Role of protective and repair mechanisms in the inhibition of photosynthesis in marine macroalgae

The differing responses of central carbon cycle metabolism in male and female Sargassum thunbergii to ultraviolet-B radiation

The enhancement of ultraviolet-B radiation (UV-B) radiation reaching the Earth's surface due to ozone layer depletion is an important topic. Macroalgal species growing in the intertidal zone are often directly exposed to UV-B radiation periodically as the tide changes. In order to better understand the response of macroalgae to UV-B stressed condition, we studied the dominant dioecious intertidal macroalgae Sargassum thunbergii. After consecutive UV-B radiation treatments, we used metabonomics models to analyze and compare the maximum photosynthetic electron transport rate (ETR_max), central carbon cycle metabolism (CCCM) gene expression level, CCCM enzymic activities [pyruvate dehydrogenase and citrate synthase (PDH and CS)], and carbon-based metabolite (including pyruvate, soluble sugar, total amino acid, and lipids) content in male and female S. thunbergii. The results showed that under low and high UV-B radiation, the ETR_max values and six targeted CCCM gene expression levels were significantly higher in males than in females. Under high UV-B radiation, only the CS activity was significantly higher in males than in females. There was no significant difference in PDH activity between males and females. The CCCM models constructed using the metabonomics analysis demonstrate that S. thunbergii males and females exhibit obvious gender differences in their responses to UV-B radiation, providing us with a new understanding of the macroalgal gender differences under UV-B radiation, as past investigations always underestimated their diecious characteristics.

Physiological Responses and Metabonomics Analysis of Male and Female Sargassum thunbergii Macroalgae Exposed to Ultraviolet-B Stress

Ultraviolet-B (UV-B) radiation is a major environmental stress that suppresses or activates defense responses in organisms. UV-B radiation affecting growth and development in intertidal species have been researched for a long time, but a series of unknown knowledge remain in the male and female macroalgae comparison. To compare the different responses of male and female Sargassum thunbergii macroalgae under UV-B radiation, PSII photochemical efficiency determination, metabolomic analysis, and main carbon-based metabolites (including soluble sugar, total amino acid, and lipid) content measuring have been performed in our experiments. Results showed that males have significantly superiority performance in the chlorophyll fluorescence parameters of F _v/F _m, Y(II), and Y(NO) either low or high UV-B radiation treatments. Metabolomics analysis revealed that carbon and nitrogen metabolism pathways in male and female S. thunbergii were significant components responding to enhanced UV-B radiation. Based on measuring, female S. thunbergii lipid content expressed higher than males without any stimulation. Additionally, under low UV-B radiation stimulation, females total amino acid content shown significantly higher than control group and their lipid content also significantly higher than males. Under high UV-B radiation, males soluble sugar, total amino acid, and lipid content significantly varied from females, which meant that enhancing UV-B stress might altered mainly carbon-based metabolites flowing directions. The present study elucidated the potential role of enhanced UV-B radiation in regulating macroalgae physiological responses, metabolites changing, and reflecting differences between male and female S. thunbergii, contributing to understanding of brown-macroalgae diecious adopting mechanisms in defending intertidal UV-B stresses.

Photosynthetic Characteristics of Three Cohabitated Macroalgae in the Daya Bay, and Their Responses to Temperature Rises

Biochemical compositions and photosynthetic characteristics of three naturally cohabitated macroalgae, Ulva fasciata, Sargassum hemiphyllum and Grateloupia livida, were comparably explored in the field conditions in Daya Bay, northern South China Sea, as well as their responses to temperature rise. Chlorophyll a (Chl a) and carotenoids contents of U. fasciata were 1.00 ± 0.15 and 0.57 ± 0.08 mg g^-1 in fresh weight (FW), being about one- and two-fold higher than that of S. hemiphyllum and G. livida; and the carbohydrate content was 20.3 ± 0.07 mg g^-1 FW, being about three- and one-fold higher, respectively. Throughout the day, the maximal photochemical quantum yield (F_V/F_M) of Photosystem II (PS II) of these three macroalgae species decreased from morning to noon, then increased to dusk and kept steady at nighttime. Consistently, the rapid light curve-derived light utilization efficiency (α) and maximum relative electron transfer rate (rETRmax) were lower at noon than that at morning- or night-time. The F_V/F_M of U. fasciata (varying from 0.78 to 0.32) was 38% higher than that of G. livida throughout the day, and that of S. hemiphyllum was intermediate. The superoxide dismutase (SOD) and catalase (CAT) activities in U. fasciata were lower than that in S. hemiphyllum and G. livida. Moreover, the rises in temperature species-specifically mediated the damage (k) caused by stressful high light and the corresponding repair (r) to photosynthetic apparatus, making the r/k ratio increase with the rising temperature in U. fasciata, unchanged in S. hemiphyllum but decreased in G. livida. Our results indicate that U. fasciata may compete with S. hemiphyllum or G. livida and dominate the macroalgae community under aggravatedly warming future in the Daya Bay.

