Patrones estacionales de fotoaclimatación en el alga intermareal, Cystoseira tamariscifolia (Ochrophyta)

Cystoseira tamariscifolia thalli collected from rocky shores and rockpools in winter and summer in Southern Spain were incubated for 7 days in UV transparent cylindrical vessels under outdoor conditions. Photosynthetic activity estimated as in vivo chlorophyll α fluorescence of photosystem II, photosynthetic pigments, antioxidant activity (DPPH assay), phenolic compounds and total internal C and N contents were determined after short-term (3 d) and mid-term (7 d) periods. Maximum quantum yield of PSII (Fv/Fm) was significantly higher in field-collected algae and after 7 d incubation in winter than in summer. In rocky shores and rockpools thalli, maximum electron transport rate (ETRmax) and photosynthetic efficiency (αETR) were much higher in summer than in winter. ETR of outdoor-grown thalli (in situ ETR) showed a daily pattern, with a decrease at noon in both winter and summer (3rd and 7th days). We found much higher antioxidant activity in thalli collected in summer than in winter. However, the concentration of internal UV screen substances (polyphenols) was higher in winter than in summer, whereas the release of phenolic compounds was lower. The highest capacity of acclimation in C. tamariscifolia found in summer and RS with emersion periods was explained by the highest dynamic photoinhibition, energy dissipation (non-photochemical quenching) and antioxidant activity (EC50).Talos de Cystoseira tamariscifolia recolectados en pozas y plataformas rocosas intermareales (Sur de España) en invierno y en verano se incubaron bajo radiación solar durante 7 días en recipientes cilíndricos de metacrilato transparentes a la radiación UV. Se estimó la actividad fotosintética a través de la fluorescencia de la clorofila α asociada al fotosistema II, el contenido de pigmentos fotosintéticos y compuestos fenólicos, actividad antioxidante y el contenido total en C y N internos tras 3 y 7 días de incubación. Los valores iniciales del rendimiento cuántico máximo (Fv/Fm) fueron significativamente mayores en algas recolectadas en invierno que en verano mientras que la tasa de transporte electrónico máximo (ETRmax) y la eficiencia fotosintética fueron mayores en verano que en invierno en ambas zonas. Por otra parte, la tasa de transporte electrónico determinada bajo radiación solar presentó un patrón diario, con una disminución a mediodía, tanto en invierno como en los períodos de verano. La actividad antioxidante fue mayor en algas recogidas en verano; sin embargo, la concentración interna de compuestos fenólicos fue mayor en invierno que en verano, mientras que en la tasa de excreción se observó lo contrario. La alta capacidad de aclimatación en C. tamariscifolia en algas sometidas a emersión en las plataformas rocosas en verano se explica por su alta fotoinhibición dinámica, su capacidad de disipación de energía (amortiguamiento no fotoquímico, NPQ) y su actividad antioxidante (EC50)

Daily changes on seasonal ecophysiological responses of the intertidal brown macroalga Lessonia spicata: Implications of climate change

Global climate change is expected to have detrimental effects on coastal ecosystems, with impacts observable at the local and regional levels, depending on factors such as light, temperature, and nutrients. Shifts in dominance between primary producers that can capitalize on carbon availability for photosynthesis will have knock-on effects on marine ecosystems, affecting their ecophysiological responses and biological processes. Here, we study the ecophysiological vulnerability, photoacclimation capacity, and tolerance responses as ecophysiological responses of the intertidal kelp Lessonia spicata (Phaeophyceae, Laminariales) during a year through different seasons (autumn, winter, spring, and summer) in the Pacific Ocean (central Chile). Six different daily cycle experiments were carried out within each season. A battery of different biochemical assays associated with antioxidant responses and in-vivo chlorophyll a fluorescence parameter showed that during spring and summer, there was an increase in photosynthetic capacity in the macroalgae, although their responses varied depending on light and nutrient availability in the course of the year. Lessonia spicata showed maximal photosynthesis and a similar photoinhibition pattern in summer compared to the other seasons, and the contents of nitrate and phosphorous in seawater were less in winter. Thus, high irradiance during spring and summer displayed a higher maximal electron transport rate (ETRmax), irradiance of saturation (Ek), non-photochemical quenching (NPQmax), nitrogen and carbon contents, and photoprotector compound levels. Antioxidant activity increased also in summer, the seasonal period with the highest oxidative stress conditions, i.e., the highest level of hydrogen peroxide (H2O2). In contrast, under low irradiance, i.e., wintertime conditions, L. spicata demonstrated lower concentrations of the photosynthetic pigments such as chlorophyll a and carotenoids. Our study suggests that macroalgae that are subjected to increased irradiance and water temperature under lower nutrient availability mediated by seasonal changes (expected to worsen under climate change) respond with higher values of productivity, pigment contents, and photoprotective compounds. Thus, our findings strengthen the available evidence to predict that algae in the order Laminariales, specifically L. spicata (kelp), could better proliferate, with lower vulnerability and greater acclimation, than other marine species subject to future expected conditions associated with climate change.Financial and logistical support was granted by the project of Fondo Nacional de Desarrollo Científico y Tecnológico, Chile through grant Project FONDECYT, Chile N° 11180197, ANID, Chile - provided to Paula Celis - Plá

