rhodophyta) for which we developed a “synthetic envelope” of spectrally resolved action spectra using 1 million radiative simulations. We found that brown algae were more efficient at harvesting light across the whole spectrum at low attenuation (< 0.2 m−1) when depths were greater than 10 m, whereas green algae dominated shallower depths than 10 m for low to high attenuation values. Finally, red algae made best use of the available light at relatively higher attenuation values (> 0.2 m−1) and deeper depths. We also demonstrated that the brown and green algal taxa showed higher photosynthetic efficiencies when attenuation was dominated by particulate matter rather than by phytoplankton or detrital matter. Our results shed new light on the “Complementary Chromatic Adaptation” hypothesis by confirming that algal pigmentation matters under a subset of scenarios, particularly at the limits of light availability in coastal waters. This study paves the way for identifying competitive thresholds in macroalgal communities by using satellite‐derived ocean color products to identify regions and depths of potential optical transitions.

Spectral quality influence on in vitro morphophysiological responses of Eucalyptus dunnii Maiden and Eucalyptus grandis W.Hill ex Maiden × E. urophylla S.T.Blake

Background: In vitro growth and development of plants in the micropropagation stages are influenced by several factors, including the light spectral quality, which has shown important effects on the photomorphogenesis. The work aimed to evaluate the photomorphogenic effect of spectral qualities on in vitro culture of Eucalyptus dunnii and Eucalyptus grandis × E. urophylla. Methods: Six light spectral qualities (i.e., red, white, blue, yellow, purple, and green) on in vitro multiplication, elongation, and adventitious rooting stages were evaluated through analysis of variance followed by a Tukey’s test. Results: White spectral quality was most adequate for in vitro multiplication of Eucalyptus dunnii and Eucalyptus grandis × E. urophylla, as it resulted in less tissue oxidation, longer shoot length, and more buds per explant. Red, blue and yellow spectral qualities increased the chlorophyll a, chlorophyll b, and total chlorophyll (a+b) leaf contents of Eucalyptus dunnii. To promote in vitro elongation, white spectral quality was most suitable for Eucalyptus dunnii, and yellow for Eucalyptus grandis × E. urophylla, as these resulted in more shoot length and shoots per explant. Red, white, blue and purple spectral qualities increased the stomatal density of Eucalyptus dunnii; while the white and yellow were the better for Eucalyptus grandis × E. urophylla. To promote in vitro rooting, the white and yellow spectral qualities caused the best results for the Eucalyptus dunnii and Eucalyptus grandis × E. urophylla, with longer root length and more roots per explant. Eucalyptus dunnii showed reduced adventitious rooting, regardless of spectral quality. Conclusions: Light quality influence the morphophysiological responses of Eucalyptus in different stages of in vitro culture. Our results contribute to maximise the in vitro cloning of important eucalypts species.

Impact of Different Light Characteristics on the Growth and Lipid Content of Diatom <i>Phaeodactylum tricornutum</i> Transconjugant Strains

Light regulates important metabolic processes in microalgal cells, which can further impact the metabolism and the accumulation of biomolecules such as lipids, carbohydrates, and proteins. Different characteristics of light have been studied on various strains of the model diatom Phaeodactylum tricornutum, but not on transconjugant cells and information on wild-type strains is still limited. Therefore, we studied the impact of different light characteristics such as spectral quality, light intensity and light shift on the growth, and the composition in lipids and fatty acids of P. tricornutum cells to provide a comprehensive context for future applications. Initially, we tested the impact of spectral quality and light intensity on P. tricornutum transformed with an episomal vector (Ptev), harboring the resistance gene Sh ble. Results indicated that Ptev cells accumulated more biomass and overall lipids in spectral quality Red 1 (R1: 34% > 600 nm > 66%) more effectively as compared to Red 2 (R2: 8% > 600 nm > 92%). It was also detected that cell granularity was higher in R1 as compared to R2. Furthermore, by testing two light intensities 65 μmol·m-2·s-1 and 145 μmol·m-2·s-1 light, it was observed that 145 μmol·m-2·s-1 led to an increase in growth trend, total biomass and lipid content. Combining spectral qualities and light intensities, we show that the lipid accumulation raised by 2.8-fold. Studying the light intensity and spectral quality allowed us to optimize the light conditions to R1 spectral quality and light intensity 145 μmol·m-2·s-1. These initial results showed that red light R1 at 145 μmol·m-2·s-1 was the best condition for biomass and total lipids accumulation in Ptev cells. Next, we further combined these two-light optimizations with a third light characteristics, i.e. light shift, where the cultures were shifted during the early stationary phase to a different light environment. We studied Red light shift (Rs) to investigate how light condition variations impacted P. tricornutum transconjugants Ptev and with an episomal vector containing the reporter gene YFP (PtYFP). We observed that Rs induced growth and fatty acid eicosapentaenoic acid (EPA) in Ptev as compared to PtYFP. Altogether, the study shows that red light shift of R1 at 145 μmol·m-2·s-1 promoted biomass and total lipids accumulation in Ptev and PtYFP cells. The study provides a comprehensive approach to using different light characteristics with the aim to optimize growth and lipids, as well as to fatty acid production.