Increased CO2 Relevant to Future Ocean Acidification Alleviates the Sensitivity of a Red Macroalgae to Solar Ultraviolet Irradiance by Modulating the Synergy Between Photosystems II and I

While intertidal macroalgae are exposed to drastic changes in solar photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) during a diel cycle, and to ocean acidification (OA) associated with increasing CO₂ levels, little is known about their photosynthetic performance under the combined influences of these drivers. In this work, we examined the photoprotective strategies controlling electron flow through photosystems II (PSII) and photosystem I (PSI) in response to solar radiation with or without UVR and an elevated CO₂ concentration in the intertidal, commercially important, red macroalgae Pyropia (previously Porphyra) yezoensis. By using chlorophyll fluorescence techniques, we found that high levels of PAR alone induced photoinhibition of the inter-photosystem electron transport carriers, as evidenced by the increase of chlorophyll fluorescence in both the J- and I-steps of Kautsky curves. In the presence of UVR, photoinduced inhibition was mainly identified in the O₂-evolving complex (OEC) and PSII, as evidenced by a significant increase in the variable fluorescence at the K-step (F _k) of Kautsky curves relative to the amplitude of F _J-F _o (W_k) and a decrease of the maximum quantum yield of PSII (F _v/F _m). Such inhibition appeared to ameliorate the function of downstream electron acceptors, protecting PSI from over-reduction. In turn, the stable PSI activity increased the efficiency of cyclic electron transport (CET) around PSI, dissipating excess energy and supplying ATP for CO₂ assimilation. When the algal thalli were grown under increased CO₂ and OA conditions, the CET activity became further enhanced, which maintained the OEC stability and thus markedly alleviating the UVR-induced photoinhibition. In conclusion, the well-established coordination between PSII and PSI endows P. yezoensis with a highly efficient photochemical performance in response to UVR, especially under the scenario of future increased CO₂ levels and OA.

Effects of phosphorus availability and phosphorus utilization behavior of Microcystis aeruginosa on its adaptation capability to ultraviolet radiation

Phosphorus (P) plays a critical role in eutrophication and algal growth; therefore, improving our understanding of the impact of P is essential to control harmful algal blooms. In this study, Microcystis aeruginosa was treated with 5-h ambient irradiation in the medium with different dissolved inorganic P (DIP) concentrations, DIP-free, moderate-DIP, and high-DIP, to explore its growth and other physiological responses. Compared to photosynthetically active radiation (PAR), UV-A (320-400 nm) and UV-B (280-320 nm) radiation had inhibitive effects on the photosynthesis and growth of M. aeruginosa, while high P availability could alleviate or eliminate the negative effects of UV radiation. The photosynthetic parameters had a minimum reduction and quickly recovered after re-inoculation under high-DIP conditions. Confirmed by SEM, photosynthetic pigments, the generation of reactive oxygen species (ROS), superoxide dismutase (SOD) activity and other methods, ambient UV radiation exerted oxidative stresses rather than direct lethal effects on M. aeruginosa. Photosynthetic parameters indicated that algal UV-adaptation processes could include decreasing photo-induced damages and increasing self-repair efficiency. The P acquired by M. aeruginosa cells can have two function, which included alleviating UV-induced negative effects and sustaining algal growth. Consequently, UV-adaptation processes of M. aeruginosa resulted in an elevated demand for DIP, which resulted to increased P uptake rates and cellular P quota under moderate and high-DIP conditions. Therefore, the production of carotenoid and phycocyanin, and SOD activity increased under UV stress, leading to a better adaptation capability of M. aeruginosa and decreased negative effects of UV radiation on its growth. Overall, our findings demonstrated the significant interactive effects of P enrichment and irradiation on typical cyanobacteria, and the strong adaptation capability of M. aeruginosa in the eutrophic UV-radiated waters.