MAPK Pathway under Chronic Copper Excess in Green Macroalgae (Chlorophyta): Involvement in the Regulation of Detoxification Mechanisms

Following the physiological complementary/parallel Celis-Plá et al., by inhibiting extracellular signal regulated kinases (ERK), c-Jun N-terminal kinases (JNK), and cytokinin specific binding protein (p38), we assessed the role of the mitogen-activated protein kinases (MAPK) pathway in detoxification responses mediated by chronic copper (10 µM) in U. compressa. Parameters were taken at 6, 24, and 48 h, and 6 days (d). H2O2 and lipid peroxidation under copper and inhibition of ERK, JNK, or p38 alone increased but recovered by the sixth day. By blocking two or more MAPKs under copper, H2O2 and lipid peroxidation decayed even below controls. Inhibition of more than one MAPK (at 6 d) caused a decrease in total glutathione (reduced glutathione (GSH) + oxidised glutathione (GSSG)) and ascorbate (reduced ascorbate (ASC) + dehydroascorbate (DHA)), although in the latter it did not occur when the whole MAPK was blocked. Catalase (CAT), superoxide dismutase (SOD), thioredoxin (TRX) ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione synthase (GS), were downregulated when blocking more than one MAPK pathway. When one MAPK pathway was blocked under copper, a recovery and even enhancement of detoxification mechanisms was observed, likely due to crosstalk within the MAPKs and/or other signalling processes. In contrast, when more than one MAPK pathway were blocked under copper, impairment of detoxification defences occurred, demonstrating that MAPKs were key signalling mechanisms for detoxification in macroalgae.</jats:p

Photoprotective responses of three intertidal Antarctic macroalgae to short-term temperature stress

The Antarctic Peninsula is experiencing one of the highest warming rates globally. In polar regions, macroalgae thrive under extreme environmental conditions, which could worsen because of future climate change scenarios, including increased ultraviolet exposure, extremely low light availability, and fluctuating temperatures, particularly in the intertidal zones. To investigate the potential role of photoprotective and antioxidant mechanisms in response to future increases in sea surface temperatures caused by climate change, we conducted laboratory experiments using three intertidal macroalgae model species: Adenocystis utricularis (Ochrophyta, Phaeophyceae), Pyropia endiviifolia (Rhodophyta, Bangiophyceae), and Monostroma hariotii (Chlorophyta, Ulvophyceae). These algae were collected in Punta Artigas (King George Island, Antarctica) and acclimated at 2°C for 48 h. They were then assessed in laboratory experiments for up to 5 days under two treatments: (1) control conditions at 2°C and (2) elevated tem.perature conditions at 8°C, representing the most negative increment in SSTs estimated by the end of the 21st century. Carbon, nitrogen, pigments (chlorophylls and carotenoids), mycosporine-like amino acids (MAAs), and phenolic compounds were quantified after 3 and 5 days of exposure. For M. hariotii, elevated temperatures led to an increase in the C/N ratio, total antioxidant capacity, and levels of nitrogen, total carotenoids, chlorophyll-a, pigments (chlorophyll-b and violaxanthin), and phenolic compounds. For A. utricularis, elevated temperatures led to elevated C/N ratio and levels of chlorophyll-a and carotenoids (fucoxanthin and β-carotene). For P. endiviifolia, elevated temperatures resulted in elevated levels of carotenoids (lutein and β-carotene), phenolic compounds, and MAAs (porphyra-334, shinorine, and palythine). Thus, our study suggests that increasing water temperatures due to global warming can enhance the photoprotective abilities of three Antarctic intertidal macroalgae (M. hariotii, A. utricularis, and P. endiviifolia), with each species showing specific responses.Financial and logistical support were granted by the Projects INACH N° RG_10_18 and RT_09_16 granted to PC-P and CS, respectively

