Silver nanoparticles toxicity effect on photosystem II photochemistry of the green alga Chlamydomonas reinhardtii treated in light and dark conditions

The inhibitory effect of silver nanoparticles (AgNPs) on photochemical reactions of photosynthesis was investigated using the green alga model Chlamydomonas reinhardtii. Algal cells were exposed to 1, 5, and 10?µmol?L^?1 of AgNPs under both light and dark conditions during 6?h. The rapid rise of chlorophyll a fluorescence and the fluorescence imaging system were employed to investigate the alteration of photosystem II (PSII) photochemical reactions and the associated electron transport activity. When algal cells were exposed to 5 and 10?µmol?L^?1 of AgNPs, our results showed the evidence of a structural deterioration of PSII reaction center, the alteration of the oxygen evolving complex and the inhibition of electron transport activity, which was stronger for AgNPs treatment under light exposure. Under these conditions, there was no activation of regulated photoprotective mechanisms against excess absorbed light-energy by the antenna system of the PSII complex. The highest deteriorating effect on the structural and functional integrity of PSII was observed for algal cells exposed 6?h in light condition to 10?µmol?L^?1 of AgNPs. Therefore, we provide valuable data in this study permitting to use photosynthetic-based fluorescence parameters for aquatic toxicological risk investigation of polluted water that may contain AgNP suspension.     

Cell cycle of symbiotic dinoflagellates: variation in G1 phase-duration with anemone nutritional status and macronutrient supply in the Aiptasia pulchella–Symbiodinium pulchrorum symbiosis

The metabolite exchange in alga–invertebrate symbioses has been the subject of extensive research. A central question is how the biomass of the algal endosymbionts is maintained within defined limits under a given set of environmental conditions despite their tremendous growth potential. Whether algal growth is actively regulated by the animal cells is still an open question. We experimentally evaluated the effect of inorganic nutrient supply and host-animal nutritional status on the biomass composition, growth and cell-cycle kinetics of the endosymbiotic dinoflagellate Symbiodinium pulchrorum (Trench) in the sea anemone Aiptasia pulchella. Dinoflagellates in anemones starved for 14?d exhibited lower growth rates, chlorophyll content and higher C:N ratios than in anemones fed Artemia sp. (San Francisco brand #65034) nauplii every 2 d, indicating N-limitation of the algae during starvation of the host animal. Manipulation of the dissolved inorganic nutrient supply through ammonium and phosphate additions induced a rapid recovery (half time, t _½～ 2?d) in the C:N ratio of the dinoflagellate cells to levels characteristic of N-sufficient cells. The mitotic index and population growth rate of the dinoflagellate symbionts subjected to this enrichment did not recover to the levels exhibited in fed associations. Flow cytometric analysis of dinoflagellate cell size and DNA content revealed that the duration of the G₁ phase (first peak of DNA content: 70 to 100 relative fluorescence units, rfu) of their cell cycle lengthened dramatically in the symbiotic state, and that the majority of algal biomass increase occurred during this phase. Covariate analysis of dinoflagellate cell size and DNA-content distributions indicated that the symbiotic state is associated with a nutrient-independent constraint on cell progression from G₁ through the S phase (intermediate DNA content: 101 to 139?rfu). This analysis suggests that the host-cell environment may set the upper limit on the rate of dinoflagellate cell-cycle progression and thereby coordinate the relative growth rates of the autotrophic and heterotrophic partners in this symbiotic association.     

Diurnal and circadian rhythms in the turbidity of growing Skeletonema costatum cultures

Skeletonema costatum (Grev.) Cleve grown in batch culture at low light intensity under a 14 h light: 10 h dark photocycle showed exponential cell proliferation (1.1 doublings d^-1) without significant phasing of the cell division by the light: dark cycle. The growth in carbon concentration was, however, restricted to the light period. The turbidity of the culture closely followed the carbon oattern, and was not affected by the increase in the cell number during the dark period. It was found that a trustule suspension had only approximately 1% of the turbidity of the corresponding intact algae. Culture turbidity was therefore regarded as a biomass parameter similar to the carbon concentration, without direct correlation to the timing of the cell division. The short-time variations in the turbidity of growing algal cultures were further studied in a cage culture turbidostat. The growth rate (based on turbidity) increased rapidly during the first half of the light period, decreased slightly towards the evening and was zero throughout the dark period. When transformed to continuous light, the growth of the culture continued to show damped oscillations for up to 1 wk, but with a period of 26.7 h instead of 24 h. The same circadian rhythm was observed in chlorophyll content, and is thus possibly a reflection of a freely oscillating internal biological clock. The cage culture turbidostat was found to be a suitable device for studies of the photocycle related regulation of biosynthesis in S. costatum.     

DNA synthesis and the cell cycle in the noxious red-tide dinoflagellateGymnodinium nagasakiense

Gymnodinium nagasakiense is a noxious red tide dinoflagellate often associated with damage to fisheries in Japan. DNA synthesis and the cell cycle in this organism were investigated from 1989 to 1990 by determining relative DNA contents of individual cells using an epifluorescence microscopy-based microfluorometry system. The nuclei were stained with the DNA-specific fluorochrome 4-6-diamidino-2-phenylindole (DAPI). Because photosynthetic pigment interferes with the fluorescence from the DAPI-DNA complex, the pigment was eliminated by methanol treatment as a first step in quantitative microfluorometry. Nuclear DNA contents, cell size distribution, cell density, and frequency of paired cells were determined every 2h for 24h using cells grown on a 12h light:dark cycle. DNA synthesis and cell division were tightly phased to a particular period of the light:dark cycle. DNA synthesis (S phase) occurred from 10:00 to 22:00 hrs and was followed by cytokinesis. The presence of such a distinct S phase strongly suggests thatG. nagasakiense has a typical eukaryotic cell cycle. This type of cell cycle makes it possible to estimate speciesspecific in situ growth rate based on the diel pattern of DNA synthesis.     

