NaCl and light quality reprogram carbohydrate metabolism to modulate growth, quality, and flavor in mustard (Brassica juncea) sprouts.

The mechanisms by which different light spectra regulate plant shoot elongation vary, and phytohormones respond differently to such spectrum-associated regulatory effects. Light supplementation can effectively control seedling growth in Norway spruce. However, knowledge of the effective spectrum for promoting growth and phytohormone metabolism in this species is lacking. In this study, 3-year-old Norway spruce clones were illuminated for 12 h after sunset under blue or red light-emitting diode (LED) light for 90 d, and stem increments and other growth traits were determined. Endogenous hormone levels and transcriptome differences in the current needles were assessed to identify genes related to the red and blue light regulatory responses. The results showed that the stem increment and gibberellin (GA) levels of the seedlings illuminated by red light were 8.6% and 29.0% higher, respectively, than those of the seedlings illuminated by blue light. The indoleacetic acid (IAA) level of the seedlings illuminated by red light was 54.6% lower than that of the seedlings illuminated by blue light, and there were no significant differences in abscisic acid (ABA) or zeatin riboside [ZR] between the two groups of seedlings. The transcriptome results revealed 58,736,166 and 60,555,192 clean reads for the blue-light- and red-light-illuminated samples, respectively. Illumina sequencing revealed 21,923 unigenes, and 2744 (approximately 93.8%) out of 2926 differentially expressed genes (DEGs) were found to be upregulated under blue light. The main KEGG classifications of the DEGs were metabolic pathway (29%), biosynthesis of secondary metabolites (20.49%) and hormone signal transduction (8.39%). With regard to hormone signal transduction, AUXIN-RESISTANT1 (AUX1), AUX/IAA genes, auxin-inducible genes, and early auxin-responsive genes [(auxin response factor (ARF) and small auxin-up RNA (SAUR)] were all upregulated under blue light compared with red light, which might have yielded the higher IAA level. DELLA and phytochrome-interacting factor 3 (PIF3), involved in negative GA signaling, were also upregulated under blue light, which may be related to the lower GA level. Light quality also affects endogenous hormones by influencing secondary metabolism. Blue light promoted phenylpropanoid biosynthesis, phenylalanine metabolism, flavonoid biosynthesis and flavone and flavonol biosynthesis, accompanied by upregulation of most of the genes in their pathways. In conclusion, red light may promote stem growth by regulating biosynthesis of GAs, and blue light may promote flavonoid, lignin, phenylpropanoid and some hormones (such as jasmonic acid) which were related to plant defense in Norway spruce, which might reduce the primary metabolites available for plant growth.

SUMMARY The ultrastructure of the vegetative gametophytic cells of Porphyra leucosticta Thuret grown in red, blue and green light was studied both in ultrathin sections and in replicas of rapidly frozen cells. High activity of dictyosornes and mucilage sacs results in a dramatic decrease of the protoplasmic area and in thicker cell walls in red light in comparison with blue light and the control. There are numerous well-formed phycobili-somes in blue light, whereas not well-formed ones are present in red and especially in green light. There are also many phycobilisomes in the intrapyrenoidal thylakoids in blue light, fewer in green light, but they are absent in red light and in the control. It seems that in red and especially in green light, the phycobilisomes have fewer rods than in blue light. In green light, chloroplasts bear numerous genophores in contrast to blue and red light. The spacings of neighboring parallel thylakoids are as follows: control 64.3 nm, blue light 90.6 nm, red light 41.3 nm, green light 43.7 nm. Due to the relatively small spacing of the neighboring parallel thylakoids in red (41.3 nm) and in green light (43.7 nm) and of the given height of phycobilisomes (35 nm), the alternate phycobilisomes attached to neighboring lamellae are forced to interdigitate. The density of phycobilisomes per square micrometer of thylakoid surface dramatically increases in blue light (800 μm−2) in relation to red (250 μm−2) and green light (180 μm−2). The protoplasmic fracture face of the thylakoids reveals numerous, tightly packed, but randomly distributed particles. The particle size distribution is uniform in the two types of fracture faces, with an average diameter of about 11.5 nm. In blue light, both the phycobilisomes and exoplasmic face particles are organized into rows with a spacing of 60–70 nm. The results (changes: in the protoplasmic area; in the spacing of the thylakoids; in phycobilisome arrangement; in structure, shape and size of phycobilisomes; and in the accumulation of plastoglobuli), have shown that the monochromatic light (blue, red and green) brings about marked changes in the package effect and consequently in the efficiency of light absorption. In addition, the blue light contributes to the intense production of chlorophyll a, phycoerythrin, phycocyanin and soluble proteins, while intense production of polysaccharidic material is attributed to red light.