Desalination effects on macroalgae (part b): Transplantation experiments at brine-impacted sites with Dictyota spp. from the Pacific Ocean and Mediterranean Sea

Desalination residual brines are mostly discharged to marine environments, which can produce osmotic stress on sensitive benthic organisms. In this investigation, we performed transplantation experiments nearby desalination plants using two brown macroalgae species from a cosmopolitan genus: Dictyota kunthii (Chile) and Dictyota dichotoma (Spain). Parameters related to photosynthetic activity and oxidative stress were evaluated at 3 and 7 days for D. kunthii, and 3 and 6 days for D. dichotoma; each at 2 different impacted sites and 1 control. We observed that brine exposition at both impacted sites in Chile generated a marked stress response on D. kunthii, reflected in a decrease of primary productivity (ETRmax), light requirement (EkETR), and an excessive thermal dissipation (NPQmax), especially at 7 days. In D. dichotoma, similar impaired photosynthetic activity was recorded but only at the highest brine influence site during day 3. Regarding oxidative stress, both species displayed high levels of H2O2 when exposed to brine-influenced sites. Although in D. kunthii H2O2 content together with lipid peroxidation was higher after 3 days, these returned to baseline values towards day 7; instead, D. dichotoma H2O2 levels increased only at day 6. This easy and practical approach has proven to provide valuable data to address potential impacts of brine discharges at global scale coastal ecosystems.We gratefully thank financial support to ANID FONDECYT Postdoctoral fellowship #3180394, European Commission Marie Skłodowska-Curie Actions #888415, and ANID INES I+D # INID210013. Financial support for mobility granted from SEGIB Scholarship and Fundación Carolina of Spain to PM. Also, we thank TESPOST 04/19 PhD scholarship granted by Universidad de Playa Ancha to PM

Transcriptomic profiles and diagnostic biomarkers in the Mediterranean seagrasses Posidonia oceanica and Cymodocea nodosa reveal mechanistic insights of adaptative strategies upon desalination brine stress

Seawater desalination by reverse osmosis is growing exponentially due to water scarcity. Byproducts of this process (e.g. brines), are generally discharged directly into the coastal ecosystem, causing detrimental effects, on benthic organisms. Understanding the cellular stress response of these organisms (biomarkers), could be crucial for establishing appropriate salinity thresholds for discharged brines. Early stress biomarkers can serve as valuable tools for monitoring the health status of brine-impacted organisms, enabling the prediction of long-term irreversible damage caused by the desalination industry. In this study, we conducted laboratory-controlled experiments to assess cellular and molecular biomarkers against brine exposure in two salinity-sensitive Mediterranean seagrasses: Posidonia oceanica and Cymodocea nodosa. Treatments involved exposure to 39, 41, and 43 psu, for 6 h and 7 days. Results indicated that photosynthetic performance remained unaffected across all treatments. However, under 43 psu, P. oceanica and C. nodosa exhibited lipid oxidative damage, which occurred earlier in P. oceanica. Additionally, P. oceanica displayed an antioxidant response at higher salinities by accumulating phenolic compounds within 6 h and ascorbate within 7 d; whereas for C. nodosa the predominant antioxidant mechanisms were phenolic compounds accumulation and total radical scavenging activity, which was evident after 7 d of brines exposure. Finally, transcriptomic analyses in P. oceanica exposed to 43 psu for 7 days revealed a poor up-regulation of genes associated with brassinosteroid response and abiotic stress response, while a high down-regulation of genes related to primary metabolism was detected. In C. nodosa, up-regulated genes were involved in DNA repair, cell cycle regulation, and reproduction, while down-regulated genes were mainly associated with photosynthesis and ribosome assembly. Overall, these findings suggest that 43 psu is a critical salinity-damage threshold for both seagrasses; and despite the moderate overexpression of several transcripts that could confer salt tolerance, genes involved in essential biological processes were severely downregulated.FRR was financed by Fondecyt #11220425 grant from ANID, Chile. CAS was financed by project ANID InES I + D 2021 (INID210013) and by Marie Skłodowska-Curie Action (888415). FBM was supported by a grant from Universidad de Alicante (Grant ID: FPUUA98)

