Search Results (46)

Carbon dioxide (CO₂) emissions due to human activities are responsible for approximately 80% of the drivers of global warming, resulting in a 1.1 °C increase above pre-industrial temperatures. This study quantified the CO₂ assimilation and productivity of the brown macroalgae Lessonia spicata in the central Pacific coast of Chile, across seasonal and daily cycles, under different environmental stressors, such as temperature and solar irradiance. Measurements were performed using an infra-red gas analysis (IRGA) instrument which had a chamber allowing for precise quantification of CO₂ concentrations; additional photophysiological and biochemical responses were also measured. CO₂ assimilation, along with the productivity and biosynthesis of proteins and lipids, increased during the spring, coinciding with moderate temperatures (~14 °C) and high photosynthetically active radiation (PAR). Furthermore, the increased production of photoprotective and antioxidant compounds, including phenolic compounds, and carotenoids, along with the enhancement of non-photochemical quenching (NPQ), contribute to the effective photoacclimation strategies of L. spicata. Principal component analysis (PCA) revealed seasonal associations between productivity, reactive oxygen species (ROSs), and biochemical indicators, particularly during the spring and summer. These associations, further supported by Pearson correlation analyses, suggest a high but seasonally constrained photoacclimation capacity. In contrast, the reduced productivity and photoprotection observed in the summer suggest increased physiological vulnerability to heat and light stress. Overall, our findings position L. spicata as a promising nature-based solution for climate change mitigation. Full article

The present study systematically investigated the cesium (Cs) enrichment characteristics and physiological responses to Cs exposure in radish (Raphanus sativus L.) seedlings under hydroponic conditions through integrated physiological, biochemical, and transcriptome analyses. The results showed that the Cs content in radish roots, stems, and cotyledons increased progressively with rising Cs concentrations (0.25–2 mM), and Cs mainly accumulated in the cotyledon. The transfer factor (TF) increased by 63.29% (TF = 3.87) as the Cs concentration increased from 0.25 to 2 mM, while the biological concentration factor (BCF) decreased by 72.56% (BCF = 14.87). Severe growth inhibition was observed at 2 mM Cs stress, with biomass reduction reaching 29.73%. The carotenoid content decreased by 11.92%; however, the total chlorophyll content did not change significantly, and the photosynthesis of radish was not affected. In addition, Cs exposure disrupted mineral nutrient homeostasis, decreasing potassium (K), sodium (Na), magnesium (Mg), and iron (Fe) content. The superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, reactive oxygen species (ROS), and malondialdehyde (MDA) content increased under the different Cs treatments, which indicated that Cs exposure induced oxidative stress response in radish seedlings. Transcriptome analysis detected a total of 4326 differentially expressed genes (DEGs), in which altered expression patterns in genes associated with mineral transport, antioxidant systems, and carotenoid biosynthesis pathways in radish under 2 mM Cs treatment were observed. In conclusion, this study comprehensively investigated the physiological and molecular responses of radish to Cs stress, revealing that Cs accumulation exhibited site-specific preference and concentration dependence and induced physiological disturbances, including growth inhibition and photosynthetic pigment metabolism alterations. At the transcription level, Cs activated the enzymatic antioxidant system, related genes, and stress-response pathways. Notably, this study is the first to demonstrate that Cs disrupts plant mineral nutrition homeostasis and inhibits carotenoid biosynthesis. These findings establish a crucial theoretical foundation for utilizing radish in Cs-contaminated phytoremediation strategies. Full article

