Selaginella martensii is a living member of lycophytes, an early divergent group of vascular plants. This shade-adapted species can acclimate to various light regimes, from deep shade to high light, with a gain in carboxylation capacity accompanied by modulations in thylakoid composition, including increased relative amount of photosystem I (PSI) compared to photosystem II (PSII). It was hypothesized that, as in angiosperms, the photosynthetic acclimation of S. martensii to high light may lead to increased cyclic electron flow around PSI (CEF), with changes in excitation distribution between PSI and PSII and with modulations of electron carrier pools. After long-term acclimation to deep shade (LL), intermediate shade (ML) and high light (HL) regimes, plants were compared using chlorophyll a fluorescence, P700 oxidation, electrochromic bandshift, and transmission electron microscopy of the thylakoid system. As expected, a 75% increase in CEF occurred from LL to HL plants, facilitated by a preferential energy distribution to PSI. However, some unique characteristics distinguish S. martensii from common models of long-term thylakoid photoregulation. The pools of electron transporters did not increase linearly with the electron fluxes from LL to HL plants; rather, the enhancement of electron transport depended on unique combinations of capacity and mobility of the electron carriers, the latter determined by the extent of thylakoid shrinkage. Moreover, especially in shade-acclimated plants, the fraction of oxidized PSI exceeded that of reduced QA, therefore keeping PSI under a persistent shortage of electrons already at low light intensities.

Coccolitophores, such as Gephyrocapsa huxleyi, can have multiple interesting biotechnological applications thanks to their ability to produce complex structures made of CaCO3, called coccolith, and a biomass rich in valuable molecules. Unfortunately, they usually reach low cellular density in standard conditions, hindering actual industrial applications. To enhance growth, CaCO3 may be used instead of standard CaCl2. Here, shell-derived CaCO3 was also tested to valorise oyster shells, which are not recyclable and can cause environmental harm if not disposed of correctly. G. huxleyi cultures were grown in f/2 medium prepared using standard artificial seawater, artificial seawater with pure CaCO3 in place of CaCl2, and artificial seawater with the pulverised shells of Magallana gigas (Pacific oyster) instead of CaCl2. Cultures were monitored for 14 days, and final dry biomass concentration, photosynthetic pigment and total protein concentrations were evaluated. Moreover, coccolith morphology was checked through scanning electron microscopy. Replacing CaCl2 with pure CaCO3 increased cell density roughly sixfold relative to the control; using pulverised oyster shells yielded the greatest effect, with cell densities about 26 times higher than CaCl2. Cells grown in the medium added with pulverised oyster shells were smaller, exhibited higher pigment content per dry weight and a protein content comparable with the control. The bulk composition of the oyster shell revealed the presence of trace elements, like Mn, Fe and Cu, that could have enhanced the algal growth. Results indicate pulverised oyster shells can be a sustainable and effective calcium source to valorise waste and enhance G. huxleyi biomass production.

Microalgae are versatile microorganisms that produce bioactive compounds with antioxidant, anti-inflammatory, and antimicrobial properties. Neochloris oleoabundans stands out for its adaptability and promising potential in a wide range of biotechnological applications, including the synthesis of high-value metabolites. Among the bioactive molecules of interest, extracellular vesicles (EVs) are gaining increasing attention for their potential in drug delivery and the development of novel therapeutic and healthcare products. The aim of this study is to investigate the microalga and how different growth phases can influence the yield of biologically active molecules with biotechnological relevance. For this reason N. oleoabundans (UTEX 1185) was cultivated for an unusually long period of 60 days. Measurements of the PSII maximum quantum yield indicated that the cultures remained in a healthy state even after prolonged cultivation, confirming the robustness of this strain. Biochemical characterisation of both the microalgal biomass and the conditioned medium was performed after 28 and 60 days of cultivation (corresponding to early and late stationary phases, respectively). The results suggest an enhanced production of high-value bioactive compounds during the early stationary phase, which is particularly advantageous given the higher biomass concentration at this stage. EVs were detected in the conditioned medium, with a higher abundance observed after 28 days. Transmission electron microscopy also revealed the presence of vesicles inside the cells, specifically located between the plasma membrane and the cell wall.