MAPK Pathway under Chronic Copper Excess in Green Macroalgae (Chlorophyta): Influence on Metal Exclusion/Extrusion Mechanisms and Photosynthesis

There is currently no information regarding the role that whole mitogen activated protein kinase (MAPK) pathways play in counteracting environmental stress in photosynthetic organisms. To address this gap, we exposed Ulva compressa to chronic levels of copper (10 µM) specific inhibitors of Extracellular Signal Regulated Kinases (ERK), c-Jun N-terminal Kinases (JNK), and Cytokinin Specific Binding Protein (p38) MAPKs alone or in combination. Intracellular copper accumulation and photosynthetic activity (in vivo chlorophyll a fluorescence) were measured after 6 h, 24 h, 48 h, and 6 days of exposure. By day 6, when one (except JNK) or more of the MAPK pathways were inhibited under copper stress, there was a decrease in copper accumulation compared with algae exposed to copper alone. When at least two MAPKs were blocked, there was a decrease in photosynthetic activity expressed in lower productivity (ETRmax), efficiency (αETR), and saturation of irradiance (EkETR), accompanied by higher non-photochemical quenching (NPQmax), compared to both the control and copper-only treatments. In terms of accumulation, once the MAPK pathways were partially or completely blocked under copper, there was crosstalk between these and other signaling mechanisms to enhance metal extrusion/exclusion from cells. Crosstalk occurred among MAPK pathways to maintain photosynthesis homeostasis, demonstrating the importance of the signaling pathways for physiological performance. This study is complemented by a parallel/complementary article Rodríguez-Rojas et al. on the role of MAPKs in copper-detoxification.</jats:p

Seawater carbonate chemistry and growth rate, primary production of Cystoseira tamariscifolia (Phaeophyceae) in laboratory experiment

Ocean acidification increases the amount of dissolved inorganic carbon (DIC) available in seawater which can benefit photosynthesis in those algae that are currently carbon limited, leading to shifts in the structure and function of seaweed communities. Recent studies have shown that ocean acidification-driven shifts in seaweed community dominance will depend on interactions with other factors such as light and nutrients. The study of interactive effects of ocean acidification and warming can help elucidate the likely effects of climate change on marine primary producers. In this study, we investigated the ecophysiological responses of Cystoseira tamariscifolia (Hudson) Papenfuss. This large brown macroalga plays an important structural role in coastal Mediterranean communities. Algae were collected from both oligotrophic and ultraoligotrophic waters in southern Spain. They were then incubated in tanks at ambient (ca. 400-500 ppm) and high CO2 (ca. 1200-1300 ppm), and at 20 °C (ambient temperature) and 24 °C (ambient temperature +4 °C). Increased CO2 levels benefited the algae from both origins. Biomass increased in elevated CO2 treatments and was similar in algae from both origins. The maximal electron transport rate (ETRmax), used to estimate photosynthetic capacity, increased in ambient temperature/high CO2 treatments. The highest polyphenol content and antioxidant activity were observed in ambient temperature/high CO2 conditions in algae from both origins; phenol content was higher in algae from ultraoligotrophic waters (1.5-3.0%) than that from oligotrophic waters (1.0-2.2%). Our study shows that ongoing ocean acidification can be expected to increase algal productivity (ETRmax), boost antioxidant activity (EC50), and increase production of photoprotective phenols. Cystoseira tamariscifolia collected from oligotrophic and ultraoligotrophic waters were able to benefit from increases in DIC at ambient temperatures. Warming, not acidification, may be the key stressor for this habitat as CO2 levels continue to rise