Background: Natural astaxanthin, a commercially valuable carotenoid, is primarily sourced from Haematococcus pluvialis, a microalga known for its remarkable resilience to environmental stress. Methods: In this study, the physiological and transcriptomic responses of H. pluvialis to ND were investigated at various time points under high light conditions. Results: Under high light conditions, nitrogen deprivation (ND) enhances astaxanthin content (33.23 mg g⁻¹) while inhibiting the formation of the secondary cell wall (SCW), increasing astaxanthin content by 29% compared to the nitrogen-replete group (25.64 mg g⁻¹); however, the underlying mechanisms remain unclear. ND reduced chlorophyll fluorescence parameters, elevated reactive oxygen species (ROS) levels, and increased starch and total sugar accumulation while decreasing protein and lipid content. Fatty acid content increased on the first day but had declined by the fifth day. A transcriptomic analysis revealed substantial alterations in gene expression in response to ND. Genes associated with the TCA cycle, glycolysis, astaxanthin biosynthesis, and cell motility were upregulated, while those involved in photosynthesis, lipid synthesis, ribosome biogenesis, amino acid synthesis, and SCW synthesis were downregulated. Additionally, ND modulated the expression of genes involved in ROS scavenging. Conclusions: These findings provide critical insights into the adaptive mechanisms of H. pluvialis in response to ND under high light, contributing to the development of strategies for enhanced production of astaxanthin-rich motile cells. Full article

Lycopene is a natural carotenoid with antioxidation properties. The objective of the present study was to investigate the roles of glutamate and proline in lycopene biosynthesis in a newly isolated purple non-sulfur bacterium Cereibacter sphaeroides DT.1, under aerobic conditions. This strain contained a distinct CrtI₄ capable of converting phytoene to lycopene via four-step desaturation. In order to enhance lycopene production, a crtC knockout mutant was constructed via homologous recombination. Supplementation with glutamate or proline to fermentative medium significantly enhanced intracellular lycopene accumulation in wildtype strain by a respective 99.40 ± 0.54% and 101.70 ± 0.49% and in a ΔcrtC mutant strain by 38.13 ± 0.15% and 39.83 ± 0.27%, respectively. Differential transcriptomic and metabolomic analyses showed that these promoting effects were associated with downregulation of the expression of the acyclic carotenoid 1,2-hydratase gene, and increased accumulation of lycopene precursors such as pyruvate and acetyl-CoA. The fermentation conditions for lycopene production were optimized through shake flask experiments. Feasibility for lycopene production was confirmed in a fed-batch cultivation process and a high yield of 151.10 ± 0.13 mg/L was achieved. This ΔcrtC mutant strain exhibited advantages, such as relatively lower oxygen demand and no need for illumination, making it a potentially useful strain for lycopene production under aerobic conditions. Full article

For photosynthesis, oxygenic phototrophic organisms necessarily contain not only chlorophylls but also carotenoids. Various carotenoids have been identified in algae and taxonomic studies of algae have been conducted. In this review, the relationship between the distribution of chlorophylls and carotenoids and the phylogeny of sea and freshwater oxygenic phototrophs, including cyanobacteria, red algae, brown algae, and green algae, is summarized. These phototrophs contain division- or class-specific chlorophylls and carotenoids, such as fucoxanthin, peridinin, diadinoxanthin, and siphonaxanthin. The distribution of β-carotene and its derivatives, including β-carotene, zeaxanthin, violaxanthin, neoxanthin, diadinoxanthin, fucoxanthin, and peridinin (β-branch carotenoids), are limited to divisions of a part of Rhodophyta, Cryptophyta, Heterokontophyta, Haptophyta, and Dinophyta. Meanwhile, the distribution of α-carotene and its derivatives, such as lutein, loroxanthin, and siphonaxanthin (α-branch carotenoids), are limited to divisions of a part of Rhodophyta (macrophytic type), Cryptophyta, Euglenophyta, Chlorarachniophyta, and Chlorophyta. In addition, carotenogenesis pathways are also discussed based on the chemical structures of carotenoids and the known characteristics of carotenogenesis enzymes in other organisms. The specific genes and enzymes for carotenogenesis in algae are not yet known. Most carotenoids bind to membrane-bound pigment-protein complexes, such as reaction centers and light-harvesting complexes. Some carotenoids function in photosynthesis and are briefly summarized. Water-soluble peridinin-chlorophyll a-protein (PCP) and orange carotenoid protein (OCP) have also been characterized. This review is a summary and update from the previous review on the distribution of major carotenoids, primary carotenogenesis pathways, and the characteristics of carotenogenesis enzymes and genes. Full article

