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Photosynthesis is a vital process for seed productivity. It occurs in the leaves and provides developing seeds with the necessary nutrients. Moreover, many crops require photochemical reactions inside the seeds for proper development. The present study aimed to investigate Pisum sativum L. seeds at the middle stage of maturation, which is characterized by the active synthesis of nutrient reserves. Embryonic photosynthesis represents a crucial process to produce cells' NADP(H) and ATP, which are necessary to convert sucrose into reserve biopolymers. However, it remains unclear how the pea embryo, covered by a coat and pericarp, receives sufficient light to provide energy for photochemical reactions. Recent studies have demonstrated that the photosynthetically active radiation reaching the developing pea embryo has a high proportion of green light. In addition, green light can be utilized in foliar photosynthesis by plants cultivated in shaded conditions. Here, we addressed the role of green light in seed development. Pea plants were cultivated under red and blue (RB) LEDs or red, green, and blue (RGB) LEDs. A Chl a fluorescence transient based on OJIP kinetics was detected at the periphery of the cotyledons isolated from developing seeds. Our findings showed that the addition of green light resulted in an increase in photochemical activity. Furthermore, the mature seeds that developed in the RGB module had a significantly higher weight and more storage proteins. Using a metabolomics approach, we also detected significant differences in the levels of organic acids, carbohydrates, nucleotide monophosphates, and nitrogenous substances between the RB and RGB conditions. Under RGB light, the cotyledons contained more ornithine, tryptophan, arginine, and aspartic acid. These changes indicate an impact of green light on the ornithine–urea cycle and polyamine biosynthesis. These results allow for a deeper understanding of the photochemical processes in embryos of developing seeds grown under a low light intensity. The photosynthetic system in the embryo cell adapts to the shade conditions by using green light. [ABSTRACT FROM AUTHOR]

Introduction: Glacier ice algae, mainly Ancylonema alaskanum and Ancylonema nordenskiöldi, bloom on Greenland Ice Sheet bare ice surfaces. They significantly decrease surface albedo due to their purple-brown pigmentation, thus increasing melt. Little is known about their metabolic adaptation and factors controlling algal growth dynamics and pigment formation. A challenge in obtaining such data is the necessity of melting samples, which delays preservation and introduces bias to metabolomic analysis. There is a need to evaluate the physiological response of algae to melting and establish consistent sample processing strategies for metabolomics of ice microbial communities. Objectives: To address the impact of sample melting procedure on metabolic characterization and establish a processing and analytical workflow for endometabolic profiling of glacier ice algae. Methods: We employed untargeted, high-resolution mass spectrometry and tested the effect of sample melt temperature (10, 15, 20 °C) and processing delay (up to 49 h) on the metabolome and lipidome, and complemented this approach with cell counts (FlowCam), photophysiological analysis (PAM) and diversity characterization. Results and Conclusion: We putatively identified 804 metabolites, with glycerolipids, glycerophospholipids and fatty acyls being the most prominent superclasses (> 50% of identified metabolites). Among the polar metabolome, carbohydrates and amino acid-derivatives were the most abundant. We show that 8% of the metabolome is affected by melt duration, with a pronounced decrease in betaine membrane lipids and pigment precursors, and an increase in phospholipids. Controlled fast melting at 10 °C resulted in the highest consistency, and is our recommendation for future supraglacial metabolomics studies. [ABSTRACT FROM AUTHOR]

The constantly growing need to increase the production of agricultural products in changing climatic conditions makes it necessary to accelerate the development of new cultivars that meet the modern demands of agronomists. Currently, the breeding process includes the stages of genotyping and phenotyping to optimize the selection of promising genotypes. One of the most popular phenotypic methods is the pulse-amplitude modulated (PAM) fluorometry, due to its non-invasiveness and high information content. In this review, we focused on the opportunities of using chlorophyll fluorescence (ChlF) parameters recorded using PAM fluorometry to assess the state of plants in drought and heat stress conditions and predict the economically significant traits of wheat, as one of the most important agricultural crops, and also analyzed the relationship between the ChlF parameters and genetic markers. [ABSTRACT FROM AUTHOR]

The availability of light and its efficient utilisation is a major limiting factor in large scale algal cultures. While algae predominantly use the blue and red spectral regions, a significant amount of incoming light energy remains untapped outside these ranges. Converting this unused light into usable wavelengths could enhance photosynthesis. This study aimed to identify the optimal spectral converter among Lumogen Red (LR), Rhodamine 8G (R8G), and Lumogen Yellow (LY), providing efficient light utilisation for algal cultivation. Chlamydomonas reinhardtii was cultivated in double-jacketed cylindrical photo-bioreactors (PBRs) using 30% UV-a and 5% UV-b fluorescent tubes. The R8G dye displayed a slight wavelength shift with a sharp peak at about 498 nm. The LY dye demonstrated several sharp peaks at the green and blue light spectra evident of photo-degradation. The LR dye maintained better photo-stability compared to R8G and LY. Carbohydrate, lipid and protein were produced early, whereas biomass increased after day 4, as a result of photo-acclimation. The LR dye converted and emitted 3.17 × 10-19 J photon-1, enhancing biomass production and increasing photochemical energy utilisation [Y(II)] while decreasing regulated energy dissipation [Y(NPQ)]. Pigment biosynthesis was initially increased and then reduced to counteract heightened irradiation as a means of photo-protection. LR had a 1.6- and 2.9-fold up-regulation of the RuBisCo gene expression. The dye-based system correlated with improved growth, lipid, protein, carbohydrate, and pigment production. The dye-based wavelength conversion system was interlinked to the sustainable development goals addressing environmental, economic, and social aspects. [ABSTRACT FROM AUTHOR]

Metal toxicity in marine ecosystems is a growing issue owing to terrestrial runoff and anthropogenic pollution. Heterocapsa cf. bohaiensis, a newly isolated dinoflagellate from New Caledonia, was cultivated in photobioreactors operating continuously with high concentrations (10-3 M) of nickel (Ni2+) and/or iron (Fe2+) and their photosynthetic efficiency was assessed. The photosynthetic measurements indicated that H. cf. bohaiensis was tolerant to Ni2+ but sensitive to Fe2+ high concentrations. In the presence of Fe2+, maximum quantum efficiency and maximal relative electron transport rate decreased from 0.62 to 0.47 and from 156 to 102, respectively. The JIP-tests suggested a reduction of the photosynthesis in response to Fe2+ due to a disruption in the electron transport chain rather than a defect in the light absorption and trapping capacity which were on the contrary enhanced by Fe2+. These results bring new knowledge on the impact of nickel and iron on microalgae photosynthetic pathways.

Many crops require not only leaf photosynthesis for their seed development but also the photochemical reactions that occur in the seeds. The purpose of this work was a comparative analysis of light transmittance and photochemical activity in the leaves of Pisum sativum L. and its pericarp, seed coat, and cotyledons at the early, middle, and late maturation stages. The spectral composition of light was measured using a spectroradiometer in the range of 390–760 nm. We assessed the light transmittance of plant tissues by placing the plant tissue between the light source and the spectroradiometer’s sensor. PAM fluorometry was used to quantify the photochemical activity in plant tissues: this technique is handy for evaluating the efficiency of converting light energy into chemical energy through the analysis of the kinetics of chlorophyll fluorescence excitation and quenching. On average, a photochemically active green leaf of pea transmitted 15 % of solar radiation in the 390–760 nm, blue light was delayed entirely, and the transmitted red light never exceeded 5 %. Photochemically active radiation passing through the pericarp and coat and reaching the cotyledons at the early and middle seed maturation stages manifested a high proportion of green and far-red light; there was no blue light, and the percentage of red light was about 2 %. However, the cotyledons were photochemically active regardless of low irradiance and spectral ranges untypical of leaf photosynthesis. At the early and middle maturation stages, the maximum quantum yield of photosystem II (Fv/Fm) averaged 0.5 at the periphery of cotyledons and 0.3 at their center. Since the intensity of embryonic photochemical reactions significantly affects the efficiency of reserve nutrient accumulation, this parameter is a promising marker in pea breeding for seeds with improved nutritional qualities.