Red and blue light are the primary spectra absorbed by photosynthetic pigments in plants. Through the signal pathways mediated by phytochromes (PHY) and cryptochromes (CRY)/phototropins (PHOT), they coope-ratively regulate photosynthetic carbon assimilation, and plant growth and development. We reviewed the regulatory mechanisms of red and blue light on photosynthetic characteristics and plant growth and development. Red light activates chlorophyll synthesis genes (HEMA1, CHLH) through phytochrome B (PHYB), increases chlorophyll b content but inhibits carotenoid accumulation. Blue light upregulates genes such as PSY and PDS through cryptochromes1/2 (CRY1/2), and promotes carotenoid synthesis. The combination of red and blue light significantly enhances photosynthetic rate and electron transfer efficiency by optimizing the thickness of palisade/spongy tissue and stomatal conductance. Blue light can alleviate the photoinhibition of PSⅡinduced by red light, increasing the maximum photochemical efficiency (Fv/Fm) and actual photochemical efficiency (ΦPSⅡ) of PSⅡ. In terms of growth and development, red light promotes stem elongation through the PHY-auxin pathway but inhibits root activity, while blue light enhances root absorption area and inhibits hypocotyl elongation through the CRY-PIN3 signaling pathway. Red and blue light cooperatively regulate flowering time. Red light delays flowering through the PHYB-PHYL-CO protein complex, while blue light promotes flowering through the CRY2/CO-FT protein pathway. Combined blue and red light can extend the flowering period and improve the quality of floral organs. We reviewed the applications of red and blue light in multiple fields such as plant factories, accelerated breeding, factory seedling cultivation, and space breeding. Currently, it is necessary to analyze the molecular networks of cross-regulation of photoreceptors, establish multi-factor coupling models, and develop crop-specific light requirement databases. In the future, combined with gene editing and intelligent light control technologies, the photosynthesis-morphogenesis coordination mechanism should be optimized directionally to promote the development of facility agriculture towards high efficiency and intelligence, and to provide theoretical support and technical references for high light efficiency, high-quality cultivation, and high-yield breeding practices in modern agriculture.

Elongation growth mediated by blue light varies with light intensities and plant species: A comparison with red light in arugula and mustard seedlings

Abstract.The response of stomatal conductance to broadband blue and red light was measured in whole shoots of Scots pine and Sitka spruce, two species which have low stomatal sensitivity to CO2. In Scots pine, blue light was more than three times more effective than red light (on an incident quantum basis) in opening stomata, particularly at low quantum flux densities (<100μmiol m−2s−1). However, the apparent quantum yield of net CO2assimilation rate in blue light was only half that in red light. The contrasting effects of red and blue light on conductance and assimilation led to higher intercellular CO2concentrations (Ci) in blue light (up to 100 μmol mol−1higher) than in red light. Similar results were obtained with Sitka spruce shoots, though differences in the effectiveness of red and blue light were less marked. In both species, both red and blue light increased conductance in normal and CO2‐free air, indicating that neither red nor blue light exert effects through changes in Cior mesophyll assimilation. However, decreases in Cicaused increases in conductance in both red and blue light, suggesting that these direct effects of light are not wholly independent of CO2.