Quantitative and Qualitative HPLC Analysis of Mycosporine-Like Amino Acids Extracted in Distilled Water for Cosmetical Uses in Four Rhodophyta

Mycosporine-like amino acids (MAAs) have gained considerable attention as highly active photoprotective candidates for human sunscreens. However, more studies are necessary to evaluate the extraction efficiencies of these metabolites in cosmetic compatible solvents, as well as, their subsequent HPLC analysis. In the present study, MAA extraction using distilled water and 20% aqueous methanol in four Rhodophyta was investigated. Different re-dissolution solvents and a C8 and C18 columns were tested for the HPLC analysis. Porphyra-334, shinorine, palythine, palythine-serine, asterina-330, and palythinol were identified by HPLC/ESI-MS. The separation of these MAAs were improved employing the C8-column, and using methanol as re-dissolution solvent. Regarding total MAAs concentrations, no differences between the two solvents were found. The highest MAA amounts were observed injecting them directly in the HPLC. According to these results, distilled water could be an excellent extraction solvent for MAAs. Nevertheless, the re-dissolution in pure methanol after dryness would be the best option for the qualitative analysis of the most common MAAs in these red algae. Our results entail important implications regarding the use of red macroalgae as promising candidates as environment-friendly sources of natural sunscreens.

Impacts of diurnal variation of ultraviolet-B and photosynthetically active radiation on phycobiliproteins of the hot-spring cyanobacterium Nostoc sp. strain HKAR-2

The effects of diurnal variation of photosynthetically active radiation (PAR; 400-700 nm) and ultraviolet-B (UV-B; 280-315 nm) radiation on phycobiliproteins (PBPs) and photosynthetic pigments (PP) have been studied in the hot-spring cyanobacterium Nostoc sp. strain HKAR-2. The variations in PBPs and PP were monitored by alternating light and dark under PAR, UV-B, and PAR + UV-B radiations over a period of 25 h. There was a decline in the amount of Chl a and PBPs during light periods of UV-B and PAR + UV-B and an increase during dark periods showing a circadian rhythm by destruction and resynthesis of pigment-protein complex. However, a marked induction in carotenoids was recorded during light periods of the same radiations. Moreover, the ratio of Chl a/PE and Chl a/PC was increased in dark periods showing the resynthesis of bleached Chl a. The wavelength shift in emission fluorescence of PBPs toward shorter wavelengths further indicated the bleaching and destruction of PBPs during light periods. Oxidative damage upon exposure to PAR, UV-B, and PAR + UV-B was alleviated by induction of antioxidative enzymes such as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). The studied cyanobacterium exhibits a significant increase in the activities of SOD, CAT, and APX upon exposure to UV-B and PAR + UV-B radiations. The results indicate that pigment-protein composition of Nostoc sp. stain HKAR-2 was significantly altered during diurnal variation of light/radiation, which might play an important role in optimization for their productivity in a particular cyanobacterium.

Interactive Effects of Temperature and UV Radiation on Photosynthesis of Chlorella Strains from Polar, Temperate and Tropical Environments: Differential Impacts on Damage and Repair