Photosynthesis is a vital process for seed productivity. It occurs in the leaves and provides developing seeds with the necessary nutrients. Moreover, many crops require photochemical reactions inside the seeds for proper development. The present study aimed to investigate Pisum sativum L. seeds at the middle stage of maturation, which is characterized by the active synthesis of nutrient reserves. Embryonic photosynthesis represents a crucial process to produce cells’ NADP(H) and ATP, which are necessary to convert sucrose into reserve biopolymers. However, it remains unclear how the pea embryo, covered by a coat and pericarp, receives sufficient light to provide energy for photochemical reactions. Recent studies have demonstrated that the photosynthetically active radiation reaching the developing pea embryo has a high proportion of green light. In addition, green light can be utilized in foliar photosynthesis by plants cultivated in shaded conditions. Here, we addressed the role of green light in seed development. Pea plants were cultivated under red and blue (RB) LEDs or red, green, and blue (RGB) LEDs. A Chl a fluorescence transient based on OJIP kinetics was detected at the periphery of the cotyledons isolated from developing seeds. Our findings showed that the addition of green light resulted in an increase in photochemical activity. Furthermore, the mature seeds that developed in the RGB module had a significantly higher weight and more storage proteins. Using a metabolomics approach, we also detected significant differences in the levels of organic acids, carbohydrates, nucleotide monophosphates, and nitrogenous substances between the RB and RGB conditions. Under RGB light, the cotyledons contained more ornithine, tryptophan, arginine, and aspartic acid. These changes indicate an impact of green light on the ornithine–urea cycle and polyamine biosynthesis. These results allow for a deeper understanding of the photochemical processes in embryos of developing seeds grown under a low light intensity. The photosynthetic system in the embryo cell adapts to the shade conditions by using green light.

The constantly growing need to increase the production of agricultural products in changing climatic conditions makes it necessary to accelerate the development of new cultivars that meet the modern demands of agronomists. Currently, the breeding process includes the stages of genotyping and phenotyping to optimize the selection of promising genotypes. One of the most popular phenotypic methods is the pulse-amplitude modulated (PAM) fluorometry, due to its non-invasiveness and high information content. In this review, we focused on the opportunities of using chlorophyll fluorescence (ChlF) parameters recorded using PAM fluorometry to assess the state of plants in drought and heat stress conditions and predict the economically significant traits of wheat, as one of the most important agricultural crops, and also analyzed the relationship between the ChlF parameters and genetic markers.

Photosynthesizers face a trade-off regarding light: they need enough to maintain high photosynthetic rates, yet excess leads to oxidative stress. Despite this, light and its detrimental effects are chronically underestimated. Solar-powered sea slugs (Sacoglossa: Gastropoda) provide the ideal lens with which to study this trade-off, since they steal chloroplasts from algae but do not inherit photoacclimation and photorepair capacities. We collected three slug species in Curaçao during March and December 2022, comparing the amount of light they received in nature to their optimal light intensities for photosynthesis, and their preferred light intensities. We then investigated behavioral and physiological photoprotection mechanisms to determine if and how they limit light. Finally, we examined oxidative activity under optimal and excess light. All three species were naturally exposed to more light (> 1000 µmol m−2 s−1) than is optimal or preferred. Elysia crispata (kleptoplast retention for > 3 months) is fully exposed to light in nature but reduces the light reaching its kleptoplasts via parapodial shading. Elysia velutinus retains kleptoplasts for ~ 2 weeks and hides in its macroalgal food, limiting light exposure. Both species displayed low amounts of oxidative activity under optimal light, which increased slightly under excess light. Elysia ornata retained chloroplasts for ~ 3 days, lacked observable photoprotection and always displayed high levels of oxidative activity, potentially explaining its limited capacity for kleptoplast retention. Furthermore, both E. velutinus and E. ornata display strong light-avoidance behaviors. This study clearly demonstrates links between high light intensities, photoprotection, and oxidative stress, highlighting the need for future studies that examine aquatic photosynthesizers under natural lighting. [ABSTRACT FROM AUTHOR]

The TvV-SM2 virus, isolated fromthe coastal waters of the Black Sea, causes lysis of its host, the algae Tetraselmis viridis (Chlorophyta). Under optimal conditions for nutrients, an increase in the initial abundance of algae cells by four times caused a 3-fold reduction in the latent period of viral infection. During the period of the most rapid cell lysis of T. viridis, nitrogen deficiency leads to a decrease in the average daily rate of death of cells affected by the virus by 3.2 times relative to the replete conditions, while in the case of phosphorus deficiency, this process slows down by up to 2.4 times. Under deplete conditions, the rate of cell death was only 34% lower than under replete conditions. The effect of copper ions (100 µg L-1) on the viral suspension for 6 h led to the complete suppression of its activity. In the presence of the host of this virus, its activity is only partially suppressed. As a result, cell lysis under the influence of a viral infection occurred in two stages. The first stage was noted only during the first 6 h of the experiment. The second main stage took place within 78-170 h. This study showed that in conditions of nutrient deficiency and in the presence of copper ions in seawater, the impact of viruses on microalgae will be weaker. [ABSTRACT FROM AUTHOR]

Environmental variation has a significant impact on how organisms, including cyanobacteria, respond physiologically and biochemically. Salinity and ultraviolet radiation (UVR)-induced variations in the photopigments of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21 and its photosynthetic performance was studied. We observed that excessive energy dissipation after UVR is mostly caused by Non-Photochemical Quenching (NPQ), whereas photochemical quenching is important for preventing photoinhibition. These findings suggest that ROS production may play an important role in the UVR-induced injury. To reduce ROS-induced oxidative stress, Nostochopsis lobatus HKAR-21 induces the effective antioxidant systems, which includes different antioxidant compounds like carotenoids and enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). The study indicates that Nostochopsis lobatus HKAR-21 exposed to photosynthetically active radiation + UV-A + UV-B (PAB) and PAB + NaCl (PABN) had significantly reduced photosynthetic efficiency. Furthermore, maximum ROS was detected in PAB exposed cyanobacterial cells. The induction of lipid peroxidation (LPO) has been investigated to evaluate the impact of UVR on the cyanobacterial membrane in addition to enzymatic defensive systems. The maximal LPO level was found in PABN treated cells. Based on the findings of this research, it was concluded that salinity and UVR had collegial effects on the major macromolecular components of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21. [ABSTRACT FROM AUTHOR]

The influence of six experimental light sources (lamps) based on LEDs with different emission spectra simulating optical radiation close to solar radiation on the photochemical activity of photosystems (PS) of purple basil leaves and on the redox state of the P700 reaction center was studied. The spectra differed in the photon flux distribution over the main emission spectrum ranges, correlated color temperature (CCT), and general color rendering index (Ra). A comparative analysis of PAM fluorometry parameters resulted in the identification of the spectral regions that ensure more efficient photosynthetic processes in basil leaf cells at stages of technical ripening and flowering. In particular, basil plants grown on a spectrum with a CCT of 5260 K and Ra 98 had a fairly low F0 level, one of the highest Fv/Fm ratios characteristic of plants under nonstressful conditions, one of the highest quantum yields of both PS Y(I) and Y(II), and high electron flow rates. Spectra with CCT 4550 K and Ra 91 and with CCT 2820 K and Ra 81 also looked promising in terms of PAM fluorometry parameters. The spectrum with CCT 2990 and Ra 97 had the worst performance in terms of the studied PSI and PSII parameters. [ABSTRACT FROM AUTHOR]

Metal toxicity in marine ecosystems is a growing issue owing to terrestrial runoff and anthropogenic pollution. Heterocapsa cf. bohaiensis, a newly isolated dinoflagellate from New Caledonia, was cultivated in photobioreactors operating continuously with high concentrations (10-3 M) of nickel (Ni2+) and/or iron (Fe2+) and their photosynthetic efficiency was assessed. The photosynthetic measurements indicated that H. cf. bohaiensis was tolerant to Ni2+ but sensitive to Fe2+ high concentrations. In the presence of Fe2+, maximum quantum efficiency and maximal relative electron transport rate decreased from 0.62 to 0.47 and from 156 to 102, respectively. The JIP-tests suggested a reduction of the photosynthesis in response to Fe2+ due to a disruption in the electron transport chain rather than a defect in the light absorption and trapping capacity which were on the contrary enhanced by Fe2+. These results bring new knowledge on the impact of nickel and iron on microalgae photosynthetic pathways. [ABSTRACT FROM AUTHOR]

The microalga, Dunaliella salina, is a treasure of fine chemicals, carotenoids, and lipids of industrial importance. The present investigation focused on the maximization of lipid content in the context of biofuel. Mixotrophic cultures growing in different combinations of sodium bicarbonate (NaHCO3) and glucose (Glu) or sodium acetate (Na-Ace) were monitored for essential growth parameters such as photosynthesis, dry biomass, and Chl a content. The maximum photosynthetic quantum yield (Fv/Fm) of all the screened mixotrophic cultures along with control ranged between 0.63 and 0.72, indicating the cells were in a good physiological state. The highest biomass productivity (33.46 ± 0.58 mg/L/d) was recorded in 1.0 mM NaHCO3 + 1.0 mM Glu-containing cultures. However, the highest lipid content (56% DCW) was recorded in 1.0 mM NaHCO3 + 0.5 mM Na-Ace-containing cultures. Interestingly, a 1.7-fold higher starch content (72.3 μg/mL) was recorded in 0.25 mM NaHCO3 + 0.5 mM Na-Ace over 1.0 mM NaHCO3 + 0.5 mM Na-Ace-containing cultures. Thus, data indicated that the higher concentration of NaHCO3 along with Na-Ace favoured lipid biosynthesis, while the lower concentration of NaHCO3 with Na-Ace favoured starch synthesis. Thus, substrate provision determined the desired products. Lipids obtained from D. salina at stage II (nitrogen-deficient condition) possessed ideal fuel properties according to international standards of EN 14214 and ASTM D6751. Therefore, the present work explored the threshold level of bicarbonate along with Na-Ace which was able to maintain good physiological status and produced higher lipids with better biodiesel properties. [ABSTRACT FROM AUTHOR]