Chinese cabbage (Brassica rapa L. ssp. pekinensis) is an important food crop. However, its growth and development are commonly impacted by black spot disease. To examine the response mechanisms of Chinese cabbage to black spot disease, transcriptome and metabolome sequencing were performed on the leaves of Chinese cabbage genotypes J405 (resistant) and B214 (susceptible), 48 h post-infection (hpi) with Alternaria brassicicola. Expression of essential genes in the jasmonic acid, cytokinin, and auxin signaling pathways of both Chinese cabbage genotypes was inhibited. The expression of the pathogenesis-related protein 1 (PR1) gene mediated by the salicylic acid pathway is inhibited in the Chinese cabbage genotype B214. The basic endochitase B (CHIB) gene in the ethylene pathway of both Chinese cabbage genotypes was upregulated. The accumulation of reactive oxygen species in the disease spots of Chinese cabbage genotype J405 was greater than in genotype B214. The respiratory burst oxidase (RBOH) gene in the reactive oxygen species metabolic pathway was significantly upregulated in genotype J405, while no change was observed in genotype B214. We found that oxidation-reduction-related genes such as type-2 peroxiredoxin genes, NADPH-dependent thioredoxin reductase genes, glutathione peroxidase genes, and glutathione S-transfer genes were differentially expressed across both Chinese cabbage genotypes at 48 hpi. Metabolomics demonstrated that delta-tocopherol and S-hexyl glutathione were all downregulated in genotype J405, while they were upregulated in genotype B214. This approach also identified differential expression of genes in the carotenoid biosynthesis pathway, the glycinebetaine biosynthesis pathway, as well as in the specific sulfur glycoside metabolism pathway. These findings indicate that ethylene signaling is important in the hormone signaling regulatory network-mediated disease resistance and defense in Chinese cabbage. When facing pathogen infection, hormone transduction pathways associated with growth and development in Chinese cabbage are inhibited. The accumulation of reactive oxygen species and the outbreak of various secondary metabolites may endow the Chinese cabbage genotype J405 with increased resistance to black spot disease. Full article

(1) Background: Oxygen has exerted a great effect in shaping the environment and driving biological diversity in Earth’s history. Green lineage has evolved primary and secondary carotenoid biosynthetic systems to adapt to Earth’s oxygenation, e.g., Haematococcus lacustris, which accumulates the highest amount of secondary astaxanthin under stresses. The two systems are controlled by lycopene ε-cyclase (LCYE) and β-cyclase (LCYB), which leave an important trace in Earth’s oxygenation. (2) Objectives: This work intends to disclose the underlying molecular evolutionary mechanism of Earth’s oxygenation in shaping green algal carotenogensis with a special focus on lycopene cyclases. (3) Methods: The two kinds of cyclases were analyzed by site-directed mutagenesis, phylogeny, divergence time and functional divergence. (4) Results: Green lineage LCYEs appeared at ~1.5 Ga after the first significant appearance and accumulation of atmospheric oxygen, the so-called Great Oxygenation Event (GOE), from which LCYBs diverged by gene duplication. Bacterial β-bicyclases evolved from β-monocyclase. Enhanced catalytic activity accompanied evolutionary transformation from ε-/β-monocyclase to β-bicyclase. Strong positive selection occurred in green lineage LCYEs after the GOE and in algal LCYBs during the second oxidation, the Neoproterozoic Oxygenation Event (NOE). Positively selected sites in the catalytic cavities of the enzymes controlled the mono-/bicyclase activity, respectively. Carotenoid profiling revealed that oxidative adaptation has been wildly preserved in evolution. (5) Conclusions: the functionalization of the two enzymes is a result of primary to secondary adaptations to Earth’s oxygenation. Full article