Global warming and ozone depletion, and the resulting increase of ultraviolet radiation (UVR), have far-reaching impacts on biota, especially affecting the algae that form the basis of the food webs in aquatic ecosystems. The aim of the present study was to investigate the interactive effects of temperature and UVR by comparing the photosynthetic responses of similar taxa of Chlorella from Antarctic (Chlorella UMACC 237), temperate (Chlorella vulgaris UMACC 248) and tropical (Chlorella vulgaris UMACC 001) environments. The cultures were exposed to three different treatments: photosynthetically active radiation (PAR; 400–700 nm), PAR plus ultraviolet-A (320–400 nm) radiation (PAR + UV-A) and PAR plus UV-A and ultraviolet-B (280–320 nm) radiation (PAR + UV-A + UV-B) for one hour in incubators set at different temperatures. The Antarctic Chlorella was exposed to 4, 14 and 20°C. The temperate Chlorella was exposed to 11, 18 and 25°C while the tropical Chlorella was exposed to 24, 28 and 30°C. A pulse-amplitude modulated (PAM) fluorometer was used to assess the photosynthetic response of microalgae. Parameters such as the photoadaptive index (E_k) and light harvesting efficiency (α) were determined from rapid light curves. The damage (k) and repair (r) rates were calculated from the decrease in ΦPSII_eff over time during exposure response curves where cells were exposed to the various combinations of PAR and UVR, and fitting the data to the Kok model. The results showed that UV-A caused much lower inhibition than UV-B in photosynthesis in all Chlorella isolates. The three isolates of Chlorella from different regions showed different trends in their photosynthesis responses under the combined effects of UVR (PAR + UV-A + UV-B) and temperature. In accordance with the noted strain-specific characteristics, we can conclude that the repair (r) mechanisms at higher temperatures were not sufficient to overcome damage caused by UVR in the Antarctic Chlorella strain, suggesting negative effects of global climate change on microalgae inhabiting (circum-) polar regions. For temperate and tropical strains of Chlorella, damage from UVR was independent of temperature but the repair constant increased with increasing temperature, implying an improved ability of these strains to recover from UVR stress under global warming.

Comparing Acute Effects of a Nano-TiO2 Pigment on Cosmopolitan Freshwater Phototrophic Microbes Using High-Throughput Screening

Production of titanium-dioxide nanomaterials (nano-TiO₂) is increasing, leading to potential risks associated with unintended release of these materials into aquatic ecosystems. We investigated the acute effects of nano-TiO₂ on metabolic activity and viability of algae and cyanobacteria using high-throughput screening. The responses of three diatoms (Surirella angusta, Cocconeis placentula, Achnanthidium lanceolatum), one green alga (Scenedesmus quadricauda), and three cyanobacteria (Microcystis aeruginosa, Gloeocapsa sp., Synechococcus cedrorum) to short-term exposure (15 to 60 min) to a common nano-TiO₂ pigment (PW6; average crystallite size 81.5 nm) with simulated solar illumination were assessed. Five concentrations of nano-TiO₂ (0.5, 2.5, 5, 10, and 25 mg L^-1) were tested and a fluorescent reporter (fluorescein diacetate) was used to assess metabolic activity. Algae were sensitive to nano-TiO₂, with all showing decreased metabolic activity after 30-min exposure to the lowest tested concentration. Microscopic observation of algae revealed increased abundance of dead cells with nano-TiO₂ exposure. Cyanobacteria were less sensitive to nano-TiO₂ than algae, with Gloeocapsa showing no significant decrease in activity with nano-TiO₂ exposure and Synechococcus showing an increase in activity. These results suggest that nanomaterial contamination has the potential to alter the distribution of phototrophic microbial taxa within freshwater ecosystems. The higher resistance of cyanobacteria could have significant implications as cyanobacteria represent a less nutritious food source for higher trophic levels and some cyanobacteria can produce toxins and contribute to harmful algal blooms.

Vulnerability and acclimation to increased UVB radiation in three intertidal macroalgae of different morpho-functional groups

The vulnerability and acclimation to increased UVB radiation in three macroalgae of different morpho-functional groups collected in the Mediterranean coastal waters were evaluated. The algae were submitted for 7 days to increased (PAB+) and decreased (PAB-) UVB radiation. The thickness and morphology influenced the response to increased UVB radiation, being Cystoseira tamariscifolia the less vulnerable algae followed by Ellisolandia elongata. The highest resistance to increased UVB radiation in C. tamariscifolia was related to the accumulation of polyphenols and high antioxidant activity, whereas E. elongata was due to its high reflectance. Finally, Ulva rigida suffered the highest photoinhibition under PAB+ culture. The latest species presented 10 times lower polyphenol content and antioxidant activity than C. tamariscifolia. The three species showed different acclimation patterns to the changes of UVB radiation related to the morphology, photosynthetic activity, accumulation of photoprotectors and antioxidant activities. The ecological implications of the UVB variations on macroalgae are discussed.

Sensitivity of photosynthesis to UV radiation in several Cosmarium strains (Zygnematophyceae, Streptophyta) is related to their geographical distribution

The application of UV radiation in vitro on desmid strains collected from various climatic areas and long-term grown under identical laboratory conditions revealed their preference for specific climatic niches, as judged from their different photosynthetic behaviours.