Red coralline algae are the deepest living macroalgae, capable of creating spatially complex reefs from the intertidal to 100+ m depth with global ecological and biogeochemical significance. How these algae maintain photosynthetic function under increasingly limiting light intensity and spectral availability is key to explaining their large depth distribution. Here, we investigated the photo- and chromatic acclimation and morphological change of free-living red coralline algae towards mesophotic depths in the Fernando do Noronha archipelago, Brazil. From 13 to 86 m depth, thalli tended to become smaller and less complex. We observed a dominance of the photo-acclimatory response, characterized by an increase in photosynthetic efficiency and a decrease in maximum electron transport rate. Chromatic acclimation was generally stable across the euphotic-mesophotic transition with no clear depth trend. Taxonomic comparisons suggest these photosynthetic strategies are conserved to at least the Order level. Light saturation necessitated the use of photoprotection to 65 m depth, while optimal light levels were met at 86 m. Changes to the light environment (e.g. reduced water clarity) due to human activities therefore places these mesophotic algae at risk of light limitation, necessitating the importance of maintaining good water quality for the conservation and protection of mesophotic habitats. [ABSTRACT FROM AUTHOR]

As a result of several anthropogenic factors, Cystoseira sensu lato forests have declined or become regionally extinct in many coastal regions of the Mediterranean. Given the low natural recovery of lost populations, research efforts have been encouraged to develop sustainable and efficient restoration of macroalgal forests on a large scale. By promoting growth and fertility of collected thallus branches under controlled laboratory conditions, the availability of seedlings for restoration could be ensured without jeopardizing natural populations. Here we investigated the effect of a commercial algal biostimulant (AlgatronCifo®) on the photophysiology, growth and fertility of Gongolaria barbata (Stackhouse) Kuntze (Fucales, Phaeophyceae). In a factorial laboratory experiment, two different temperatures (10 ºC and 14 °C) and two culture media [i.e. seawater (SW) and Algatron (AT)] were tested. The photosynthetic performance of G. barbata doubled after three weeks of culture with AT, while it decreased by 25% when cultivated in SW. The highest photosynthetic performance and growth were achieved at 14ºC with AT, where fertile receptacles also developed, followed by seedling settlements. The thalli cultured in AT had similar or better photosynthetic performance than the initial control thalli. AT-cultured thalli had a greater ability to quench energy via photochemical pathways (qP) than those from the SW, which on the contrary, had higher levels of non-photochemical responses (qN, NPQmax). This limited photosynthetic performance was probably linked to the higher P-limitation experienced under that treatment. The algal biostimulant enhanced the physiological performance and induced fertility of G. barbata, demonstrating its valorization potential and setting a new path for improved restoration applications. [ABSTRACT FROM AUTHOR]

According to the action spectrum of photosynthesis, photosynthetic efficiency is highest for red light. However, long-term growth with only red light leads to unfavorable changes in plant morphology, decrease in photosynthetic capacity and plant productivity. Detailed mechanisms behind these changes are still poorly understood. We studied the effects of narrow-band red (RL) and blue (BL) LED lighting on the morphology and photosynthesis of barley (Hordeum vulgare L.) seedlings at 9 days old, when energy for plant growth comes mostly from the endosperm, and light has a mainly morphogenic effect on plant growth. Plants grown with white fluorescent lamps (WL) were used as a control. At this developmental stage, light spectrum had small but significant effects on most morphometric parameters, which may become more prominent as the plant grows. These effects were more pronounced in RL-grown plants and were similar to the 'shade-avoidance response', which is unusual as in nature it occurs when the fraction of red light in the spectrum is low. RL-grown plants also had impaired photosynthetic photochemical efficiency (as assessed by PAM-fluorometry and leaf absorption). BL-grown plants had a stronger similarity to control plants in their morphology and photosynthetic characteristics than RL-grown plants; however, they had higher NPQ and different NPQ induction kinetics than WL- and RL-grown plants. Our results suggest that photoregulation of plant morphology and photosynthesis evolutionarily adapted to natural light is miscoordinated in narrow-band LED light. We discuss possible reasons for this miscoordination and for the formation of observed phenotypes on the level of photoreceptors. [ABSTRACT FROM AUTHOR]

In the environment algae are exposed to non-optimal conditions and adapt their physiology to cope with adverse circumstances, such as limiting nutrients or excess contaminants. The present study evaluated the changes in photosynthetic parameters and lipid classes of the freshwater green microalga Ankistrodesmus densus exposed to nitrogen (N) limitation and cadmium (Cd) exposure. While N is required for algal metabolism, Cd does not present known functions in freshwater microalgae. Regarding the isolated stressors, our results indicate that N and Cd affected the growth rate, chlorophyll a production, the maximum quantum yield and increased the percentage of storage lipids (triacylglycerol—TAG). The quenchings, i.e., fractions of light energy driven to photochemical or non-photochemical processes of photosynthesis, were only affected by Cd. However, in the combination of the two stressors, the changes were more pronounced, with synergism in the growth rate, photochemical quenching (qP), and effective quantum yield ((Y(II)). Concerning lipid classes, there were non-linear changes in the percentages of TAG. At the highest combinations of Cd and N, it was observed a tendency of antagonism in the structural lipids (phospholipids, PL) and to synergism in acetone mobile polar lipids. Our data indicate that combining the two stressors affected algal physiology with synergism in several parameters. However, the algal photoprotective mechanisms effectively avoided photodamage, as indicated by non-photochemical quenchings (qN and NPQ) and in the quantum yield related to regulated energy loss ((Y (NPQ)) values. The tendency to antagonism in PL on the combination of the highest concentrations of Cd and N limitation can indicate the investment in structural lipids to avoid metal internalization. [ABSTRACT FROM AUTHOR]

Extreme seawater temperatures are linked to increasingly frequent cnidarian bleaching, a breakdown of the symbiosis between host and endosymbiotic dinoflagellates. This can be driven by several anthropogenic stressors, of which seawater warming is a major and frequent one. It remains unclear whether this is caused by intrinsic properties of the host or exclusively by the symbiont. This study investigates the response to elevated temperatures of dinoflagellate symbionts in and ex hospite, particularly to find out whether thermal tolerance differs between endosymbionts and free-living micro-algae. Maximum quantum yield of photosystem II (Fv/Fm) and symbiont cell density were measured in seven different cnidarian species and five cultures of isolated endosymbionts subjected to temperatures of 26°C (control), 30°C and 34°C for 21 days. Isolated dinoflagellate cells showed a susceptibility to elevated temperatures of 30°C, evidenced by a decrease in photochemical efficiency and cell density of the cultures, as well as a progressive disintegration of cellular structures and loss of pigmentation of all but two cultures during the first week of exposure. Bleaching of coral holobionts at 30°C could be explained by reduced density of algae cells in host tissue. This effect was particularly evident in soft corals. Exposure to 34°C resulted in drastic bleaching of stony coral species, anemones and jellyfish, and even the death of soft corals. Data from this study show different responses to elevated thermal conditions across several species and different genera of symbionts and emphasize the important role of dinoflagellate symbionts in the holobiont response to elevated seawater temperatures. [ABSTRACT FROM AUTHOR]

Microalgal bioassays were conducted to evaluate the ecotoxicological effects of suspended sediments (SS) collected from coastal environments. Growth inhibition was assessed for six microalgal species, and multiple endpoints were measured using flow cytometry (FCM) and pulse-amplitude modulation (PAM) fluorometry for three species (Dunaliella tertiolecta , Isochrysis galbana , and Phaeodactylum tricornutum). Among these, the EC50 for growth inhibition of D. tertiolecta (6700 mg L−1) was notably lower compared to the other species, and among several endpoints, esterase activity was the most inhibited. Species-specific responses to SS exposure were identified, with D. tertiolecta exhibiting greater susceptibility across most endpoints. Meanwhile, measurements of Fo', Fm', and Y(NPQ) in P. tricornutum using PAM fluorometry revealed greater sensitivity. Based on the results of this study and review, the tentative predicted no-effect concentration was calculated as 12.1 mg L−1. Overall, this study provides novel insights into SS ecotoxicity, establishing a crucial baseline for future investigations. [Display omitted] • Microalgal bioassays were used to evaluate the ecotoxicity of suspended sediment (SS). • Exposure of SS specifically reduced esterase activity in D. tertiolecta. • SS affects photosynthesis in microalgae by altering the energy dissipation of PSII. • The hazardous concentration for 5 % of species (HC5) to SS was derived to be 61 mg L−1. • The tentative predicted no-effect concentration (PNEC) was calculated as 12.1 mg L−1. [ABSTRACT FROM AUTHOR]