The effects of blue and red light color combinations on the growth and immune performance of juvenile steelhead trout, Oncorhynchus mykiss

Effect of LED light quality on respiratory metabolism and activities of related enzymes of Haliotis discus hannai

Red and blue light are traditionally believed to have a higher quantum yield of CO2 assimilation (QY, moles of CO2 assimilated per mole of photons) than green light, because green light is absorbed less efficiently. However, because of its lower absorptance, green light can penetrate deeper and excite chlorophyll deeper in leaves. We hypothesized that, at high photosynthetic photon flux density (PPFD), green light may achieve higher QY and net CO2 assimilation rate (An) than red or blue light, because of its more uniform absorption throughtout leaves. To test the interactive effects of PPFD and light spectrum on photosynthesis, we measured leaf An of “Green Tower” lettuce (Lactuca sativa) under red, blue, and green light, and combinations of those at PPFDs from 30 to 1,300 μmol⋅m–2⋅s–1. The electron transport rates (J) and the maximum Rubisco carboxylation rate (Vc,max) at low (200 μmol⋅m–2⋅s–1) and high PPFD (1,000 μmol⋅m–2⋅s–1) were estimated from photosynthetic CO2 response curves. Both QYm,inc (maximum QY on incident PPFD basis) and J at low PPFD were higher under red light than under blue and green light. Factoring in light absorption, QYm,abs (the maximum QY on absorbed PPFD basis) under green and red light were both higher than under blue light, indicating that the low QYm,inc under green light was due to lower absorptance, while absorbed blue photons were used inherently least efficiently. At high PPFD, the QYinc [gross CO2 assimilation (Ag)/incident PPFD] and J under red and green light were similar, and higher than under blue light, confirming our hypothesis. Vc,max may not limit photosynthesis at a PPFD of 200 μmol m–2 s–1 and was largely unaffected by light spectrum at 1,000 μmol⋅m–2⋅s–1. Ag and J under different spectra were positively correlated, suggesting that the interactive effect between light spectrum and PPFD on photosynthesis was due to effects on J. No interaction between the three colors of light was detected. In summary, at low PPFD, green light had the lowest photosynthetic efficiency because of its low absorptance. Contrary, at high PPFD, QYinc under green light was among the highest, likely resulting from more uniform distribution of green light in leaves.

Effect of light quality, including red light, blue light, white light, red and blue mixing light with 8:1, 8:2 and 8:3, on the growth characteristics and metabolite accumulation of chlorella pyrenoidosa was conducted based on light emitting diode (LED). Results showed that chlorella pyrenoidosa grew best under blue light, and the optical density, specific growth rate and biomass of chlorella pyrenoidosa was about 2.4, 0.10 d-1and 6.4 g·L-1, respectively, while the optical density of chlorella pyrenoidosa was between 1.0 and 1.7, specific growth rate was between 0.06-0.10 d-1and biomass was between 2.7 and 3.8 g·L-1under other light quality after 30 days of cultivation. The optical density, specific growth rate and biomass of chlorella pyrenoidosa was approximately 2.05 times, 1.33 times and 2.06 times under blue light than red light, respectively. Moreover, Red and blue mixing light was conducive to the synthesis of chlorophyll a and carotenoids of chlorella pyrenoidosa, and blue light could promote the synthesis of chlorophyll b. Chlorophyll a and carotenoids content of chlorella pyrenoidosa was 13.5 mg·g-1and 5.8 mg·g-1respectively under red and blue mixing light with 8:1, while it was 8.4 mg·g-1and 3.6 mg·g-1respectively under blue light. Red and blue mixing light was more conducive to protein and total lipid content per dry cell of chlorella pyrenoidosa. Protein and total lipid content was 489.3 mg·g-1and 311.2 mg·g-1under red and blue mixing light with 8:3, while it was 400.9 mg·g-1and 231.9 mg·g-1respectively under blue light.