Protection strategies of Cosmarium strains (Zygnematophyceae, Streptophyta) isolated from various geographic regions against excessive photosynthetically active radiation

Numerous in vitro investigations have suggested that macroalgae exhibit regular geographic and depth distribution patterns in accordance with the light and temperature predominance at their habitats; however, there have been only a few similar studies concerning microalgae. We examined the potential influence of irradiance on patterns of distribution of four Cosmarium strains isolated from various climatic zones and cultured long term (>15 years) under a constant temperature-light regime. All the Cosmarium strains demonstrated physiological responses that were consistent with the light intensity prevailing at their source location, confirming that these responses are genetically preserved, as concluded from chlorophyll fluorescence and oxygen evolution rates measurements. Addition of inhibitors of chloroplast-encoded protein synthesis (chloramphenicol and streptomycin) and violaxanthin de-epoxidase (dithiothreitol) indicated that the Cosmarium strains developed "sun- or shade-plant" protection strategies, in accordance with the climate at their sampling sites. The polar Cosmarium strains exhibited a "shade-plant strategy"-to suffer some photoinhibition, but acquire increasing protection from photoinhibited PSII centers, whereas the tropical strains displayed a "sun-plant strategy"-to counteract photoinhibition of PSII by a high rate of repair of photoinhibited PSII reaction centers and a high xanthophyll cycle turnover.

NH4+ enrichment and UV radiation interact to affect the photosynthesis and nitrogen uptake of Gracilaria lemaneiformis (Rhodophyta)

Solar ultraviolet radiation (UVR, 280-400 nm) is known to inhibit the photosynthesis of macroalgae, whereas nitrogen availability may alter the sensitivity of the algae to UVR. Here, we show that UV-B (280-315 nm) significantly reduced the net photosynthetic rate of Gracilaria lemaneiformis. This inhibition was alleviated by enrichment with ammonia, which also caused a decrease in dark respiration. The presence of both UV-A (315-400 nm) and UV-B stimulated the accumulation of UV-absorbing compounds. However, this stimulation was not affected by enrichment with ammonia. The content of phycoerythrin (PE) was increased by the enrichment of ammonia only in the absence of UVR. Ammonia uptake and the activity of nitrate reductase were repressed by UVR. However, exposure to UVR had an insignificant effect on the rate of nitrate uptake. In conclusion, increased PE content associated with ammonia enrichment played a protective role against UVR in this alga, and UVR differentially affected the uptake of nitrate and ammonia.

Activation of violaxanthin cycle in darkness is a common response to different abiotic stresses: a case study in Pelvetia canaliculata

BACKGROUND

In the violaxanthin (V) cycle, V is de-epoxidized to zeaxanthin (Z) when strong light or light combined with other stressors lead to an overexcitation of photosystems. However, plants can also suffer stress in darkness and recent reports have shown that dehydration triggers V-de-epoxidation in the absence of light. In this study, we used the highly stress-tolerant brown alga Pelvetia canaliculata as a model organism, due to its lack of lutein and its non-photochemical quenching independent of the transthylakoidal-ΔpH, to study the triggering of the V-cycle in darkness induced by abiotic stressors.

RESULTS

We have shown that besides desiccation, other factors such as immersion, anoxia and high temperature also induced V-de-epoxidation in darkness. This process was reversible once the treatments had ceased (with the exception of heat, which caused lethal damage). Irrespective of the stressor applied, the resulting de-epoxidised xanthophylls correlated with a decrease in Fv/Fm, suggesting a common function in the down-regulation of photosynthetical efficiency. The implication of the redox-state of the plastoquinone-pool and of the differential activity of V-cycle enzymes on V-de-epoxidation in darkness was also examined. Current results suggest that both violaxanthin de-epoxidase (VDE) and zeaxanthin-epoxidase (ZE) have a basal constitutive activity even in darkness, being ZE inhibited under stress. This inhibition leads to Z accumulation.

CONCLUSION

This study demonstrates that V-cycle activity is triggered by several abiotic stressors even when they occur in an absolute absence of light, leading to a decrease in Fv/Fm. This finding provides new insights into an understanding of the regulation mechanism of the V-cycle and of its ecophysiological roles.