A Reflectance Absorptance Transmittance (RAT) meter, developed for routine measurements of Abtλ nm on leaves, was used to measure absorptance of algal films mounted on glass fibre filter disks for use in PAM (Pulse Amplitude Modulation) fluorometry. Absorptance readings (Abtλ nm) are essential to quantitate the photosynthetic electron transport rate from PAM data and are also helpful if algal disks are used in an IRGA (InfraRed Gas Analyzer). Measurements were made on Synechococcus R-2 (Cyanophyceae), Acaryochloris marina (Chlorobacteria), Chlorella vulgaris (Chlorophyceae), Chaetoceros sp. (Bacillariophyceae) and Isochrysis sp. (Haptophyta) in blue (445 nm), green (525 nm) and red (625 nm) light. Plots of Abtλ vs. Chl a (mg Chl a m-2) or Chl d for Acaryochloris (mg Chl d m-2) of the algae followed exponential saturation curves (Abt%λ = Abt%λ, ∞ (1-e-k×Chl)) usually reaching asymptotes in the blue light used by blue-diode PAM machines. Synechococcus, Chlorella, Chaetoceros and Isochrysis Abt%445nm saturates ≈ 50-100 mg Chl a m-2 (Synechococcus: Abt%445 nm, max = 77.3±0.94, ±95% conf. limits, Chlorella: Abt%445 nm, max = 77.0±2.06, Chaetoceros: Abt%445 nm, max = 80.6±1.87; Isochrysis: 83.2±8.06 mg Chl a m-2); Acaryochloris above about 100 mg Chl d m-2. Asymptotic loading of cells was in general easily achieved in blue light in the case of Synechococcus, Chlorella and Acaryochloris but not in green, red or "white" light. It was difficult to achieve asymptotic loading for Chaetoceros and Isochrysis due to mucilaginous blockage of the filter disks. [ABSTRACT FROM AUTHOR]

Assessing thermal tolerance of marine organisms is a prerequisite to predict their responses to upcoming warming scenarios, but thermal sensitivities broadly vary among life stages and seasons due to thermal acclimation. This study aimed to identify changes in photosynthetic performance of recruits of the intertidal canopy-forming seaweed Fucus guiryi in relation to seasonality during early ontogeny. Zygotes were isolated from late summer (LS) and late winter (LW) thalli and were exposed to an ecologically relevant thermal range (15, 20, 23 and 25°C) under laboratory-controlled conditions for 3 weeks. Photosynthetic responses were assessed by in vivo chlorophyll a fluorescence measurement. Seasonality had a significant influence on initial zygote morphology, with a decrease in area of 17% from LS to LW. Zygotes from LS and LW exhibited the typical photosynthetic responses of sun and shade plants, respectively, with a greater capacity to dissipate heat via non-photochemical quenching in LW. Late winter embryos showed a wider optimal thermal range for photosynthesis (15–23°C) than late summer ones (20–23°C). Embryos attained maximum photosynthetic responses 1 week after fertilization when they developed the apical meristem. Seasonal differences were more evident during early ontogenesis (0–14 d) than once their photosynthetic apparatus become like that of adult thalli. This study evidenced that zygote traits can vary across seasons, but zygotes are able to acclimate their photosynthetic performance up to 25°C within 3 weeks. Recruits of F. guiryi possessed a wide photosynthetic plasticity and are probably able to persist in populations close to their thermal limits if thermal thresholds are not exceeded. [ABSTRACT FROM AUTHOR]

This study documents the first validation of the suitability of the most common parameters and protocols used in marine ecophysiology to characterise photosynthesis by means of chlorophyll a fluorescence tools. We demonstrate that the effective yield of PSII (ΔF/Fm') is significantly underestimated when using short inductions times (≤1 min) following the rapid light curve protocol (RLC). The consequent electron transport rates (ETR) underestimations are species-specific and highly variable with irradiance and the photoacclimatory condition of the sample. Our analysis also questions the use of relative descriptors (relETR), as they not only overestimate photosynthesis, but overlook one of the fundamental components of the photosynthetic response: light absorption regulation. Absorptance determinations were fundamental to characterise the ETR response of low-pigmented seagrass leaves, and also uncovered relevant differences between two coral species and the accclimatory response of a cultured dinoflagellate to temperature. ETR and oxygen evolution determinations showed close correlations for all organisms tested with the expected slope of 4 e- per O2 molecule evolved, when correct photosynthesis inductions and light absorption determinations were applied. However, ETR curves cannot be equated to conventional photosynthetic response to irradiance (P vs E ) curves, and caution is needed when using ETR to characterise photosynthesis rates above photosynthesis saturation (Ek). This validation strongly supports the utility of fluorescence tools, underlining the need to correct two decades of propagation of erroneous concepts, protocols and parameters in marine eco-physiology. We aim also to emphasise the importance of optical descriptions for understanding photosynthesis, and for interpreting fluorescence measurements. In combination with conventional gross photosynthesis (GPS) approaches, optical characterisations open an extraordinary opportunity to determine two central parameters of photosynthesis performance: the quantum yield (φmax) of the process and its minimum quantum requirements (1/φmax). The combination of both approaches potentiates the possibilities of chlorophyll a fluorescence tools to characterise marine photosynthesis biodiversity. [ABSTRACT FROM AUTHOR]

Increasing levels of greenhouse gases lead to ocean warming, which affects a range of marine organisms. Corals live in a narrow temperature range and become stressed when the temperatures change. Bleaching occurs when the temperature exceeds the coral's threshold, and can be severe when this is combined with other stressors such as light. In order to understand how temperature and light affect corals in their physiological responses and photosynthetic performance, Pocillopora acuta from Maiton Island (MT) and Panwa Cape (PW), representing different environments, were investigated. The results show that light and temperature had by regime different effects on Symbiodiniaceae photosynthesis and the coral growth rate. There was a synergistic effect of elevated temperature and light on photosynthesis, as observed in the photochemical efficiency and pigment contents, suggesting photo-damage. A higher growth rate in Panwa corals was observed in control, and while elevated temperature reduced coral growth. Elevated temperature affected the Panwa coral less, suggesting that corals from this regime might be able to recover when the temperature returns to normal. This information is important for predicting the coral responses to elevated temperature especially in the summer, as regards the possibility of coral bleaching. [ABSTRACT FROM AUTHOR]

Karenia mikimotoi is a toxic bloom-forming dinoflagellate that sometimes co-blooms with Karenia brevis in the Gulf of Mexico, especially on the West Florida Shelf where strong vertical temperature gradients and rapid changes in nitrogen (N) can be found. Here, the short-term interactions of temperature, N form, and availability on photosynthesis-irradiance responses were examined using rapid light curves and PAM fluorometry in order to understand their interactions, and how they may affect photosynthetic yields. Cultures of K. mikimotoi were enriched with either nitrate (NO3), ammonium (NH4 +), or urea with varying amounts (1, 5, 10, 20, 50 μM-N) and then incubated at temperatures of 15, 20, 25, 30 °C for 1 h. At 15-25 °C, fluorescence parameters (Fv/Fm, rETR) when averaged for all N treatments were comparable. Within a given light intensity, increasing all forms of N concentrations generally led to higher photosynthetic yields. Cells appeared to dynamically balance the "push" due to photon flux pressure and reductant generation, with consumption in overall metabolism ("pull" due to demand). However, at 30 °C, all fluorescence parameters declined precipitously, but differential responses were observed depending on N form. Cells enriched with urea at 30 °C showed a smaller decline in fluorescence parameters than cells treated with NO3 or NH4 +, implying that urea might induce a photoprotective mechanism by increasing metabolic "pull". [ABSTRACT FROM AUTHOR]

Structural colour occurs when nanoscale structures interfere with incident light transmission and reflect particular wavelengths. The brown alga Ericaria selaginoides (Fucales, Phaeophyceae) has an opalescent photonic crystal anatomy that creates the blue colour of this seaweed but which responds to light, leading to speculation that the crystals have a photosynthetic role by modifying light transmission. Here, we characterize the colour response of E. selaginoides using time-lapse photography to capture responses to light treatments of different timing, duration, intensity and spectrum. The amount of light drove the colour response, with the most intense blue found in the dark which reduced rapidly in strong light and was not spectrum dependent. Chlorophyll a fluorometry showed that the maximum quantum efficiency of photosynthesis coincided with strong blue colouration but was reduced over two to three hours of illumination. This supports opalescent photonic crystals having a photosynthetic role by regulating light transmission to chloroplasts. Studies such as this could be used to improve solar cell efficiency and increase crop yield through the use of bio-inspired self-tuning mechanisms to optimize light transmission.