Mongolian oak (Quercus mongolica) is a common building material and landscaping tree species in northern China, with significant economic and ecological value. Its seedling growth is inhibited by high light intensity, but the mechanism by which light stress affects the growth and development of its seedlings remains unclear. In this study, we investigated the phenotypes, physiological processes, and molecular responses of 3-year-old Mongolian oak seedlings under different light treatments: full light (Sck), light shading (S1; 40% light), moderate shading (S2; 20% light), and severe shading (S3; 3% light). Compared to Sck, the S1 and S2 treatments resulted in higher leaf area, photosynthetic pigment content, photosynthesis rates, soluble sugar contents, and soluble protein contents in Mongolian oak seedlings. The S1 and S2 treatments also promoted seedling height and diameter growth and resulted in lower degrees of membrane lipid peroxidation, cell membrane permeability, and antioxidant enzyme activity. In contrast, severe shading (S3) significantly inhibited seedling height and diameter growth due to the lower net photosynthetic rate, and exhibiting higher degrees of membrane lipid peroxidation and cell membrane permeability. Shading treatments (S1 and S2) alleviated the negative effects of strong light on the growth and development of Mongolian oak seedlings, with the S2 treatment having the greatest effect. However, severe shading (S3) inhibited growth and development. A total of 3726 differentially expressed genes (DEGs) were detected in leaves under different shading treatments in RNA sequencing analysis. Among these, 1691, 3150, and 824 DEGs were detected in the Sck-S1, Sck-S2, and S1-S2 comparison groups, respectively. The different shading treatments determined common expression regulation pathways, including carotenoid biosynthesis, photosynthetic antenna proteins, and mitogen activated protein kinase (MAPK) signal transduction. Shading induced increases in gene expression levels in light harvesting complexes, which are related to changes in gene expression in the photosynthetic system, leading to changes in photosynthetic physiology. The expression levels of genes related to reactive oxygen species signal perception and activation enzymes were upregulated in Sck. Together, these findings revealed the response mechanisms of Mongolian oak seedlings to different shading levels at the physiological and molecular levels, providing a scientific basis and technical support for the cultivation and large-scale production of Mongolian oak seedlings. Full article

Common vetch (Vicia sativa L.) is an important annual diploid leguminous forage. In the present study, transcriptomic profiling in common vetch in response to salt stress was conducted using a salt-tolerant line (460) and a salt-sensitive line (429). The common responses in common vetch and the specific responses associated with salt tolerance in 460 were analyzed. Several KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, including plant hormone and MAPK (mitogen-activated protein kinase) signaling, galactose metabolism, and phenylpropanoid phenylpropane biosynthesis, were enriched in both lines, though some differentially expressed genes (DEGs) showed distinct expression patterns. The roots in 460 showed higher levels of lignin than in 429. α-linolenic acid metabolism, carotenoid biosynthesis, the photosynthesis-antenna pathway, and starch and sucrose metabolism pathways were specifically enriched in salt-tolerant line 460, with higher levels of accumulated soluble sugars in the leaves. In addition, higher transcript levels of genes involved in ion homeostasis and reactive oxygen species (ROS) scavenging were observed in 460 than in 429 in response to salt stress. The transcriptomic analysis in common vetch in response to salt stress provides useful clues for further investigations on salt tolerance mechanism in the future. Full article