In this work, we combined microalgae's sorptive properties with titania-based nanoparticles' photocatalytic capabilities to develop technologies applicable to wastewater treatment while also providing valuable insights into the innovation of adsorption technologies. The coupling of Neochloris oleoabundans biomass with an inorganic nanophase enables the formation of hybrid materials integrating heavy metal adsorption with photocatalytic action. To prepare the samples, we employed a water-based colloidal method followed by a spray freeze granulation treatment. The preparation process was followed by comprehensive physicochemical characterization from the wet precursors to the final hybrid granules. Key performance indicators, including adsorption and photocatalytic activity, were assessed using two model contaminants: copper ions (for heavy metal adsorption) and Rhodamine B (for photocatalysis). The results revealed a synergistic effect of the hybrid nanomaterials, significantly enhancing the Cu2+ adsorption capacity of the biomass, which increases from 30 mg g-1 to 250 mg g-1 when coupled with the inorganic phase and is likely due to the supporting and dispersing role of the inorganic nanoparticles on the biomass. The adsorption experimental values followed the Freundlich isothermal model and pseudo-second-order kinetic model, indicating that the adsorption occurred primarily through a multimolecular layer adsorption process, consistent with chemisorption mechanisms. The photocatalytic performance of the inorganic counterpart was preserved when coupled with the microalgae, with TiO2-SiO2/biomass achieving complete Rhodamine B degradation within 1 hour.

Microalgae are gaining increasing attention for wastewater (WW) depuration thanks to their ability to remove pollutants from WW. As environmental conditions change widely geographically and throughout the year, also reaching growth-limiting temperatures during the cold season, sites and seasons specific tests are needed to assess the actual implementation of microalgae phytoremediation. In this paper, two site-specific prototype-scale experiments were performed to test the ability of an autochthonous microalga to depurate urban WW efficiently during winter. Two setups were tested: one indoor and one outdoor. We evaluated dry biomass production, photosynthetic stress, and nitrogen (N) and phosphorus (P) removals from WW. In addition, Escherichia coli concentration was monitored on the effluent. Despite the limited growth in both conditions, N was largely removed from the medium, with the highest result recorded outdoors (almost 70%). No P removal was recorded, although P content in biomass increased both indoors and outdoors, meaning that multiple processes could occur at the same time. Moreover, a huge decrease in E. coli content was recorded in both conditions, suggesting potential for effluent disinfection.

Microalgae of the Microchloropsis genus accumulate lipids and are studied for exploitation in the food/feed sector. Aquaculture, including mollusc farming, represents a fast-growing field that uses microalgae as live feed. Since microalgal cultivation and aquaculture are water-consuming, in molluscs' indoor rearing plants the re-use of water effluents is a need. In this perspective, Microchloropsis salina was chosen to test the feasibility of reusing the water recirculating in an indoor bivalve hatchery. M. salina was cultivated in static conditions in hatchery wastewater (HW) and in control synthetic media. During algal cultivation, growth, photosynthetic parameters, morphology, protein and lipid contents were evaluated. The fatty acid profile was also analysed. Besides the finding that growth kinetics and productivity were comparable, a lower efficiency in photosynthetic electron flow, accompanied by a different pigment content, characterized M. salina algae cultivated in HW. In parallel, treated algae accumulated large lipid globules and produced acidic exo-mucopolysaccharides. Lipid and fatty acids analyses highlighted interesting differences between control and treated algae, with higher lipid content, similar saturated fatty acid and monounsaturated fatty acid, but lower polyunsaturated fatty acid in HW-treated algae. Feeding tests performed on Manila clam indicated a good degree of acceptability of the alga deriving from both culturing condition.