Water quality deterioration is expected to worsen the light conditions in shallow coastal waters with increasing human activities. Temperate seagrasses are known to tolerate a highly fluctuating light environment. However, depending on their ability to adjust to some decline in light conditions, decreases in daily light quantity and quality could affect seagrass physiology, productivity, and, eventually, survival if the Minimum Quantum Requirements (MQR) are not reached. To better understand if, how, and to what extent photosynthetic adjustments contribute to light acclimation, eelgrass (Zostera marina L.) shoots from the cold temperate St. Lawrence marine estuary (Rimouski, QC, Canada) were exposed to seven light intensity treatments (6, 36, 74, 133, 355, 503, and 860 μmol photons m–2 s–1, 14:10 light:dark photoperiod). Photosynthetic capacity and efficiency were quantified after five and 25 days of light exposure by Pulse Amplitude Modulated (PAM) fluorometry to assess the rapid response of the photosynthetic apparatus and its acclimation potential. Photoacclimation was also studied through physiological responses of leaves and shoots (gross and net primary production, pigment content, and light absorption). Shoots showed proof of photosynthetic adjustments at irradiances below 200 μmol photons m–2 s–1, which was identified as the threshold between limiting and saturating irradiances. Rapid Light Curves (RLC) and net primary production (NPP) rates revealed sustained maximal photosynthetic rates from the highest light treatments down to 74 μmol photons m–2 s–1, while a compensation point (NPP = 0) of 13.7 μmol photons m–2 s–1 was identified. In addition, an important package effect was observed, since an almost three-fold increase in chlorophyll content in the lowest compared to the highest light treatment did not change the leaves' light absorption. These results shed new light on photosynthetic and physiological processes, triggering light acclimation in cold temperate eelgrass. Our study documents an MQR value for eelgrass in the St. Lawrence estuary, which is highly pertinent in the context of conservation and restoration of eelgrass meadows. [ABSTRACT FROM AUTHOR]

Chroodactylon ornatum is a cosmopolitan non-Florideophycean red alga with a simple morphology, generally described as a euryhaline species. Herein, we compared the response of a marine strain under exposure to different salinities (3, 7.5, 15 and 30 psu) through the analyses of growth, morphology, chlorophyll a fluorescence, floridean starch properties, and mucilage composition. In 3 psu, the cultures consisted of solitary cells whereas the typical pseudofilamentous morphology of increasing length was found at higher salinities. The species grew in the whole range of salinities, although growth response together with photosynthetic efficiency were maximum in full seawater. The maximum relative electron transport rate (rETR) was significantly lower under hyposaline conditions, concomitant with the increase in photophysical decay but not in non-photochemical quenching of chlorophyll fluorescence (NPQ). Higher phycocyanin content at the highest salinity tested (30 psu) could be related to a more efficient energy transfer to the reaction centre. The amylopectin:amylose ratios were higher in 7.5 and 30 psu. Agarans extracted at different salinities showed similar sulphation degrees, but there was an increase in xylose content in the mucilage from lower salinities. This could be related to a change in physical properties of the sheath polysaccharide, yielding a polymer with lower gelling capacity which hampered the formation and/or elongation of pseudofilaments. [ABSTRACT FROM AUTHOR]

Water quality deterioration is expected to worsen the light conditions in shallow coastal waters with increasing human activities. Temperate seagrasses are known to tolerate a highly fluctuating light environment. However, depending on their ability to adjust to some decline in light conditions, decreases in daily light quantity and quality could affect seagrass physiology, productivity, and, eventually, survival if the Minimum Quantum Requirements (MQR) are not reached. To better understand if, how, and to what extent photosynthetic adjustments contribute to light acclimation, eelgrass (Zostera marina L.) shoots from the cold temperate St. Lawrence marine estuary (Rimouski, QC, Canada) were exposed to seven light intensity treatments (6, 36, 74, 133, 355, 503, and 860 μmol photons m–2 s–1, 14:10 light:dark photoperiod). Photosynthetic capacity and efficiency were quantified after five and 25 days of light exposure by Pulse Amplitude Modulated (PAM) fluorometry to assess the rapid response of the photosynthetic apparatus and its acclimation potential. Photoacclimation was also studied through physiological responses of leaves and shoots (gross and net primary production, pigment content, and light absorption). Shoots showed proof of photosynthetic adjustments at irradiances below 200 μmol photons m–2 s–1, which was identified as the threshold between limiting and saturating irradiances. Rapid Light Curves (RLC) and net primary production (NPP) rates revealed sustained maximal photosynthetic rates from the highest light treatments down to 74 μmol photons m–2 s–1, while a compensation point (NPP = 0) of 13.7 μmol photons m–2 s–1 was identified. In addition, an important package effect was observed, since an almost three-fold increase in chlorophyll content in the lowest compared to the highest light treatment did not change the leaves’ light absorption. These results shed new light on photosynthetic and physiological processes, triggering light acclimation in cold temperate eelgrass. Our study documents an MQR value for eelgrass in the St. Lawrence estuary, which is highly pertinent in the context of conservation and restoration of eelgrass meadows.

We investigated the effects of photosynthetically active radiation (PAR) and temperature on the photosynthesis of juvenile (JS) and mature sporophytes (MS) of a temperate edible brown alga Undaria pinnatifida cultivated in northeastern Japan, using optical dissolved oxygen sensors and pulse amplitude modulation (PAM)–chlorophyll fluorometry. Photosynthesis–PAR experiments at 8, 15, and 22 °C revealed that the maximum net photosynthesis differed with temperature. Values for compensation and saturation PAR indicated a high affinity for a low-light environment. The photosynthetic response of U. pinnatifida to temperature revealed an optimum temperature for oxygenic photosynthesis of 18 °C, which was lower than other laminarian kelps and inconsistent with the wide distribution range of this U. pinnatifida. High temperature and irradiance tolerance differed between MS and JS. Notably, Fv/Fm of MS remained above 0.5 at 28 °C after 168 h of incubation under dark conditions, whereas Fv/Fm was reduced to 0 for the juveniles. Six hours of constant exposure to 200 (low) and 1000 μmol (high) photons m−2 s−1 at 8, 15, and 22 °C induced chronic photoinhibition in all both MS and JS. In contrast to MS, the JS did not recover from photoinhibition in either of the PAR treatments, regardless of a period of darkness. The physiological performance of U. pinnatifida sporophytes indicate an affinity to low light, especially for JS. We expect that these finding will lead to further improvements in commercial production methods to prevent the withering of juvenile sporophytes. [ABSTRACT FROM AUTHOR]

Pharmaceuticals are produced to inflict a specific physiological response in organisms. However, as only partially metabolized after administration, these types of compounds can also originate harmful side effects to non-target organisms. Additionally, there is still a lack of knowledge on the toxicological effects of legacy pharmaceuticals such as the antibiotic azithromycin. This macrolide occurs at high concentrations in the aquatic environment and can constitute a threat to aquatic organisms that are at the basis of the aquatic food chain, namely microalgae. This study established a high‐throughput methodology to study the toxicity of azithromycin to the freshwater microalga Raphidocelis subcapitata. Flow cytometry and pulse amplitude modulated (PAM) fluorometry were used as screening tools. General toxicity was shown by effects in growth rate, cell size, cell complexity, cell viability and cell cycle. More specific outcomes were indicated by the analysis of mitochondrial and cytoplasmatic membrane potentials, DNA content, formation of ROS and LPO, natural pigments content and photosystem II performance. The specific mode of action (MoA) of azithromycin to crucial components of microalgae cells was revealed. Azithromycin had a negative impact on the regulation of energy dissipation at the PSII centers, along with an insufficient protection by the regulatory mechanisms leading to photodamage. The blockage of photosynthetic electrons led to ROS formation and consequent oxidative damage, affecting membranes and DNA. Overall, the used methodology exhibited its high potential for detecting the toxic MoA of compounds in microalgae and should be considered for future risk assessment of pharmaceuticals.