Drought is one of the most detrimental environmental factors restricting the growth of wheat (Triticum aestivum L.). The investigation of the impact of uniconazole on carbon metabolism in wheat seedlings under drought stress could provide new insights into wheat stress physiology and tolerance. The effects of uniconazole (30 mg L⁻¹) on wheat drought tolerance were investigated via a physiological analysis of the wheat genotypes ‘Wansu 1510’ (WS1510) and ‘Huacheng wheat 1688’ (HC1688) under a 15% polyethylene glycol (PEG) and 30% PEG treatment and a transcriptome analysis of ‘Wansu 1510’ (WS1510) under a 30% PEG treatment. The results revealed that uniconazole significantly increased the leaf relative water content (RWC), reduced plant height, and counteracted the reduction in fresh weight and root length under drought stress. It inhibited the excessive accumulation of reactive oxygen species (ROS) and protected against membrane lipid peroxidation caused by drought stress by regulating superoxide dismutase (SOD) gene expression, enhancing antioxidant enzymes activities, and adjusting the content of osmoregulatory compounds in drought-stressed plants. Furthermore, uniconazole treatment increased chlorophyll (Chl) and carotenoid (Car) contents, inhibited the increase in sucrose concentration, and alleviated the reduction in starch content due to increased sucrose synthase (SS) activity under drought stress. Transcriptome sequencing revealed that uniconazole regulated the expression of genes associated with starch and sucrose metabolism, porphyrin and chlorophyll metabolism, the photosynthetic antenna proteins, carotenoid biosynthesis, and carbon fixation in photosynthetic organisms, which are involved in carbon metabolism processes and photosynthetic pigment production and which regulate the conversion of sucrose and starch under drought stress. Our findings emphasize the importance of exogenous uniconazole in regulating carbon metabolism in wheat. Full article

Efficient induction of astaxanthin (AXT) biosynthesis remains a considerable challenge for the industrialization of the biorefinement of the microalga Haematococcus lacustris. In this study, we evaluated the technical feasibility of photosynthetic electrotreatment to enhance AXT accumulation in H. lacustris. The AXT content of H. lacustris electrotreated at an optimal current intensity (10 mA for 4 h) was 21.8% to 34.9% higher than that of the untreated control group, depending on the physiological state of the initial palmella cells. The contents of other carotenoids (i.e., canthaxanthin, zeaxanthin, and β-carotene) were also increased by this electrotreatment. However, when H. lacustris cells were exposed to more intense electric treatments, particularly at 20 and 30 mA, cell viability significantly decreased to 84.2% and 65.6%, respectively, with a concurrent reduction in the contents of both AXT and the three other carotenoids compared to those of the control group. The cumulative effect of electric stimulation is likely related to two opposing functions of reactive oxygen species, which facilitate AXT biosynthesis as signaling molecules while also causing cellular damage as oxidizing radicals. Collectively, our findings indicate that when adequately controlled, electric stimulation can be an effective and eco-friendly strategy for inducing targeted carotenoid pigments in photosynthetic microalgae. Full article

The role of melatonin in plant growth and response to environmental stress has been widely demonstrated. However, the physiological and molecular regulation of salt tolerance in wheat seedlings by melatonin remains unclear. In this study, we investigated changes in phenotype, physiology, photosynthetic parameters, and transcript levels in wheat seedlings to reveal the role of melatonin in the regulation of salt tolerance in wheat. The results indicate that the application of exogenous melatonin significantly alleviates growth inhibition, reactive oxygen species accumulation, and membrane oxidative damage induced by salt stress in wheat. Additionally, exogenous melatonin increased antioxidant enzyme activity and regulated photosynthetic gas exchange. Transcriptomic data showed a significant up-regulation of genes encoding light-harvesting chlorophyll protein complex proteins in photosynthesis and genes related to chlorophyll and carotenoid biosynthesis under the influence of melatonin. These results suggest that exogenous melatonin improves salt tolerance in wheat seedlings by enhancing the antioxidant, photoprotective, and photosynthesis activities. Full article

