Morpho-functionality of Carbon Metabolism in Seaweeds

Engineered Nanomaterial Exposure Affects Organelle Genetic Material Replication in Arabidopsis thaliana

Mitochondria and chloroplasts not only are cellular energy sources but also have important regulatory and developmental roles in cell function. CeO₂, FeOx ENMs, ZnS, CdS QDs, and relative metal salts were utilized in Murashige-Skoog (MS) synthetic growth medium at different concentrations (80-500 mg L^-1) and times of exposures (0-20 days). Analysis of physiological and molecular response of A. thaliana chloroplasts and mitochondrion demonstrates that ENMs increase or decrease functionality and organelle genome replication. Exposure to nanoscale CeO₂ and FeOx causes an 81-105% increase in biomass, whereas ZnS and CdS QDs yielded neutral or a 59% decrease in growth, respectively. Differential effects between ENMs and their corresponding metal salts highlight nanoscale-specific response pathways, which include energy production and oxidative stress response. Differences may be ascribed to ENM and the metal salt dissolution rate and the toxicity of the metal ion, which suggests eventual biotransformation processes occurring within the plant. With regard to specific effects on plastid (pt) and mitochondrial (mt) DNA, CdS QD exposure triggered potential variations at the substoichiometric level in the two organellar genomes, while nanoscale FeOx and ZnS QDs caused a 1- to 3-fold increase in ptDNA and mtDNA copy numbers. Nanoparticle CeO₂ exposure did not affect ptDNA and mtDNA stoichiometry. These findings suggest that modification in stoichiometry is a potential morpho-functional adaptive response to ENM exposure, triggered by modifications of bioenergetic redox balance, which leads to reducing the photosynthesis or cellular respiration rate.

Rate and fate of dissolved organic carbon release by seaweeds: A missing link in the coastal ocean carbon cycle

Dissolved organic carbon (DOC) release by seaweeds (marine macroalgae) is a critical component of the coastal ocean biogeochemical carbon cycle but is an aspect of seaweed carbon physiology that we know relatively little about. Seaweed-derived DOC is found throughout coastal ecosystems and supports multiple food web linkages. Here, we discuss the mechanisms of DOC release by seaweeds and group them into passive (leakage, requires no energy) and active release (exudation, requires energy) with particular focus on the photosynthetic "overflow" hypothesis. The release of DOC from seaweeds was first studied in the 1960s, but subsequent studies use a range of units hindering evaluation: we convert published values to a common unit (μmol C · g DW^-1 · h^-1 ) allowing comparisons between seaweed phyla, functional groups, biogeographic region, and an assessment of the environmental regulation of DOC production. The range of DOC release rates by seaweeds from each phylum under ambient environmental conditions was 0-266.44 μmol C · g DW^-1 · h^-1 (Chlorophyta), 0-89.92 μmol C · g DW^-1 · h^-1 (Ochrophyta), and 0-41.28 μmol C · g DW^-1 · h^-1 (Rhodophyta). DOC release rates increased under environmental factors such as desiccation, high irradiance, non-optimal temperatures, altered salinity, and elevated dissolved carbon dioxide (CO₂ ) concentrations. Importantly, DOC release was highest by seaweeds that were desiccated (<90 times greater DOC release compared to ambient). We discuss the impact of future ocean scenarios (ocean acidification, seawater warming, altered irradiance) on DOC release rates by seaweeds, the role of seaweed-derived DOC in carbon sequestration models, and how they inform future research directions.

Seaweed Proteins as a Source of Bioactive Peptides

Seaweeds have received great attention as a vegetarian and sustainable marine source of protein, which does not need irrigation, arable land, and fertilization. Besides, seaweeds are considered as an untapped resource for discovering bioactive compounds with health benefits where bioactive peptides have shown outstanding potential. This review provides a detailed overview of available scientific knowledge on production methods, bioactivity and application of peptides from seaweed proteins. The emphasis is on the effects from seaweed varieties and peptide production conditions on the bioactivity of the peptides and their potential health benefits. Bioactive properties of seaweed peptides, including antioxidant, antihypertensive, antidiabetic, anti-inflammatory, anticancer activities and other potential health benefits, have been discussed. It also covers current challenges and required future research and innovations for the successful application of seaweeds proteins as a sustainable source of bioactive peptides. Effects from seasonal variation of seaweed composition on the bioactivity of their peptides, difficulties in the extraction of proteins from seaweed complex structure, scalability and reproducibility of the developed methods for the production of bioactive peptides, the safety of the peptides are examples of highlighted challenges. Further studies on the bioavailability of the seaweed bioactive peptides and validation of the results in animal models and human trials are needed before their application as functional foods or pharmaceutical ingredients.