Main conclusion A structural re-modeling of the thylakoid system, including granum size and regularity, occurs in chlorophyll-deficient wheat mutants affected by photosynthetic membrane over-reduction. Abstract In the chloroplast of land plants, the thylakoid system is defined by appressed grana stacks and unstacked stroma lamellae. This study focuses on the variations of the grana organization occurring in outdoor-grown wheat mutants characterized by low chlorophyll content and a tendency for photosynthetic membrane over-reduction. Triticum aestivum ANK-32A and Triticum durum ANDW-7B were compared to their corresponding WT lines, NS67 and LD222, respectively. Electron micrographs of chloroplasts were used to calculate grana ultrastructural parameters. Photosynthetic parameters were obtained by modulated chlorophyll fluorescence and applying Light Curves (LC) and Rapid Light Curves (RLC) protocols. For each photosynthetic parameter, the difference Δ(RLC–LC) was calculated to evaluate the flexible response to light in the examined lines. In the mutants, fewer and smaller disks formed grana stacks characterized by a marked increase in lateral and cross-sectional irregularity, both negatively correlated with the number of layers per granum. A relationship was found between membrane over-reduction and granum structural irregularity. The possible acclimative significance of a greater proportion of stroma-exposed grana domains in relieving the excess electron pressure on PSI is discussed.

The global population increase during the last century has significantly amplified freshwater demand, leading to higher wastewater (WW) production. European regulations necessitate treating WW before environmental. Microalgae have gained attention for wastewater treatment (WWT) due to their efficiency in remediating nutrients and pollutants, alongside producing valuable biomass. This study investigates the phycoremediation potential of a Chlorella-like strain isolated from urban WW in a 600L-scale system under winter conditions. Experiments in December 2021 and February 2022 tested the strain’s adaptability to varying environmental conditions, particularly temperatures (min-max temperature range: from −3.69 to 10.61 °C in December and −3.96 to 17.61 °C in February), and its ability to meet legal discharge limits. In December, low temperatures algal growth. Nitrates showed an RE of about 92%, while ammonia slightly decreased (RE, about 32%), and phosphorous remained unchanged. In February, mild temperatures increased algal density (33.3 × 106 cell mL−1) and, at the end of experiment, all nutrients were below legal limits with very high RE % (NH4+, 91.43; PO43− 97.32). Both trials showed an E. coli RE, % = 99%. The study highlights the potential of microalgae for WWT and the importance of considering seasonal variations when implementing these systems.

BACKGROUND:Microbial biofertilizers and algae-based biostimulants have been recognized for supporting sustainable agriculture. Field experiments were conducted in 2022 and 2023 growing seasons in an organic farm located in Ferrara (Italy) with the aim of evaluating plant growth-promoting microorganisms (PGPMs) and algae-based biostimulants (Biost) in tomato (Solanum lycopersicum L.). The experimental treatments were: (i) two microbial biofertilizers (PGPM_1, PGPM_2) and no inoculated plants (No_PGPM); and (ii) two algae-based biostimulant rates (0.5% (Biost_0.5%), 1.0% (Biost_1.0%)) and no application (No_Biost). PGPMs were applied at transplanting, while biostimulants at 15 and 30 days after transplanting. Treatments were replicated three times according to a split-plot experimental design. Plant characteristics were evaluated at 30 days after transplanting in No_Biost treatments. During tomato cultivation, soil plant analysis development (SPAD), nitrogen difference vegetation index (NDVI), leaf area index (LAI) and photosynthetic photon flux density (PPFD) were monitored. Tomato yield was determined. RESULTS:PGPM_2 showed the highest shoot biomass (132.9 g plant-1), plant height (44.7 cm), leaf number (34.0 plant-1) and root biomass (9.22 g plant-1). Intermediate values were observed in PGPM_1, while all parameters were lower in No_PGPM. Both PGPMs achieved higher values of SPAD, NDVI, PPFD and LAI than No_PGPM. Biost_1.0% increased all measured growth parameters followed by Biost_0.5% and No_Biost, respectively. Tomato yield was the highest for PGPM_2-Biost_1.0% (67.2 t ha-1). PGPMs affected fruit size and sugar content, while biostimulants were associated with color and lycopene. CONCLUSION:The application of microbial biofertilizers and algae-based biostimulants could be part of environment-friendly practice in organic farming. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Microalgae are considered promising sustainable sources of natural bioactive compounds to be used in biotechnological sectors. In recent years, attention is increasingly given to the search of microalgae-derived compounds with antioxidant and anti-inflammatory properties for nutraceutical or pharmacological issues. In this context, attention is usually focused on the composition and bioactivity of algae or their extracts, while less interest is driven to their biological features, for example, those related to morphology and cultivation conditions. In addition, specific studies on the antioxidant and anti-inflammatory properties of microalgae mainly concern Chlorella or Spirulina. The present work was focused on the characterization of the Chlorophyta Neochloris oleoabundans under two combinations of cultivation modes: autotrophy and glucose-induced mixotrophy, each followed by starvation. Biomass for morphological and biochemical characterization, as well as for extract preparation, was harvested at the end of each cultivation phase. Analyses indicated a different content of the most important classes of bioactive compounds with antioxidant/anti-inflammatory properties (lipids, exo-polysaccharides, pigments, total phenolics, and proteins). In particular, the most promising condition able to prompt the production of antioxidant algal biomass with anti-inflammatory properties was the mixotrophic one. Under mixotrophy, beside an elevated algal biomass production, a strong photosynthetic metabolism with high appression of thylakoid membranes and characteristics of high photo-protection from oxidative damage was observed and linked to the overproduction of exo-polysaccharides and lipids rather than pigments. Overall, mixotrophy appears a good choice to produce natural bioactive extracts, potentially well tolerated by human metabolism and environmentally sustainable.