Plants are exposed to a variety of abiotic and biotic stresses leading to increased formation of reactive oxygen species (ROS) in plant cells. ROS are capable of oxidizing proteins, pigments, lipids, nucleic acids, and other cell molecules, disrupting their functional activity. During the process of evolution, numerous antioxidant systems were formed in plants, including antioxidant enzymes and low molecular weight non-enzymatic antioxidants. Antioxidant systems perform neutralization of ROS and therefore prevent oxidative damage of cell components. In the present review, we focus on the biosynthesis of non-enzymatic antioxidants in higher plants cells such as ascorbic acid (vitamin C), glutathione, flavonoids, isoprenoids, carotenoids, tocopherol (vitamin E), ubiquinone, and plastoquinone. Their functioning and their reactivity with respect to individual ROS will be described. This review is also devoted to the modern genetic engineering methods, which are widely used to change the quantitative and qualitative content of the non-enzymatic antioxidants in cultivated plants. These methods allow various plant lines with given properties to be obtained in a rather short time. The most successful approaches for plant transgenesis and plant genome editing for the enhancement of biosynthesis and the content of these antioxidants are discussed. Full article

In purple bacteria, the genes of the carotenoid pathways are part of photosynthesis gene clusters which were distributed among different species by horizontal gene transfer. Their close organisation facilitated the first-time cloning of carotenogenic genes and promoted the molecular investigation of spheroidene and spirilloxanthin biosynthesis. This review highlights the cloning of the spheroidene and spirilloxanthin pathway genes and presents the current knowledge on the enzymes involved in the carotenoid biosynthesis of purple sulphur and non-sulphur bacteria. Mostly, spheroidene or spirilloxanthin biosynthesis exists in purple non-sulphur bacteria but both pathways operate simultaneously in Rubrivivax gelatinosus. In the following years, genes from other bacteria including purple sulphur bacteria with an okenone pathway were cloned. The individual steps were investigated by kinetic studies with heterologously expressed pathway genes which supported the establishment of the reaction mechanisms. In particular, the substrate and product specificities revealed the sequential order of the speroidene and spiriloxanthin pathways as well as their interactions. Information on the enzymes involved revealed that the phytoene desaturase determines the type of pathway by the formation of different products. By selection of mutants with amino acid exchanges in the putative substrate-binding site, the neurosporene-forming phytoene desaturase could be changed into a lycopene-producing enzyme and vice versa. Concerning the oxygen groups in neurosporene and lycopene, the tertiary alcohol group at C1 is formed from water and not by oxygenation, and the C2 or C4 keto groups are inserted differently by an oxygen-dependent or oxygen-independent ketolation reaction, respectively. Full article

Staphylococcus aureus membranes contain carotenoids formed during the biosynthesis of staphyloxanthin. These carotenoids are considered virulence factors due to their activity as scavengers of reactive oxygen species and as inhibitors of antimicrobial peptides. Here, we show that the growth of S. aureus under oxygen-restricting conditions downregulates carotenoid biosynthesis and modifies phospholipid content in biofilms and planktonic cells analyzed using LC-MS. At oxygen-restrictive levels, the staphyloxanthin precursor 4,4-diapophytofluene accumulates, indicating that the dehydrogenation reaction catalyzed by 4,4′-diapophytoene desaturases (CrtN) is inhibited. An increase in lysyl-phosphatidylglycerol is observed under oxygen-restrictive conditions in planktonic cells, and high levels of cardiolipin are detected in biofilms compared to planktonic cells. Under oxygen-restriction conditions, the biophysical parameters of S. aureus membranes show an increase in lipid headgroup spacing, as measured with Laurdan GP, and decreased bilayer core order, as measured with DPH anisotropy. An increase in the liquid–crystalline to gel phase melting temperature, as measured with FTIR, is also observed. S. aureus membranes are therefore less condensed under oxygen-restriction conditions at 37 °C. However, the lack of carotenoids leads to a highly ordered gel phase at low temperatures, around 15 °C. Carotenoids are therefore likely to be low in S. aureus found in tissues with low oxygen levels, such as abscesses, leading to altered membrane biophysical properties. Full article