To ascertain whether red light, known to enhance mitochondrial function, can blunt a blue light insult to ARPE19 cells in culture. Semi-confluent ARPE19 cells cultured in 10% FBS were subjected to various regimes of treatment with blue (465-475nm, 800lux, 26W/m2 ) and red (625-635nm, 950lux, 6.5W/m2 ) light, as well as with toxins that inactivate specific enzymes associated with mitochondrial oxidative phosphorylation. Cultures were then analysed for cell viability (MTT assay), mitochondrial status (JC-1), ROS formation, immunocytochemistry and the activation of specific proteins by electrophoresis/Western blotting. In addition, ARPE19 cells were cultured in polycarbonate membrane inserts in culture medium containing 1% FBS. Such cultures were exposed to cycles of red, blue or a combination of red and blue light for up to 6weeks. Culture medium was changed and the trans-epithelium membrane resistance (TER) of the inserts-containing cells was measured twice weekly. ARPE19 cells in culture are affected negatively when exposed to blue light. This is indicated by a loss of viability, a depolarization of their mitochondria and a stimulation of ROS. Moreover, blue light causes an up-regulation of HO-1 and phospho-p-38-MAPK and a cleavage of apoptosis inhibitory factor, proteins which are all known to be activated during cell death. All of these negative effects of blue light are significantly blunted by the red light administered after the blue light insult in each case. ARPE19 cell loss of viability and mitochondrial potential caused by toxins that inhibit specific mitochondrial enzyme complexes was additive to an insult delivered by blue light in each case. After a time, ARPE19 cells in culture express the tight junction protein ZO-1, which is affected by blue light. The development of tight junctions between ARPE19 cells grown in inserts reached a steady peak of resistance after about 40days and then increased very slightly over the next 40days when still in darkness. However, maximum resistance was significantly attenuated, when cultures were treated with cycles of blue light after the initial 40days in the dark and counteracted significantly when the blue light cycle insult was combined with red light. Blue light affects mitochondrial function and also the development tight junctions between ARPE19 cells, which results in a loss of cell viability. Importantly, red light delivered after a blue light insult is significantly blunted. These findings argue for the therapeutic use of red light as a noninvasive procedure to attenuate insults caused by blue light and other insults to retinal pigment epithelial cell mitochondria that are likely to occur in age-related macular degeneration.

BackgroundIn a number of gram-positive bacteria, including Listeria, the general stress response is regulated by the alternative sigma factor B (SigB). Common stressors which lead to the activation of SigB and the SigB-dependent regulon are high osmolarity, acid and several more. Recently is has been shown that also blue and red light activates SigB in Bacillus subtilis.Methodology/Principal FindingsBy qRT-PCR we analyzed the transcriptional response of the pathogen L. monocytogenes to blue and red light in wild type bacteria and in isogenic deletion mutants for the putative blue-light receptor Lmo0799 and the stress sigma factor SigB. It was found that both blue (455 nm) and red (625 nm) light induced the transcription of sigB and SigB-dependent genes, this induction was completely abolished in the SigB mutant. The blue-light effect was largely dependent on Lmo0799, proving that this protein is a genuine blue-light receptor. The deletion of lmo0799 enhanced the red-light effect, the underlying mechanism as well as that of SigB activation by red light remains unknown. Blue light led to an increased transcription of the internalin A/B genes and of bacterial invasiveness for Caco-2 enterocytes. Exposure to blue light also strongly inhibited swimming motility of the bacteria in a Lmo0799- and SigB-dependent manner, red light had no effect there.Conclusions/SignificanceOur data established that visible, in particular blue light is an important environmental signal with an impact on gene expression and physiology of the non-phototrophic bacterium L. monocytogenes. In natural environments these effects will result in sometimes random but potentially also cyclic fluctuations of gene activity, depending on the light conditions prevailing in the respective habitat.