Comparative Transcriptome Analysis Reveals Candidate Genes Related to Structural and Storage Carbohydrate Biosynthesis in Kelp Saccharina japonica (Laminariales, Phaeophyceae)

Saccharina japonica is a brown macroalga that has been commercially cultivated in China for almost a century. As a natural raw material, it is widely used in the food and pharmaceutical industries, and it may potentially be useful for biofuel production. However, little is known about the genes involved in carbohydrate biosynthesis, and their regulation is less understood. In this study, the analysis of growth traits and alginate and mannitol contents suggested that sporophyte development could be divided into four stages. Accordingly, we performed transcriptome analysis of the S. japonica sporophyte. In total, 589 million clean reads were generated, and 4,514 novel genes were identified. Gene expression analysis revealed that 2,542 genes were differentially expressed. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis indicated that these genes were significantly enriched in "Carbon metabolism," "Photosynthesis," and "Photosynthesis-antenna proteins" pathways, which are important for metabolism of various carbohydrates during sporophyte development. Systematic analysis identified the genes encoding enzymes for the biosynthesis of cell wall carbohydrates (including alginate, fucoidan, and cellulose) and cytoplasm storage carbohydrates (mannitol, laminarin, and trehalose). Among them, some key genes associated with carbohydrate content were further identified based on detailed expression profiling, representing good candidates for further functional studies. This study provides a global view of the carbohydrate metabolism process and an important resource for functional genomics studies in S. japonica. The results obtained lay the basis for elucidating the molecular mechanism of carbohydrate biosynthesis and for genetic breeding of carbohydrates-related traits in kelp.

Heat stress responses and population genetics of the kelp Laminaria digitata (Phaeophyceae) across latitudes reveal differentiation among North Atlantic populations

To understand the thermal plasticity of a coastal foundation species across its latitudinal distribution, we assess physiological responses to high temperature stress in the kelp Laminaria digitata in combination with population genetic characteristics and relate heat resilience to genetic features and phylogeography. We hypothesize that populations from Arctic and cold-temperate locations are less heat resilient than populations from warm distributional edges. Using meristems of natural L. digitata populations from six locations ranging between Kongsfjorden, Spitsbergen (79°N), and Quiberon, France (47°N), we performed a common-garden heat stress experiment applying 15°C to 23°C over eight days. We assessed growth, photosynthetic quantum yield, carbon and nitrogen storage, and xanthophyll pigment contents as response traits. Population connectivity and genetic diversity were analyzed with microsatellite markers. Results from the heat stress experiment suggest that the upper temperature limit of L. digitata is nearly identical across its distribution range, but subtle differences in growth and stress responses were revealed for three populations from the species' ecological range margins. Two populations at the species' warm distribution limit showed higher temperature tolerance compared to other populations in growth at 19°C and recovery from 21°C (Quiberon, France), and photosynthetic quantum yield and xanthophyll pigment responses at 23°C (Helgoland, Germany). In L. digitata from the northernmost population (Spitsbergen, Norway), quantum yield indicated the highest heat sensitivity. Microsatellite genotyping revealed all sampled populations to be genetically distinct, with a strong hierarchical structure between southern and northern clades. Genetic diversity was lowest in the isolated population of the North Sea island of Helgoland and highest in Roscoff in the English Channel. All together, these results support the hypothesis of moderate local differentiation across L. digitata's European distribution, whereas effects are likely too weak to ameliorate the species' capacity to withstand ocean warming and marine heatwaves at the southern range edge.

Interaction of Photoprotective and Acclimation Mechanisms in Ulva rigida (Chlorophyta) in Response to Diurnal Changes in Solar Radiation in Southern Chile

Species of the genus Ulva (Chlorophyta) are regarded as opportunistic organisms, which efficiently adjust their metabolism to the prevailing environmental conditions. In this study, changes in chlorophyll-a fluorescence-based photoinhibition of photosynthesis, electron transport rates, photosynthetic pigments, lipid peroxidation, total phenolic compounds, and antioxidant metabolism were investigated during a diurnal cycle of natural solar radiation in summer (for 12 h) under two treatments: photosynthetically active radiation (PAR: 400-700 nm) and PAR+ ultraviolet (UV) radiation (280-700 nm). In the presence of PAR alone, Ulva rigida showed dynamic photoinhibition, and photosynthetic parameters and pigment concentrations decreased with the intensification of the radiation. On the other hand, under PAR+UV conditions a substantial decline up to 43% was detected and an incomplete fluorescence recovery, also, P-I curve values remained low in relation to the initial condition. The phenolic compounds increased their concentration only in UV radiation treatments without showing a correlation with the antioxidant activity. The enzimatic activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased over 2-fold respect at initial values during the onset of light intensity. In contrast, catalase (CAT) increased its activity rapidly in response to the radiation stress to reach maxima at 10 a.m. and decreasing during solar. The present study suggests that U. rigida is capable of acclimating to natural radiation stress relies on a concerted action of various physiological mechanisms that act at different times of the day and under different levels of environmental stress.