Tolerance to oxidative stress induced by desiccation in Porphyra columbina (Bangiales, Rhodophyta)

Unravelling the mechanisms underlying desiccation tolerance is crucial in order to understand the position of algal species in the intertidal zone. The alga Porphyra columbina lives in the uppermost part of the rocky intertidal zones around the world and was selected as a model for this study. Naturally desiccated plants were collected during low tide and studied for morphological changes, oxidative burst induction, biomolecule oxidation, antioxidant responses, and photosynthetic status. Naturally hydrated plants collected during high tides were used for comparative purposes. In addition, changes induced by desiccation were assessed in vitro and the capacity to recover from desiccation was determined by rehydrating the fronds in seawater. The global results show that desiccation induces morphological and cellular alterations accompanied by a loss of ∼96% of the water content. Overproduction of reactive oxygen species (ROS) was induced by desiccation and two peaks of H(2)O(2) were detected at 1 and 3 h of desiccation. However, during in vitro rehydration post-desiccation, the ROS quickly returned to the basal levels. At the biomolecular level, only a low production of oxidized proteins was recorded during desiccation, whereas the activity of diverse antioxidant enzymes increased. However, this activity diminished to near basal levels during rehydration. The photosynthetic efficiency (F(v)/F(m)) during desiccation declined by 94-96% of the values recorded in hydrated plants. This reduction was generated by the low levels of trapped energy flux per cross-section (TRo/CS), electron transport flux per CS (ETo/CS), and density of reaction centres (RC/SCo) as well as the chlorophyll content. The inverse pattern was observed for the levels of phycocyanin and phycoerythrin content. F(v)/F(m) and the photosynthetic indicators were restored to normal levels after only 5 min of rehydration. The results indicate that desiccation in P. columbina causes overproduction of ROS that is efficiently attenuated. The morphological and photosynthetic changes could be operating as tolerance mechanisms due to the fact that these responses principally prevent biomolecular alteration and cellular collapse. Thus, the activation of different physiological mechanisms helps to explain the high tolerance to desiccation of P. columbina and, at least in part, the position of this species at the highest level in the intertidal zone.

The supramolecular architecture, function, and regulation of thylakoid membranes in red algae: an overview

Red algae are a group of eukaryotic photosynthetic organisms. Phycobilisomes (PBSs), which are composed of various types of phycobiliproteins and linker polypeptides, are the main light-harvesting antennae in red algae, as in cyanobacteria. Two morphological types of PBSs, hemispherical- and hemidiscoidal-shaped, are found in different red algae species. PBSs harvest solar energy and efficiently transfer it to photosystem II (PS II) and finally to photosystem I (PS I). The PS I of red algae uses light-harvesting complex of PS I (LHC I) as a light-harvesting antennae, which is phylogenetically related to the LHC I found in higher plants. PBSs, PS II, and PS I are all distributed throughout the entire thylakoid membrane, a pattern that is different from the one found in higher plants. Photosynthesis processes, especially those of the light reactions, are carried out by the supramolecular complexes located in/on the thylakoid membranes. Here, the supramolecular architecture, function and regulation of thylakoid membranes in red algal are reviewed.

Impacts of UV radiation on growth and photosynthetic carbon acquisition in Gracilaria lemaneiformis (Rhodophyta) under phosphorus-limited and replete conditions

Solar ultraviolet radiation (UVR, 280-400 nm) is known to negatively affect macroalgal growth and photosynthesis, while phosphorus availability may affect their sensitivity to UVR. Here, we show that UV-A enhanced the growth rate of the red macroalga, Gracilaria lemaneiformis Bory de Saint-Vincent under inorganic phosphorus (Pi)-replete but reduced it under Pi-limited conditions. Maximal net photosynthetic rates were significantly reduced by both UV-A and UV-B, but the apparent photosynthetic efficiency was enhanced in the presence of UV-A. The UV-induced inhibition was exacerbated under Pi-limited conditions. The activity of total carbonic anhydrase was enhanced and the photosynthetic affinity for exogenous inorganic carbon (Ci) was raised for thalli grown in the presence of UVR under both Pi-replete and Pi-limited conditions. The relative growth rate was closely related to Ci acquisition capability (V_max/K_DIC), which was enhanced by UVR exposure under Pi-replete but not significantly affected under Pi-limited conditions.