Previous results had shown that vertically directed polarized red light orients the growth of horizontally growing chloronemas of Dryopteris filix mas (L.) Schott in either direction perpendicular to the plane of vibration, i. e. the electric vector. This polarotropic response has been investigated more closely. 1. The effect was measured in terms of angle formed during bending of preoriented chloronemas in response to a turn of the vibration plane by 50°. 2. The orientation perpendicular to the vibration plane occurs throughout the visible spectrum. The action spectrum in the visible region has two peaks: one around 665 nm and another one, about hundred times higher, in the blue. 3. From the action spectrum and other results it must be assumed that polarotropism in the blue and the red far-red region is mediated by two different pigment systems. 4. As had been previously shown, far-red reduces the width of the chloronemas as compared to red and dark. This effect is clearly visible in the region between 707 and 747 nm. Its intensity dependence parallels that of polarotropism by the same wavelengths, and on the basis of this observation and other data it may be assumed that both effects are mediated by the same pigment. 5. The morphogenetic response, that is the development of a prothallium from the chloronema in blue light requires much higher doses than the blue light polarotropic response and starts at intensities at which saturation of polarotropism has almost been reached. From this it is assumed that these effects are mediated by two different pigment systems. 6. Partially illuminated chloronema tips react by bending toward the side of the illuminated flank. This is the case in both red and blue light. 7. From the results with polarized light and partial illumination it is inferred that both blue and red light absorbing pigment molecules are dichroic and located close to or in the cell wall with their axes of maximum absorption parallel to the cell surface. 8. These results allow a detailed description of the optics which are responsible for the absorption gradient in phototropism by unpolarized red and blue light. The gradient is caused by the screening effect, the lens effect creating a by-passed subequatorial zone, and possibly by the orientation of the dichroic pigment molecules, all of them leading to a gradient with more absorption on the side facing the light. 9. By dropping rice starch grains on chloronema tips and following their position during positive phototropic bending it was determined that the tip curvature is caused by bulging of the inner rather than by increased growth of the outer side. Thus in polarotropism and positive phototropism the side that absorbs more light has the higher growth rate. 10. The effect of polarized red light is not reversed by subsequent polarized farred but is instead slightly increased. 11. Adaptation by red light reduces the sensitivity to polarized red, but enhances the effect of polarized far red light as compared to dark adaptation. 12. Adaptation by red light also reduces the sensitivity to polarized blue light. 13. Unpolarized far-red partially reverses the effect of red light adaptation on red light sensitivity. 14. Unpolarized far-red given after polarized red light reduces the effect of the latter. 15. Assuming that phytochrome controls the effect in the red and far-red, all results can be satisfactorily interpreted only if one assumes that the axis of maximum absorption of phytochrome turns by 90° during the transition of the red absorbing form (Pr) to the far red absorbing form (Pfr), leading to an orientation of the Pfr molecules perpendicular to the cell surface. 16. From the interaction between red and far-red and red and blue it is assumed that adaptation by red light consists of a saturation with Pfr as well as with intermediate products formed subsequently to Pfr. Only saturation with the latter would interfere with the blue light response. 17. Growth measurements together with other results indicate that although the average growth rate of the chloronemas does not change over several days, the growth rate of individual chloronemas shows considerable fluctuations, perhaps representing regular oscillations with periods of several hours duration.