We examined the effects of four stressors, irradiance, temperature, desiccation, and salinity on the photosynthesis of a red alga, Agarophyton vermiculophyllum (= Gracilaria vermiculophylla, Gracilariales, Rhodophyta) from its native distributional range in Hokkaido and Kagoshima, Japan. Photosynthesis–irradiance (P–E) curves at 8, 16, and 28°C showed that the maximum net-photosynthetic rates (NPmax) and saturation irradiance (Ek) were highest at 28°C for both strains. Gross-photosynthesis determined at 8–40°C at 200 μmol photons m-2 s-1 showed that the maximum gross-photosynthetic rate (GPmax) occurred at 25.3°C for Hokkaido and 28.0°C for Kagoshima ( T opt GP ), which is almost consistent with the summer-time seawater temperature at each habitat. The temperature responses (4–40°C) of effective quantum yields (ΔF/Fm') of photosystem II during 7-day exposures were similar to that of oxygenic photosynthesis and the optimum temperature ( T opt ΔF / Fm ′ ) was 20.0°C for Hokkaido and 30.1°C for Kagoshima. In the desiccation experiment, the ΔF/Fm' decreased with decreasing absolute water content (AWC); nevertheless, for samples with an AWC above 20%, ΔF/Fm' retuned to initial levels after subsequent 1-day rehydration in seawater, suggesting relatively strong tolerance to desiccation. This alga also showed a broad range of tolerance to salinity ranging from 20 to 60 psu in 7-day exposures, and the ΔF/Fm' tolerated 0 psu at 3-day exposure. The adaptations of A. vermiculophyllum from its native range in Japan to relatively high irradiance, a broad range of temperature, and strong osmotic (desiccation and salinity) tolerance explain its potentially high invasive capacity. [ABSTRACT FROM AUTHOR]

The impact of concrete composition and roughness on the formation of microalgal biofilms and their photobiology were studied on marine infrastructures presenting four different compositions combined with two degrees of roughness (rough and smooth). The structures were first inoculated with a natural microphytobenthic biofilm and immersed in sterilised seawater with a controlled photoperiod for six days. Photosynthetic activity was assessed with an imaging PAM-(Pulse Amplitude Modulated) fluorometer and microtopography was monitored in parallel with a 3-D camera. The results indicated that roughness had an impact on the biofilm biomass, its physiological status and its photosynthetic efficiency and capacity. The assessment of surface roughness indicated that negative reliefs were preferably colonised by MPB (microphytobenthic) cells with better photosynthetic performances. Moreover, MPB biofilms showed better photoacclimation in these microhabitats than on the positive and smooth reliefs. This study confirms the importance of microhabitat for biofilm formation and their photobiology. [ABSTRACT FROM AUTHOR]

Two morphologically similar digitate kelp species, Laminaria digitata and Hedophyllum nigripes, co-occur along a shallow sublittoral depth gradient in the Arctic but, in contrast to L. digitata, very few ecophysiological data exist for H. nigripes. We investigated growth, survival, photosynthetic characteristics and carbon:nitrogen ratios of juvenile sporophytes, and recruitment and survival of gametophytes in genetically verified Arctic isolates of both species along temperature gradients (0–25 °C) over 14 days. Laminaria digitata gametophytes survived 23–24 °C, while sporophytes survived 21–22 °C. Hedophyllum nigripes had lower temperature affinities. Gametophytes survived 19–21 °C, while sporophytes survived 18 °C. Male gametophytes were more heat-tolerant than female gametophytes in both species. The pronounced cold adaption of H. nigripes compared to L. digitata also became apparent in different sporophyte growth optima (L. digitata: 15 °C; H. nigripes: 10 °C) and gametogenesis optima (L. digitata: 5–15 °C; H. nigripes: 0–10 °C). Higher carbon:nitrogen ratios in H. nigripes suggest an adaptation to nutrient poor Arctic conditions. The overall temperature performance of H. nigripes possibly restricts the species to Arctic–Sub-Arctic regions, while Arctic L. digitata behaved similarly to cold-temperate populations. Our data suggest that a future increase in seawater temperatures may hamper the success of H. nigripes and favour L. digitata in Arctic environments. [ABSTRACT FROM AUTHOR]

Macrophytes play an important role in providing habitat structure, nutrient cycling and improvement of water quality in freshwater ecosystems. However, increasing human population and the industrial revolution during past several centuries have increased the utilization of natural resources and have caused strong changes in the structure and function of the environment, such as high sedimentation that decreases light penetration. This study investigated the effects of in situ experimental shading on photosynthetic performance of submerged Elodea canadensis macrophytes and identified the level of light that is critical for growth and photosynthesis of this species. Photosynthetic performance, chlorophyll a and b concentrations, organic and carbon contents, percentage cover, and morphology were estimated in E. canadensis from middle of Songkhla lagoon under 4 treatments (25, 50, 75, and 100% of natural light) for 10 weeks. The results show that there were no differences in growth and photosynthesis among the treatments, but low light led to changes in chlorophyll concentration, Fv/Fm, and Ik, suggesting adaptations to a low light regime. This study provides an understanding of physiological tolerance and response to shading and shows how species of aquatic macrophytes respond to future climatic and anthropogenic changes, thereby supporting development of sustainable lagoon management plans. [ABSTRACT FROM AUTHOR]

Macrophytes play an important role in maintaining high physical and biological diversity in freshwater ecosystems. However, during the past several centuries since the industrial revolution, human activities and climate change have caused significant changes in the structure and function of aquatic environments, for example via increased temperature or high sedimentation that reduces light penetration. This study investigated the combined effects of elevated temperature and low light on growth and photosynthetic performance of submerged macrophytes Ceratophyllum demersum and Elodea canadensis and identified temperature and light thresholdsfor these species. Photosynthetic performance, chlorophyll a and b concentrations, organic and carbon contents, and growth rates were estimated in these two dominant macrophytes sampled from the middle of Songkhla lagoon, subjected to 9 treatments (3 light intensities and 3 temperatures) for 9 weeks. The results show that photosynthetic performance according to the indicators EQY, α and rETRmax was inhibited by low light in both species. C. demersum was more tolerant to temperature and light stresses. This study provides an understanding of physiological tolerance and response to light and temperature stresses, and improves the understanding of how aquatic macrophytes respond to future climatic and anthropogenic changes, supporting the development of sustainable lagoon management plans. [ABSTRACT FROM AUTHOR]

Increasing levels of greenhouse gases lead to ocean warming, which affects a range of marine organisms. Corals live in a narrow temperature range and become stressed when the temperatures change. Bleaching occurs when the temperature exceeds the coral’s threshold, and can be severe when this is combined with other stressors such as light. In order to understand how temperature and light affect corals in their physiological responses and photosynthetic performance, Pocillopora acuta from Maiton Island (MT) and Panwa Cape (PW), representing different environments, were investigated. The results show that light and temperature had by regime different effects on Symbiodiniaceae photosynthesis and the coral growth rate. There was a synergistic effect of elevated temperature and light on photosynthesis, as observed in the photochemical efficiency and pigment contents, suggesting photo-damage. A higher growth rate in Panwa corals was observed in control, and while elevated temperature reduced coral growth. Elevated temperature affected the Panwa coral less, suggesting that corals from this regime might be able to recover when the temperature returns to normal. This information is important for predicting the coral responses to elevated temperature especially in the summer, as regards the possibility of coral bleaching.

Land‐based coral culture is of increasing interest for conservation and educational display. Shallow water corals generate most of their energy from photosynthesis, and light is a critical abiotic factor in their husbandry. We compared growth, calcification, and photobiology in the coral Acropora cervicornis between natural and artificial (light‐emitting diode; LED) light to better understand the impact of light source on coral performance. One tank of a greenhouse recirculating system at The Florida Aquarium's Center for Conservation was used to culture replicate coral colonies. Half of the tank and corals were covered to block sunlight and illuminated with a commercial reef aquarium LED fixture, while the other half was exposed to natural sunlight. Treatments were matched in terms of maximum photosynthetically active radiation and spectral measurements characterized both light regimes. Coral growth and calcification were tracked over a period of 19 weeks by repeated measurements of total linear extension (TLE) and buoyant weight. For the first 5 weeks, photosynthetic yield was measured weekly using a pulse‐amplitude‐modulated fluorometer. Calcification was significantly higher under LED lighting relative to natural light, but TLE did not differ. Photobiology data suggest that corals in both treatments were acclimated to the same light level, but photosynthetic efficiency was ultimately greater in the natural light treatment. More consistent light delivery and different spectral composition under LED treatment conditions may explain the incongruity between calcification and photosynthetic efficiency. This experiment informs husbandry of shallow‐water scleractinian corals maintained in both natural sunlight and enclosed structures. Highlights: Light source affected calcification but not linear growth in a branching Caribbean coral.Photobiology data suggest that corals were acclimated to the same light level, but natural light yielded higher photosynthetic efficiency. [ABSTRACT FROM AUTHOR]