BIOLOGICAL WEIGHTING FUNCTIONS FOR UV INHIBITION OF PHOTOSYNTHESIS IN THE KELP LAMINARIA HYPERBOREA (PHAEOPHYCEAE)(1)

Different wavelengths of sunlight either drive or inhibit macroalgal production. Ultraviolet radiation (UVR) effectively disrupts photosynthesis, but since UVR is rapidly absorbed in coastal waters, macroalgal photoinhibition and tolerance to UVR depend on the depth of attachment and acclimation state of the individual. The inhibition response to UVR is quantified with a biological weighting function (BWF), a spectrum of empirically derived weights that link irradiance at a specific wavelength to overall biological effect. We determined BWFs for shallow (0 m, mean low water [MLW]) and deep (10 m) Laminaria hyperborea (Gunnerus) Foslie collected off the island of Finnøy, Norway. For each replicate sporophyte, we concurrently measured both O2 evolution and (13) C uptake in 48 different light treatments, which varied in UV spectral composition and irradiance. The relative shape of the kelp BWF was most similar to that of a land plant, and the absolute spectral weightings and sensitivity were typically less than phytoplankton, particularly in the ultraviolet radiation A (UVA) region. Differences in BWFs between O2 and (13) C photosynthesis and between shallow (high light) and deep (low light) kelp were also most significant in the UVA. Because of its greater contribution to total incident irradiance, UVA was more important to daily loss of production in kelp than ultraviolet radiation B (UVB). Photosynthetic quotient (PQ) also decreased with increased UVR stress, and the magnitude of PQ decline was greater in deepwater kelp. Significantly, BWFs assist in the comparison of biological responses to experimental light sources versus in situ sunlight and are critical to quantifying kelp production in a changing irradiance environment.

Participation of the inositol phospholipid signaling pathway in the increase in cytosolic calcium induced by tributyltin chloride intoxication of chlorophyllous protozoa Euglena gracilis Z and its achlorophyllous mutant SM-ZK

Exposure of tri-n-butyl tin chloride (TBTCl) as a stressor to Euglena gracilis Z causes rapid alteration of cell morphology followed by deflagellation. The present study was undertaken to reveal the mechanism of the cell response at a molecular level. Chlamydomonas reinhardtii, in this study E. gracilis Z and its achlorophyllous mutant SM-ZK, gave similar results when subject to the same stressor. Indeed, similar results were obtained with both strains. Next, assuming that the morphological alteration caused by TBTCl is mediated by the inositide phosphate-lipid signaling pathway, the effects of signal transduction and Ca2+ release reagents (mastoparan as a G-protein activator, neomycin as a phospholipase C inhibitor, verapamil as a Ca2+ channel blocker, and A23187 as a Ca2+ ionophore) on morphology and intracellular Ca2+ levels were examined with or without TBTCl. The data strongly suggest that the morphological alteration is mediated by an increase in Ca2+ linked to the inositol phosphatide pathway. The cellular response to signal transduction inducing reagents was compared between the E. gracilis chlorophyllous Z strain and its achlorophyllous mutant SM-ZK strain. Significant differences were observed between the Z and SM-ZK strains in terms of the stress response and intracellular Ca2+ level.

Parallel changes in non-photochemical quenching properties, photosynthesis and D1 levels at sudden, prolonged irradiance exposures in Ulva fasciata Delile

The photosynthetic response to a sudden and prolonged high irradiance exposure and following recovery at low irradiance were studied with the aim of investigating the ability to withstand and adapt to high irradiance without prior high light adaptation. When thalli of Ulva fasciata, accustomed to a low irradiance (80 micromol photons m(-2) s(-1)), were exposed to a high irradiance (1500 micromol photons m(-2) s(-1)), the D1 protein was rapidly degraded, reaching a steady-state level after 110 min. This was followed by a fast recovery when thalli were transferred to dim light. The overall ability of non-photochemical quenching of chlorophyll fluorescence decreased and levelled off at a sudden and prolonged exposure to high irradiance and followed the same trend as the D1 level with a fast recovery in dim light. Ulva had intrinsic means to acclimate rapidly to high irradiance, when non-photochemical quenching did not operate properly, by maintaining a smaller fraction of high light tolerant PSII assemblages and by maintaining a high non-photochemical quenching capacity of chlorophyll fluorescence in relation to the variable fluorescence. The overall absorption of light (400-700 nm) remained high during the period of high irradiance exposure. When Ulva were deprived of nutrients in the form of PES media the ability of non-photochemical quenching decreased at photoinhibitory conditions. The possible causes for the responses at prolonged irradiance and the mechanisms for the decrease of non-photochemical quenching are discussed, with implications for field measurements.