Photosynthesis and respiration rates, pigment contents, CO2 compensation point, and carbonic anhydrase activity in Cyanidioschizon merolae cultivated in blue, red, and white light were measured. At the same light quality as during the growth, the photosynthesis of cells in blue light was significantly lowered, while under red light only slightly decreased as compared with white control. In white light, the quality of light during growth had no effect on the rate of photosynthesis at low O2 and high CO2 concentration, whereas their atmospheric level caused only slight decrease. Blue light reduced markedly photosynthesis rate of cells grown in white and red light, whereas the effect of red light was not so great. Only cells grown in the blue light showed increased respiration rate following the period of both the darkness and illumination. Cells grown in red light had the greatest amount of chlorophyll a, zeaxanthin, and β-carotene, while those in blue light had more phycocyanin. The dependence on O2 concentration of the CO2 compensation point and the rate of photosynthesis indicate that this alga possessed photorespiration. Differences in the rate of photosynthesis at different light qualities are discussed in relation to the content of pigments and transferred light energy together with the possible influence of related processes. Our data showed that blue and red light regulate photosynthesis in C. merolae for adjusting its metabolism to unfavorable for photosynthesis light conditions.

Mesona chinensis Benth (MCB) is an important Chinese herbal medicine. The plant factories might be one of the ways to solve the shortage of MCB supply. In this study, the MCB seedlings were treated under the red (R) and blue (B) lights in the plant factory. Results showed that the red light promoted the growth and development of MCB in comparison with the blue light. Under the red-light condition, the biomass, plant height, and root characteristics were significantly higher than those under blue-light condition, while the soil and plant analyzer development (SPAD) under the red-light treatment was significantly lower than that under the blue-light treatment. Red light also significantly promoted the content of soluble sugar and pectin of MCB compared with blue light. Transcriptome analysis showed that a total of 4,165 differentially expressed genes (DEGs) were detected including 2,034 upregulated and 2,131 downregulated. Of these, 1,112 DEGs including 410 upregulated and 702 downregulated genes were associated with 111 pathways. Moreover, a total of 8,723 differentially expressed transcription factors (TFs) were identified in R vs. B, and these TFs were distributed in 56 gene families. Metabonomic results revealed that a total of 184 metabolites and 99 differentially expressed metabolites (DEMs) (42 upregulated and 57 downregulated) were identified in the red- and blue-light treatments. Integrative analysis of transcriptome and metabolome unveiled that a total of 24 pathways included 70 compounds (metabolites) and were associated with 28 unigenes. In particular, these pathways included starch and sucrose metabolism, phenylpropanoid biosynthesis, cysteine and methionine metabolism, glycolysis/gluconeogenesis, and pentose and glucuronate interconversions. The unigenes included asparagine synthetase (AS), thymidine kinase (TK), alpha, alpha-trehalose-phosphate synthase (TPS), phosphatase IMPL1 (IMPL1), dihydroflavonol 4-reductase (D4R), and 4-coumarate-CoA ligase-like 6 (4CL6), bifunctional aspartokinase-homoserine dehydrogenase 1 (thrA), and abscisic acid 8′-hydroxylase 2 isoform X1 (ABA8). It was indicated that these pathways and genes might play important roles in the growth and development of MCB. This study laid a foundation for the future research of MCB.

This study investigated the effects of blue and red light on metabolites of nitrate, key enzymes, and the gene expression of key enzymes in pakchoi plants (Brassica campestris L. var. Suzhouqing). Plants were grown under three light quality treatments, namely, white light (W), red light (R) and blue light (B), at the same photosynthetic photon flux density (PPFD) of approximately 150 μmol m-2 s-1 for 48 hours of continuous illumination, and W was set as the control. The dynamics of net photosynthetic rate in pakchoi subjected to different light treatments were the same as the total chlorophyll contents: blue light > white light > red light. The nitrate reductase (NR) activity, nitrite reductase (NiR) activity, glutamine synthetase (GS) activity and glutamate synthase (GOGAT) activity were highest under blue light. Further, the expression levels of NR, NiR and GS genes were significantly higher under blue light. Under continuous illumination, the auxin content (IAA) in pakchoi leaves was highest under blue light, whereas the abscisic acid (ABA) content was highest under red light. In contrast, there was no significant effect for gibberellin (GA) under any type of light treatment.