The common green alga Trentepohlia sp. was found growing as a biofilm on galvanised iron lamp posts where it was exposed to high zinc levels and periodic desiccation. Its sole water sources were rainfall and dewfall. Photosynthesis studies using PAM techniques showed that the alga was a shade-adapted species with a very low optimum irradiance (Eopt) of about 90 μmol photons m−2 s−1, and ETRmax about 80 μmol e− g−1 chlorophyll-a s−1. But, within minutes, it recovered from desiccation (homiochlorophyllous). The alga has a high chlorophyll-b/a ratio (0.470 ± 0.016) and conspicuous chlorophyll-b absorption in vivo, but no measureable Zn-chlorophyll derivatives were found spectrophotometrically. Mannitol experiments using up to 1.5 Osmol kg−1 showed that photosynthesis in Trentepohlia sp. was highly resistant to water stress. Photosynthesis of Trentepohlia sp. was unaffected by pH even though the abundance of CO2 in the experimental medium dropped from 477 mmol m−3 at pH 5 to less than 1 mmol m−3 at pH 9. Thus, Trentepohlia sp. can use both CO2 and HCO3− as inorganic carbon sources. Acid pH (pH 5) did not increase toxicity of Zn. Trentepohlia sp. was resistant to added Zn with little effect on photosynthetic parameters even at 30 mol m−3 Zn. [ABSTRACT FROM AUTHOR]

Microalgal biofilms are increasingly attracting attention as a cultivation platform for different biotechnological purposes. The initial adhesion of algae to a surface, one of the key factors for the formation of a biofilm, was analyzed by coupling image analysis techniques and mathematical modeling. Two isolated microalgae, Chlorella vulgaris ACUF_809 and Chlorella sp. ACUF_802, were identified by molecular techniques. Their health condition and biomass growth were measured using pulse amplitude modulated (PAM) fluorometry; the carrier colonization was studied by imaging analysis (Weka Segmentation) and measuring the green tones of the biofilm through CIELAB colorimetry. Structural features and biofilm vertical distribution were determined by multichannel confocal laser scanning microscopy (CLSM), and some parameters were aligned to the Gompertz model. Chlorella vulgaris ACUF_809 showed good adaptation to form biofilm on cotton fabric measured as high biomass growth reflected in the high F0 (0.42) and biofilm colonization through the CIELAB colorimetry (a*− 9.3), coverage area 32.3%, and average biofilm thickness (106.37 ± 47 μm). This work demonstrated the feasibility of C. vulgaris ACUF_809 and Chlorella sp. ACUF_802 biofilm formation on cotton fabric which potentially provides an alternative for cultivating and producing microalgae biomass. [ABSTRACT FROM AUTHOR]

Duckweeds (Lemnaceae species) are extensively used models in ecotoxicology, and chlorophyll fluorescence imaging offers a sensitive and high throughput platform for phytotoxicity assays with these tiny plants. However, the vast number of potentially applicable chlorophyll fluorescence-based test endpoints makes comparison and generalization of results hard among different studies. The present study aimed to jointly measure and compare the sensitivity of various chlorophyll fluorescence parameters in Spirodela polyrhiza (giant duckweed) plants exposed to nickel, chromate (hexavalent chromium) and sodium chloride for 72 h, respectively. The photochemistry of Photosystem II in both dark- and light-adapted states of plants was assessed via in vivo chlorophyll fluorescence imaging method. Our results indicated that the studied parameters responded with very divergent sensitivity, highlighting the importance of parallelly assessing several chlorophyll fluorescence parameters. Generally, the light-adapted parameters were more sensitive than the dark-adapted ones. Thus, the former ones might be the preferred endpoints in phytotoxicity assays. Fv/Fm, i.e., the most extensively reported parameter literature-wise, proved to be the least sensitive endpoint; therefore, future studies might also consider reporting Fv/Fo, as its more responsive analogue. The tested toxicants induced different trends in the basic chlorophyll fluorescence parameters and, at least partly, in relative proportions of different quenching processes, suggesting that a basic distinction of water pollutants with different modes of action might be achievable by this method. We found definite hormetic patterns in responses to several endpoints. Hormesis occurred in the concentration ranges where the applied toxicants resulted in strong growth inhibition in longer-term exposures of the same duckweed clone in previous studies. These findings indicate that changes in the photochemical efficiency of plants do not necessarily go hand in hand with growth responses, and care should be taken when one exclusively interprets chlorophyll fluorescence-based endpoints as general proxies for phytotoxic effects.

Staghorn corals represent dominant reef-builders in lagoons and back reefs in Guam. These habitats experience peak seawater temperatures close to 36°C during the hottest months of the year which causes increasingly frequent bleaching episodes that have led to major staghorn coral declines. To study the photo-physiological response of staghorn corals to bleaching conditions, pulse amplitude modulated (PAM) fluorometry was used to record signatures of chlorophyll fluorescence in Acropora cf. pulchra. Fragments of A. cf. pulchra were subjected to a week-long heat treatment some 2–3°C above average ambient seawater temperatures of 30°C; a four-week long recovery period at ambient temperatures followed treatment. While heat-treated coral fragments exposed to full sun responded with immediate and lasting declines in photosynthetic efficiency, shading of coral fragments largely mitigated the effects of elevated seawater temperatures. Of particular concern to reef management efforts is the finding that the strongest effects of heat stress were observed during the recovery period following the initial heat stress. Indeed, it took three times as long as the initial stress event lasted for photosynthesis to return to baseline levels. This lengthy recovery period appears to be driven by photodamage, likely requiring time-consuming protein synthesis-dependent repair of damaged photosystems and replacement of damaged zooxanthellae. These results highlight the importance of developing and implementing coral bleaching intervention efforts well beyond the end of bleaching conditions to facilitate recovery of affected reefs. [ABSTRACT FROM AUTHOR]

The physiological plasticity of five cyanobacteria microbial mats from an extreme high temperature intertidal environment (SW Iceland) was analysed both daily and seasonally. Daily cycles under in situ natural conditions were monitored from June to October using pulse-amplitude modulated (PAM) fluorometry and pigment composition in order to study the photosynthetic performance of these microbial mats in relation to environmental fluctuations linked to irradiance and temperature. In vitro temperature and salinity experiments of photosynthetic responses were also conducted. A total of 10 taxa were identified, the most abundant species being Cyanobacterium sp. and Geitlerinema sp. The microbial mats showed a remarkable photosynthetic adaptation to daily and seasonal changes in temperature and solar radiation. For all microbial mats, rETRmax values decreased from June to October, while Fv/Fm remained constant in terms of absolute values. Although high irradiances during June and July affected photosynthesis through photoinhibition, recovery was observed under high temperatures (between 40–50°C), which supports the hypothesis that temperature is a determining factor in the photosynthetic performance of these cyanobacterial mats. Our results showed a significant increase in the Chla-b and phycobiliproteins content from June to October, as well as a significant decrease in total carotenoids content. [ABSTRACT FROM AUTHOR]

Many crops require not only leaf photosynthesis for their seed development but also the photochemical reactions that occur in the seeds. The purpose of this work was a comparative analysis of light transmittance and photochemical activity in the leaves of Pisum sativum L. and its pericarp, seed coat, and cotyledons at the early, middle, and late maturation stages. The spectral composition of light was measured using a spectroradiometer in the range of 390-760 nm. We assessed the light transmittance of plant tissues by placing the plant tissue between the light source and the spectroradiometer's sensor. PAM fluorometry was used to quantify the photochemical activity in plant tissues: this technique is handy for evaluating the efficiency of converting light energy into chemical energy through the analysis of the kinetics of chlorophyll fluorescence excitation and quenching. On average, a photochemically active green leaf of pea transmitted 15 % of solar radiation in the 390-760 nm, blue light was delayed entirely, and the transmitted red light never exceeded 5 %. Photochemically active radiation passing through the pericarp and coat and reaching the cotyledons at the early and middle seed maturation stages manifested a high proportion of green and far-red light; there was no blue light, and the percentage of red light was about 2 %. However, the cotyledons were photochemically active regardless of low irradiance and spectral ranges untypical of leaf photosynthesis. At the early and middle maturation stages, the maximum quantum yield of photosystem II (Fv/Fm) averaged 0.5 at the periphery of cotyledons and 0.3 at their center. Since the intensity of embryonic photochemical reactions significantly affects the efficiency of reserve nutrient accumulation, this parameter is a promising marker in pea breeding for seeds with improved nutritional qualities., Competing Interests: The authors declare no conflict of interest., (Copyright © AUTHORS.)

Posidonia oceanica (L.) Delile meadows are recognized to be one of the most productive ecosystems of the Mediterranean basin. Due to the impacts of human activities in coastal areas, seagrasses are experiencing a critical decline. In this context, the understanding of the dynamics of production and photosynthesis in response to the environmental factors is essential to address efficient conservation strategies that limit this trend and to assess the ecological status of marine ecosystems. Pulse Amplitude Modulated (PAM) fluorometry has been widely implemented to assess seagrass health and productivity. Here we analyzed the photosynthetic dynamics of P. oceanica according to its bathymetric distribution and daily light availability along a depth gradient to be used as baseline for monitoring purposes on the health status of the seagrass meadows in the Northern Tyrrhenian Sea. Moreover, to investigate the effects of the environmental factors on the health status of P. oceanica within the study area through a multidisciplinary approach, the models contained in the Civitavecchia Coastal Environmental Monitoring System were used. In this study, significant photo-physiological changes have been observed among the investigated meadows. Moreover, the integration of physiological and hydrodynamic information allowed the description of how P. oceanica modulates its photosynthetic capacity at different environmental conditions.