Stimulatory and inhibitory effects of light on Cereus repandus (Cactaceae) seed germination are strongly dependent on spectral quality

AbstractIn small seeds, light often promotes germination and longer-term exposure to darkness reduces light sensitivity. In cacti inhabiting harsh environments, a rapid response to light exposure is potentially advantageous for seedling establishment. We exposed dark-imbibed seeds of the cactus Cereus repandus to doses of red (RED) light and far-red (FR) light. The seeds exhibited positive photoblastism to RED light. Although the initial levels of germination varied between seed lots, the sensitivity to increasing the RED dose did not. As little as 5 min per day for 4 d was sufficient to saturate the light requirement for germination. The effects of RED light were reversed by FR exposure as long as the interval between RED and FR did not extend to 2 d, by which time the seeds had ‘committed’ to germinate. Dark incubation for 1–2 weeks prior to RED exposure reduced light sensitivity in two seed lots, such that RED only promoted around 20% germination. Phytochrome is assumed to mediate the reversibility of the RED:FR response. High sensitivity to light spectral quality suggests that seeds of C. repandus are able to germinate quickly in high-quality microsites, but seed burial or shading may commit the seeds to form a soil seed bank. The light characteristics of the germination trait in this species are typical of many small seeded species of the drylands.

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.

Far-Red Light Coordinates the Diurnal Changes in the Transcripts Related to Nitrate Reduction, Glutathione Metabolism and Antioxidant Enzymes in Barley.

Spectral quality, intensity and period of light modify many regulatory and stress signaling pathways in plants. Both nitrate and sulfate assimilations must be synchronized with photosynthesis, which ensures energy and reductants for these pathways. However, photosynthesis is also a source of reactive oxygen species, whose levels are controlled by glutathione and other antioxidants. In this study, we investigated the effect of supplemental far-red (735 nm) and blue (450 nm) lights on the diurnal expression of the genes related to photoreceptors, the circadian clock, nitrate reduction, glutathione metabolism and various antioxidants in barley. The maximum expression of the investigated four photoreceptor and three clock-associated genes during the light period was followed by the peaking of the transcripts of the three redox-responsive transcription factors during the dark phase, while most of the nitrate and sulfate reduction, glutathione metabolism and antioxidant-enzyme-related genes exhibited high expression during light exposure in plants grown in light/dark cycles for two days. These oscillations changed or disappeared in constant white light during the subsequent two days. Supplemental far-red light induced the activation of most of the studied genes, while supplemental blue light did not affect or inhibited them during light/dark cycles. However, in constant light, several genes exhibited greater expression in blue light than in white and far-red lights. Based on a correlation analysis of the gene expression data, we propose a major role of far-red light in the coordinated transcriptional adjustment of nitrate reduction, glutathione metabolism and antioxidant enzymes to changes of the light spectrum.

Interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga Saccharina japonica (Laminariales) from Hokkaido, Japan

The interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga, Saccharina japonica (var. japonica, Laminariales) from Hokkaido, Japan were examined using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. Assessment of maximum quantum yields (in darkness) and effective quantum yields (at 50 μmol photons m−2 s−1) at nine temperatures (4–36 °C, four increments) during 3-d culture indicated a temperature threshold at 24 °C, with early decline of maximum quantum yields at such temperature, which could probably be due to exhaustion of carbohydrate reserves by respiration in prolonged darkness. Unlike maximum quantum yields that was relatively stable through 4–20 °C, effective quantum yields under 50 μmol photons m−2 s−1 gradually declined at low temperatures, revealing light sensitivity under chilling temperatures. Chronic 6-h exposures under 200 (low) and 1000 (high) μmol photons m−2 s−1 at 4, 16, and 24 °C generated a significant decline in effective quantum yields at 4 °C under both irradiances; however, only treatments under low irradiance fully recovered after a subsequent 12-h dim light treatment. Moreover, post-dim light acclimation effective quantum yields of treatments at 16 and 24 °C under high irradiance returned to initial levels, suggesting accelerated photoinhibition at low temperature. Photosynthesis–irradiance responses at 16 °C under blue (450 nm), green (525 nm), red (660 nm), and white light (metal halide lamp) showed that the maximum photosynthetic output occurred under blue and white lights. The photoinhibitory sensitivity to chilling-light stress and the enhanced photosynthesis under blue light of S. japonica presented additional evidence of their physiological adaptation to cold-temperate subtidal waters.