The release of inadequately treated urban wastewater is the main cause of environmental pollution of aquatic ecosystems. Among efficient and environmentally friendly technologies to improve the remediation process, those based on microalgae represent an attractive alternative due to the potential of microalgae to remove nitrogen (N) and phosphorus (P) from wastewaters. In this work, microalgae were isolated from the centrate stream of an urban wastewater treatment plant and a native Chlorella-like species was selected for studies on nutrient removal from centrate streams. Comparative experiments were set up using 100% centrate and BG11 synthetic medium, modified with the same N and P as the effluent. Since microalgal growth in 100% effluent was inhibited, cultivation of microalgae was performed by mixing tap-freshwater with centrate at increasing percentages (50%, 60%, 70%, and 80%). While algal biomass and nutrient removal was little affected by the differently diluted effluent, morpho-physiological parameters (FV/FM ratio, carotenoids, chloroplast ultrastructure) showed that cell stress increased with increasing amounts of centrate. However, the production of an algal biomass enriched in carotenoids and P, together with N and P abatement in the effluent, supports promising microalgae applications that combine centrate remediation with the production of compounds of biotechnological interest; for example, for organic agriculture.

In vascular plants, the thylakoid architecture is dominated by the highly structured multiple membrane layers known as grana. The structural diversity of the thylakoid system among plant species is mainly determined by the adaptation to the growth light regime, according to a paradigm stating that shade-tolerant species are featured by a high membrane extension with an enhanced number of thylakoid layers per granum. In this study, the thylakoid system was analysed in Selaginella martensii Spring, a shade-adapted rainforest species belonging to lycophytes, a diminutive plant lineage, sister clade of all other vascular plants (euphyllophytes, including ferns and seed plants). The species is characterized by giant cup-shaped chloroplasts in the upper epidermis and, quantitatively less important, disk-shaped chloroplasts in the mesophyll and lower epidermis. The study aimed at the quantitative assessment of the thylakoid appression exploiting a combination of complementary methods, including electron microscopy, selective thylakoid solubilisation, electron paramagnetic resonance, and simultaneous analysis of fast chlorophyll a fluorescence and P700 redox state. With a chlorophyll a/b ratio of 2.6 and PSI/PSII ratio of 0.31, the plant confirmed two typical hallmarks of shade-adaptation. The morphometric analysis of electron micrographs revealed a 33% fraction of non-appressed thylakoid domains. However, contrasting with the structural paradigm of thylakoid shade-adaptation in angiosperms, S. martensii privileges the increase in the granum diameter in place of the increase in the number of layers building the granum. The very wide grana diameter, 727 nm on average, largely overcame the threshold of 500 nm currently hypothesized to allow an effective diffusion of long-range electron carriers. The fraction of non-appressed membranes based on the selective solubilisation of thylakoids with digitonin was 26%, lower than the morphometric determination, indicating the presence of non-appressed domains inaccessible to the detergent, most probably because of the high three-dimensional complexity of the thylakoid system in S. martensii. Particularly, strong irregularity of grana stacks is determined by assembling thylakoid layers of variable width that tend to slide apart from each other as the number of stacked layers increases.