Distribution of natural ingredients suggests a complex network of metabolic transport between source and sink tissues in the brown alga Fucus vesiculosus

MAIN CONCLUSION

Tight regulation of intra-thallus metabolite distribution in Fucus vesiculosus in late summer reveals the complex biochemical processes complying with reproduction and the preparation to the dark season. We used inductively coupled plasma atomic emission spectroscopy to study the tissue-specific elemental composition, and gas chromatography coupled to mass spectrometry to study the distribution of small-molecular weight primary and secondary metabolites of the brown alga Fucus vesiculosus thalli in the reproductive phase. Beyond general physiological requirements, the observed distribution of the analysed nutrients was also found to depend on characteristics related to the season of harvesting, i.e., the reproductive period. However, a particular curious result was the high metabolic activity found in the stipe of the plant. In conclusion, our data not only provide valuable information for industrial use of fucoids targeting specific algal ingredients, but also give highly interesting insights in the multifaceted system of intra-thallus biochemical interactions during reproduction of the brown algae.

Physiological acclimation of Lessonia spicata to diurnal changing PAR and UV radiation: differential regulation among down-regulation of photochemistry, ROS scavenging activity and phlorotannins as major photoprotective mechanisms

Intertidal macroalgae are constantly subjected to high variations in the quality and quantity of incident irradiance that can eventually generate detrimental effect on the photosynthetic apparatus. The success of these organisms to colonize the stressful coastal habitat is mainly associated with the complexity of their morphological structures and the efficiency of the anti-stress mechanisms to minimize the physiological stress. Lessonia spicata (Phaeophyceae), a brown macroalga, that inhabits the intertidal zone in central-southern Chile was studied in regard to their physiological (quantum yield, electron transport rate, pigments) and biochemical (phlorotannins content, antioxidant metabolism, oxidative stress) responses during a daily light cycle under natural solar radiation. Major findings were that F v/F m, photosynthetic parameters (ETRmax, alpha, E k) and pigments in L. spicata showed an inverse relationship to the diurnal changes in solar radiation. Phlorotannins levels and antioxidant activity showed their highest values in treatment that included UV radiation. There was an increase in SOD and APX in relation at light stress, with a peak in activity between 5.2 and 10.1 W m-2 of biologically effective dose. The increase in peroxidative damage was proportional to light dose. These results indicated that different light doses can trigger a series of complementary mechanisms of acclimation in L. spicata based on: (i) down-regulation of photochemistry activity and decrease in concentration of photosynthetic pigments; (ii) induction of phenolic compounds with specific UV-screening functions; and (iii) reactive oxygen species (ROS) scavenging activity via complementary repair of the oxidative damage through increased activity of antioxidant enzymes and potentially increased amounts of phenolic compounds.

Restructuring of Epibacterial Communities on Fucus vesiculosus forma mytili in Response to Elevated pCO2 and Increased Temperature Levels

Marine multicellular organisms in composition with their associated microbiota-representing metaorganisms-are confronted with constantly changing environmental conditions. In 2110, the seawater temperature is predicted to be increased by ~5°C, and the atmospheric carbon dioxide partial pressure (pCO2) is expected to reach approximately 1000 ppm. In order to assess the response of marine metaorganisms to global changes, e.g., by effects on host-microbe interactions, we evaluated the response of epibacterial communities associated with Fucus vesiculosus forma mytili (F. mytili) to future climate conditions. During an 11-week lasting mesocosm experiment on the island of Sylt (Germany) in spring 2014, North Sea F. mytili individuals were exposed to elevated pCO2 (1000 ppm) and increased temperature levels (Δ+5°C). Both abiotic factors were tested for single and combined effects on the epibacterial community composition over time, with three replicates per treatment. The respective community structures of bacterial consortia associated to the surface of F. mytili were analyzed by Illumina MiSeq 16S rDNA amplicon sequencing after 0, 4, 8, and 11 weeks of treatment (in total 96 samples). The results demonstrated that the epibacterial community structure was strongly affected by temperature, but only weakly by elevated pCO2. No interaction effect of both factors was observed in the combined treatment. We identified several indicator operational taxonomic units (iOTUs) that were strongly influenced by the respective experimental factors. An OTU association network analysis revealed that relationships between OTUs were mainly governed by habitat. Overall, this study contributes to a better understanding of how epibacterial communities associated with F. mytili may adapt to future changes in seawater acidity and temperature, ultimately with potential consequences for host-microbe interactions.