Plants naturally contain high levels of the stress-responsive fluorophore chlorophyll. Chlorophyll fluorescence imaging (CFI) is a powerful tool to measure photosynthetic efficiency in plants and provides the ability to detect damage from a range of biotic and abiotic stresses before visible symptoms occur. However, most CFI systems are complex, expensive systems that use pulse amplitude modulation (PAM) fluorometry. Here, we test a simple CFI system, that does not require PAM fluorometry, but instead simply images fluorescence emitted by plants. We used this technique to visualize stress induced by the photosystem II-inhibitory herbicide atrazine. After applying atrazine as a soil drench, CFI and color images were taken at 15-minute intervals, alongside measurements from a PAM fluorometer and a leaf reflectometer. Pixel intensity of the CFI images was negatively correlated with the quantum yield of photosystem II (ΦPSII) (p < 0.0001) and positively correlated with the measured reflectance in the spectral region of chlorophyll fluorescence emissions (p < 0.0001). A fluorescence-based stress index was developed using the reflectometer measurements based on wavelengths with the highest (741.2 nm) and lowest variability (548.9 nm) in response to atrazine damage. This index was correlated with ΦPSII (p < 0.0001). Low-cost CFI imaging can detect herbicide-induced stress (and likely other stressors) before there is visual damage.

Microalgal toxicity tests using integrative endpoints as algal growth are regularly required to analyse the toxicity of potentially hazardous substances in the aquatic environment. However, these do not provide mechanistic information on the toxic mode of action by which contaminants may affect algae. Bottled waters can be used as a substitute for culturing media and should not impose any stress to the cultured organisms. However, certain chemical components can interfere with specific cell targets which are not revealed by general toxicity assays. The present study investigated the sensitivity of flow cytometry (FCM) to analyse sub-lethal effects of different bottled waters to the freshwater microalgae Raphidocelis subcapitata. Several endpoints were analysed including growth rate, natural pigments content, cell size, complexity, viability and cycle, Reactive Oxygen Species (ROS) formation, mitochondrial membrane potential and Lipid Peroxidation (LPO). Additionally, photosystem II (PSII) performance was analysed by PAM fluorometry, to provide further information on the absorption, distribution and use of energy in photosynthesis. Results indicated that the most sensitive endpoints were the oxidative stress related endpoints ROS formation and LPO, pigment content, morphological endpoints as cell size, complexity and cycle, with growth rate being one of the least sensitive. Although being essential macronutrients for algal growth, the chemical elements Ca, Na, Mg, and NH 4 were identified as being primarily responsible for the observed toxicological effects to exposed algae. The applied methodology proved to be of high throughput, simultaneously assembling information on morphological, biochemical, and physiological status of algal cells. FCM also showed potential to reveal mechanistic information on the toxic mode of action of the bottled waters before any effects on algal growth was observed. The used approach demonstrated its potential for being integrated into future microalgal toxicity bioassays for testing chemicals to improve the hazard information obtained from currently approved internationally accepted test guidelines. Unlabelled Image • Sub-lethal toxicity of bottled waters to Raphidocelis subcapitata • Reactive oxygen species formation, lipid peroxidation, effects in pigments, cell size, complexity and cell cycle observed • Ca, Na, Mg, and NH 4 primarily responsible for the observed effects • The methodological approach effectively revealed the observed mechanistic effects. [ABSTRACT FROM AUTHOR]

Stochastic upwelling of seawater in the Baltic Sea from the deep, anoxic bottoms may bring low-pH water rich in CO2 close to the surface. Such events may become more frequent with climate change and ongoing ocean acidification (OA). Photoautotrophs, such as macroalgae, which are important foundation species, have been proposed to benefit from increased carbon availability due to reduced energetic cost in carbon acquisition. However, the exact effects of CO2 fertilization may depend on the ambient light environment, as photosynthesis rates depend on available irradiance. In this experimental study, interacting effects of CO2 addition and irradiance on the habitat-forming macroalga Fucus vesiculosus were investigated during two seasons – winter and summer – in the northern Baltic Sea. Growth rates remained unaffected by CO2 or irradiance during both seasons, suggesting that direct effects of elevated CO2 on mature F. vesiculosus are small. Increases in CO2 affected algal elemental ratios by increasing carbon and decreasing nitrogen content, with resulting changes in the C:N ratio, but only in winter. In summer, chlorophyll a content increased under low irradiance. Increases in CO2 caused a decline in light-harvesting efficiency (decrease in Fv/Fm and α) under high irradiance in summer, and conversely increased α under low irradiance. High irradiance caused increases in the maximum relative electron transport rate (rETRmax) in summer, but not in winter. Differences between winter and summer indicate that F. vesiculosus responses to CO2 and irradiance are season-specific. Increases in carbon content during winter could indicate slightly positive effects of CO2 addition in the long run if the extra carbon gained may be capitalized in growth. The results of this study suggest that increases in CO2, either through upwelling or OA, may have positive effects on F. vesiculosus, but these effects are probably small. [ABSTRACT FROM AUTHOR]

Changes in photosynthetic efficiency of Photosystem II can be used as an early stress indicator in phototrophs. In this study, chlorophyll fluorescence, measured by a Pulse-Amplitude Modulated Fluorometer (PAM), was used to determine the photosynthetic performance of tropical, temperate, Antarctic and Arctic Chlorella in response to short-term acute ultraviolet radiation (UVR) stress, with measurements of maximum quantum yield (Fv/Fm), photosynthetic efficiency (α), maximum electron transport rate (rETRm) and photoadaptive index (E k). Three light treatments were conducted over a continuous, five-hour duration: (i) control subjected only to photosynthetic active radiation (PAR), (ii) PAR + UVA (UVA) and (iii) PAR + UVA + UVB (UVR). Tropical Chlorella showed better adaptive ability to UVA stress compared to strains from temperate and polar regions. UVB stress caused significant photosynthetic dysfunction in all samples, with polar strains showing a lower inhibition (about 40%) compared to the tropical strain (about 98%). Photosynthetic responses in Chlorella towards UVR are possibly origin dependent. DNA mutation induced by both UVA and UVR treatments was revealed by Random Amplified Polymorphic DNA (RAPD) analysis. Out of sixty RAPD primers tested, two primers: S33 (polymorphism degree 44.83%) and S90 (polymorphism degree 38.71%) were chosen as potential primers to conduct genomic study of UV stress in microalgae. [ABSTRACT FROM AUTHOR]

Abstract Microalgae have been widely used in ecotoxicological studies in order to evaluate the impacts of heavy metals in aquatic ecosystems. However, there are few studies that analyze the effects of metals in an integrative way on photosynthetic apparatus of freshwater microalgae in the generation of reactive oxygen species (ROS) and biochemical composition. Therefore, this study aimed to assess cadmium (Cd) and lead (Pb) toxicity using synchronously physiological and biochemical endpoints, specially detecting lipidic classes for the very first time during Cd and Pb-exposure to Raphidocelis subcapitata. Here we show that analyzing the algae growth, the IC50–72 h for Cd was 0.04 µM and for Pb was 0.78 µM. In general, the Cd affected the biochemical parameters more, leading to an increase in total lipid content (7.2-fold), total carbohydrates (3.5-fold) and ROS production (3.7-fold). The higher production of lipids and carbohydrates during Cd-exposure probably acted as a defense mechanism, helping to reduce the extent of damage caused by the metal in the photosynthetic apparatus. For Pb, the physiological parameters were more sensitive, which resulted in changes of chlorophyll a synthesis and a reduction of both efficiency of oxygen-evolving complex and quantum yields. Besides that, we observed changes in the lipid class composition during Cd and Pb-exposure, suggesting these analyses as great biomarkers to assess metal toxicity mechanisms in ecological risk assessments. Thereby, here we demonstrate the importance of using multiple endpoints in ecotoxicological studies in order to obtain a better understanding of the mechanisms of metal toxicity to R. subcapitata. Highlights • IC50–72 h for growth inhibition were 0.04 µM to Cd and 0.78 µM to Pb. • For Cd, ROS production was the main mode of action. • For Pb, damage to photosynthetic apparatus was the main toxicity mechanism. • Lipidic classes were great biomarkers to assess Cd and Pb toxicity mechanisms. • Pb increased more FFA, ALC and HC levels. Cd increased more FFA, ST and TAG levels. [ABSTRACT FROM AUTHOR]