Within the ancient vascular plant lineage known as lycophytes, many Selaginella species contain only one giant chloroplast in the upper epidermal cells of the leaf. In deep-shade species, such as S. martensii, the chloroplast is cup-shaped and the thylakoid system differentiates into an upper lamellar region and a lower granal region (bizonoplast). In this report, we describe the ultrastructural changes occurring in the giant chloroplast hosted in the epidermal cells of S. martensii during the daily relocation of the organelle. The process occurs in up to ca. 40% of the microphylls without the plants being exposed to high-light flecks. The relocated chloroplast loses its cup shape: first, it flattens laterally toward the radial cell wall and then assumes a more globular shape. The loss of the conical cell shape, the side-by-side lateral positioning of vacuole and chloroplast, and the extensive rearrangement of the thylakoid system to only granal cooperate in limiting light absorption. While the cup-shaped chloroplast emphasizes the light-harvesting capacity in the morning, the relocated chloroplast is suggested to support the renewal of the thylakoid system during the afternoon, including the recovery of photosystem II (PSII) from photoinhibition. The giant chloroplast repositioning is part of a complex reversible reshaping of the whole epidermal cell.

Wheat mutants with a reduced chlorophyll synthesis are affected by a defective control of the photosynthetic electron flow, but tend to recover a wild-type phenotype. The sensitivity of some mutants to light fluctuations suggested that cultivation outdoors could significantly impact productivity. Six mutant lines of Triticum durum or Triticum aestivum with their respective wild-type cultivars were cultivated with a regular seasonal cycle (October–May) in a semi-field experiment. Leaf chlorophyll content and fluorescence parameters were analysed at the early (November) and late (May) developmental stages, and checked for correlation with morphometric and grain-production parameters. The alleviation of the phenotype severity concerned primarily the recovery of the photosynthetic-membrane functionality, but not the leaf chlorophyll content. Photosystem II (PSII) was less photoprotected in the mutants, but a moderate PSII photoinhibition could help control the electron flow into the chain. The accumulation of interchain electron carriers was a primary acclimative response towards the naturally fluctuating environment, maximally exploited by the mature durum-wheat mutants. The mutation itself and/or the energy-consuming compensatory mechanisms markedly influenced the plant morphogenesis, leading especially to reduced tillering, which in turn resulted in lower grain production per plant. Consistently with the interrelation between early photosynthetic phenotype and grain-yield per plant, chlorophyll-fluorescence indexes related to the level of photoprotective thermal dissipation (pNPQ), photosystem II antenna size (ABS/RC), and pool of electron carriers (Sm) are proposed as good candidates for the in-field phenotyping of chlorophyll-deficient wheat.