A Five-year Study of Solar Ultraviolet Radiation in Southern Chile (39° S): Potential Impact on Physiology of Coastal Marine Algae?

This study reports 5 years of (1998-2003) data on continuous solar-irradiation measurements from a scanning spectroradiometer (SUV-100) in Valdivia, Chile (39 degrees S), accompanied by evaluation of the impact of ultraviolet radiation (UVR) on marine macroalgae of this site. UVR conditions showed a strong seasonal variation, which was less pronounced toward longer wavelengths. Daily maximum dose rates (clear days) averaged in winter-summer: UV-B(290-315 nm) 0.30-2.1, UV-B(290-320 nm) 0.70-3.7, UV-A(315-400 nm) 20.6-62.1, UV-A(320-400 nm) 20.2-60.5 W m(-2), and photosynthetically active radiation (PAR) 969-2423 micromol m(-2) s(-1). The corresponding daily doses (all the days) ranged: UV-B(290-315 nm) 2.6-40.7, UV-B(290-320 nm) 6.7-78.5, UV-A(315-400 nm) 228-1539, UV-A(320-400 nm) 224-1501, and PAR 2008-13308 kJ m(-2) d(-1). Taking into consideration action spectra of a biological interest, the risk of UV exposure could be up to 37 times higher in summer than in winter. The photosynthetic activity (as maximum quantum yield of chlorophyll fluorescence, F(v)/F(m)) of the brown alga Lessonia nigrescens from the infralittoral zone was markedly more sensitive to UVR than of the green alga Enteromorpha intestinalis from the upper midlittoral, and the UV-B wave band increased markedly photoinhibition. In L. nigrescens, maximal photoinhibition (40%) took place at weighted (the action spectrum for photoinhibition of photosynthesis) UVR doses of 800 kJ m(-2), irrespective of the season (corresponding midsummer daily dose in Valdivia is 480 kJ m(-2)). In winter, when this alga was at its most sensitive, the weighted UV dose causing 35-40% photoinhibition was around 200 kJ m(-2). In E. intestinalis, weighted doses of 800 kJ m(-2) resulted in low photoinhibition (<10 %) and no clear seasonal patterns could be inferred. These results confirm that midday summer levels of UV-B and their daily doses in southern Chile are high enough to produce stress to intertidal macroalgae.

Dynamics of potentially protective compounds in Rhodophyta species from Patagonia (Argentina) exposed to solar radiation

The impact of solar radiation upon potentially protective compounds (i.e., UV-absorbing compounds and carotenoids) was assessed in four Rhodophyte species from Patagonia (i.e., Ceramium sp. Lyngbye, Corallina officinalis Linnaeus, Callithamnion gaudichaudii Agardh and Porphyra columbina Montagne) during short-term (i.e., 46 h) experiments. Algae were exposed to solar radiation under two treatments (PAR only: 400-700 nm, and PAR+UVR: 280-700 nm) and sub-samples were taken every 3 h (or longer periods at night) to determine the spectral absorption characteristics and concentration of UV-absorbing compounds, carotenoids and photosynthetic pigments. Except for C. gaudichaudii which displayed a decrease in chl-a concentration throughout the experiment, photosynthetic pigments had small variations in all species. UV-absorbing compounds concentration had species-specific responses: Ceramium sp. was the only species in which UV-absorbing compounds concentration varied as a function of solar irradiance, with maximum values around local noon. In C. officinalis and P. columbina UV-absorbing compounds concentration increased as compared to that of chl-a; in Ceramium sp. and C. gaudichaudii, however, there was no relationship between UV-absorbing compounds content and chl-a concentration. Carotenoids, on the other hand, did co-vary with chl-a in all species. Our data suggest that, with the exception of C. gaudichaudii, the differential responses of UV-absorbing compounds concentrations are more associated to the previous light history of the algae (i.e., in turn due to their position in the intertidal zone) rather than to the radiation treatment imposed to the samples. Based on our results, the variable impact of solar radiation upon productivity (and eventually biodiversity) of macroalgae from Patagonia might consequently differentially affect higher trophic levels of the aquatic food web.