The wheat lines affected by a decrease in the leaf chlorophyll content typically experience a biomass loss. A known major problem of the chlorophyll-deficient wheat mutants is their limited prevention of Photosystem I (PSI) over-reduction brought about by an insufficient cyclic electron flow, potentially exposing them to a higher sensitivity to light fluctuations. However, the resistance of some mutant lines against fluctuating light suggests the occurrence of regulatory processes compensating for the defect in cyclic electron flow. In this study, a phenotyping approach based on fast chlorophyll a fluorescence induction (OJIP transient), corroborated by P700 redox kinetics, was applied to a collection of chlorophyll-deficient wheat lines, grown under continuous or fluctuating light. Quantitative parameters calculated from the OJIP transient are considered informative about Photosystem II (PSII) functional antenna size and photochemistry, as well as the functioning of the entire photosynthetic electron transport chain. The mutants tended to recover a wild-type-like chlorophyll content, and mature plants could hardly be distinguished based on their effective PSII antenna size. Nevertheless, specific OJIP-derived parameters were strongly correlated with the phenotype severity, in particular the amplitude of the I-P phase and the I-P/J-P amplitude ratio, which are indicative of a more capacitive pool of PSI final electron acceptors (ferredoxin and ferredoxin-NADP+ oxidoreductase, FNR). We propose that the enlargement of such pool of electron carriers is a compensatory response operating at the acceptor side of PSI to alleviate potentially harmful over-reduced states of PSI. Our results also suggest that, in chlorophyll-deficient mutants, higher FV /FM cannot prove a superior PSII photochemistry and wider I-P phase is not indicative of a higher relative content of PSI.

The Lycophyte Selaginella martensii efficiently acclimates to diverse light environments, from deep shade to full sunlight. The plant does not modulate the abundance of the Light Harvesting Complex II, mostly found as a free trimer, and does not alter the maximum capacity of thermal dissipation (NPQ). Nevertheless, the photoprotection is expected to be modulatable upon long-term light acclimation to preserve the photosystems (PSII, PSI). The effects of long-term light acclimation on PSII photoprotection were investigated using the chlorophyll fluorometric method known as "photochemical quenching measured in the dark" (qP(d)). Singularly high-qP(d) values at relatively low irradiance suggest a heterogeneous antenna system (PSII antenna uncoupling). The extent of antenna uncoupling largely depends on the light regime, reaching the highest value in sun-acclimated plants. In parallel, the photoprotective NPQ (pNPQ) increased from deep-shade to high-light grown plants. It is proposed that the differences in the long-term modulation in the photoprotective capacity are proportional to the amount of uncoupled LHCII. In deep-shade plants, the inconsistency between invariable maximum NPQ and lower pNPQ is attributed to the thermal dissipation occurring in the PSII core.

Microalgae are proposed in several biotechnological fields because of their ability to produce biomass enriched in high-value compounds according to cultivation conditions. Regarding the health sector, an emerging area focuses on natural products exploitable against viruses. This work deals with the characterization of the green microalga Neochloris oleoabundans cultivated under autotrophic and mixotrophic conditions as a source of whole aqueous extracts, tested as antivirals against HCoV-229E (Coronaviridae family). Glucose was employed for mixotrophic cultures. Growth and maximum quantum yield of photosystem II were monitored for both cultivations. Algae extracts for antiviral tests were prepared using cultures harvested at the early stationary phase of growth. Biochemical and morphological analyses of algae indicated a different content of the most important classes of bioactive compounds with antiviral properties (lipids, exo-polysaccharides, and total phenolics, proteins and pigments). To clarify which phase of HCoV-229E infection on MRC-5 fibroblast cells was affected by N. oleoabundans extracts, four conditions were tested. Extracts gave excellent results, mainly against the first steps of virus infection. Notwithstanding the biochemical profile of algae/extracts deserves further investigation, the antiviral effect may have been mainly promoted by the combination of proteins/pigments/phenolics for the extract derived from autotrophic cultures and of proteins/acidic exo-polysaccharides/lipids in the case of mixotrophic ones.

Microalgae are studied as innovative sources of a wide range of highly valuable products, including proteins for the food/feed sectors. However, protein content varies depending on algal species, culture conditions and harvesting period. The Phylum Chlorophyta includes most of the described species of green algae. Due to their remarkable peculiarities, four Chlorophyta species belonging to two distinct classes were selected for the research: Chlorella vulgaris and Chlorella protothecoides as Trebouxiophyceae, and Neochloris oleoabundans and Scenedesmus acutus as Chlorophyceae. The algae were studied to obtain comparative results about their growth performance, and total protein content and profile under the same culture conditions. Since photosynthetic process directly influences biomass production, photosynthetic pigment, PSII maximum quantum yield and thylakoid protein content and profile were analysed. SDS-PAGE and 2D BN/SDS-PAGE were performed to expand information on the organization and assembly of the resolved thylakoid complexes of samples. Despite the algal species showed similar growth rates and photosynthetic efficiency, S. acutus showed the highest capability to accumulate proteins and photosynthetic pigments. Regarding the thylakoid protein profile, the two Trebouxiophyceae showed very similar pattern, whereas different amounts of LHCII occurred within the two Chlorophyceae. Finally, the separation of thylakoid protein complexes in 2D BN/SDS-PAGE revealed a more complex pattern in S. acutus as compared to the other species. Overall, it is suggested that a higher stability of the photosynthetic membranes can result in higher biomass and protein production. Altogether, results have highlighted the metabolic uniqueness of each strain, resulting in a non-obvious comparison with the other species.

In plants, the non-photochemical quenching of chlorophyll fluorescence (NPQ) induced by high light reveals the occurrence of a multiplicity of regulatory processes of photosynthesis, primarily devoted to photoprotection of photosystem I and II (PSI and PSII). The study of NPQ relaxation in darkness allows the separation of three kinetically distinct phases: the fast relaxing high-energy quenching qE, the intermediate relaxing phase and the nearly non-relaxatable photoinhibitory quenching. Several processes can underlie the intermediate phase. In the ancient vascular plant Selaginella martensii (Lycopodiophyta) this component, here termed qX, was previously proposed to reflect mainly a photoprotective energy-spillover from PSII to PSI. It is hypothesized that qX is induced by an over-reduced photosynthetic electron transport chain from PSII to final acceptors. To test this hypothesis the leaves were treated with the reductant dithiothreitol (DTT) and the chlorophyll fluorescence changes were analysed during the induction with high irradiance and the subsequent relaxation in darkness. DTT treatment caused the well-known decrease in NPQ induction and expectedly resulted in a disturbed photosynthetic electron flow. The relaxation curves of Y(NPQ), formally representing the quantum yield of the regulatory thermal dissipation, revealed a DTT dose-dependent decrease in amplitude not only of qE, but also of qX, up to the complete disappearance of the latter. Modelling of the relaxation curves under alternative scenarios led to the conclusion that DTT is permissive with respect to qX induction but suppresses its dark relaxation. The strong dependence of qX on the chloroplast redox state is discussed with respect to its proposed energy-spillover photoprotective significance in a lycophyte.

The biotechnological potential of microalgae has gained considerable importance in many applied fields: biomass production for food and feed, cosmeceutical and pharmaceutical products, energy and phytoremediation. The driving force that inspires the progress in microalgae production is the need for new cultivation systems to obtain simultaneously the maximum yield, reduction of water and nutrients use, and production of economically interesting molecules, such as pigments, fatty acids and polysaccharides. We aim to test, for the first time, the co-cultivation in saline medium of Tisochrysis lutea (Haptophyta) and Nannochloropsis oculata (Ochrophyta) to obtain valuable compounds, i.e. pigments and lipids characteristic of each species, using a single culture process. Mono-cultures of each strain were used as controls. The two strains showed an increase in the concentration of chlorophylls and carotenoids in co-culture. At the end of the experiment, the fatty acid profile was analysed by gas chromatography–mass spectrometry. The lipids in the co-cultivated cell extracts were mainly attributable to N. oculata , which represented 97% of the total cells (ca. 83% of the total biomass) at the end of the experiment. Nevertheless, the ω-3 characteristic of T. lutea (DHA and SDA, absent in N. oculata ) was also detectable. Although the co-cultivation of these two phylogenetically different species of microalgae did not show positive effects on the growth and on the total lipid production, however, this process resulted in a reduction of the production costs and a lower consumption of water and nutrients.