Mechanisms of photoadaptation in three strains of the symbiotic dinoflagellate Symbiodinium microadriaticum

Mechanisms of photoadaptation of photosynthesis have been studied in three strains of the symbiotic dinoflagellate Symbiodinium microadriaticum. Algal strains isolated from the clam Tridacna maxima, the sea anemone Aiptasia pulchella, and the scleractinian coral Montipora verrucosa were maintained in the defined medium ASP-8A, and were grown at irradiances ranging from 22 to 248 μE m^-2 s^-1 on a 14 h:10 h (light:dark) photoperiod at 26°C. All algal cultures were analysed during log-phase of growth. At all light levels, rates of cell division and photosynthesis were determined, as were cell volumes, pigmentation (including chlorophyll a, chlorophyll c ₂, peridinin, β-carotene and xanthophylls), and carbon and nitrogen content. Low light-induced changes in pigmentation were evident to varying degrees in all three algal strains, although alterations in the photosynthesis-irradiance relations were distinctly different in each strain. The algae from T. maxima show the least photoadaptive capability, and seem to photoadapt by changing photosynthetic unit (PSU) size. Algae from A. pulchella appear to adapt by changing PSU number, while algae from M. verrucosa appear to photoadapt by changes in the activities of CO₂-fixing enzymes or electron transport systems. These are the first observations that demonstrate functional differences in different strains of S. microadriaticum. The adaptive capabilities of the algae appear to correlate well with the ecological distribution of their respective hosts. The study was made from July 1981 through December 1982.     

Kinetics of light-intensity adaptation in a marine planktonic diatom

The marine planktonic diatom Thalassiosira weisflogii was grown in turbidostat culture under both continuous and 12 hL: 12 hD illumination regimes in order to study the kinetics of adaptation to growth-irradiance levels. In both illumination regimes adaptation to a higher growth-irradiance level was accompanied by an increase in cell division rates and a decrease in chlorophyll a cell^-1. The rates of adaptation for both processes, derived from first order kinetic analysis, equaled each other in each experiment. The results suggest that during the transition from low-to-high growth-irradiance levels chlorophyll a is diluted by cell division and is not actively degraded. Introduction of a light/dark cycle lowered the rate of adaptation. In transitions from high-to-low growth-irradiance levels there was a sharp drop in growth rates and a slow increase in chlorophyll a cell^-1 under both continuous and intermittent illumination. In the 12 hL:12hD cycle there was a circadian rhythm in chlorophyll a cell^-1, where cellular chlorophyll contents increased during the light cycle and decreased during the dark cycle. This circadian rhythm was distinctly different from light intensity adaptation. For kinetic analysis of light intensity adaptation in a 12 hL: 12 hD cycle, the circadian periodicity was separated from the light intensity response by subjecting the data to a Kaiser window optimization digital filter. Kinetic parameters for light-intensity adaptation were resolved from the filtered data. The kinetics of lightintensity adaptation of marine phytoplankton are discussed in relation to their spatial variations and time scales of mixing.This research was performed at Brookhaven National Laboratory under the auspices of the United States Department of Energy under Contract No. DE-AC02-76 CH00016     

Protective effect of Kappaphycus alvarezii (Rhodophyta) extract against DNA damage induced by mercury chloride in marine fish

Marine organisms are continuously exposed to agents, both exogenous and endogenous, that damage DNA. Consequently, it is important to determine the ability of compounds to provide protection against damaging chemicals. The aim of this study was to evaluate the anti-genotoxic activity of crude aqueous extracts of Kappaphycus alvarezii (Rhodophyceae), collected from the Southeast coast of India. This study focused on possible anti-genotoxic potential of aqueous extract of K. alverazii to interfere with clastogenicity induced by mercury chloride (HgCl₂) in marine fish, Therapon jarbua as measured by cytogenetic endpoints such as cell viability and comet assay. In the first set of experiments, fish were exposed to a single treatment of Hg at 0.125, 0.25, 0.5, 1, or 2?ppm along with controls. Mercury exposure produced significant DNA damage in all comet classes, maximum as >79% (Class 4) at 0.5, 1, and 2?ppm exposure in a time dependent manner. Algal extract did not induce genotoxicity when given alone and prevented Hg-induced genotoxicity. The algal extract reduction in genotoxicity was significant but not time- and concentration-dependent. Results suggested that under present experimental conditions, K. alvarezii extract exhibit potent anti-genotoxicity effects in this fish model; and thus these extracts may be recommended as a supplement in fish meal and may benefit humans ingesting Hg-contaminated fish.     

Carbon and nitrogen metabolism by Monochrysis lutheri: Measurement of growth-rate-dependent respiration rates

Dark respiration rates were measured and carbon-excretion rates calculated for a nitrate-limited population of the marine chrysophyte Monochrysis lutheri grown in continuous culture at 20°C on a 12 h light-12 h dark cycle of illumination and over a series of 4 growth rates. A significant (P<0.05) positive correlation was found between dark respiration rate and growth rate. From a simple linear fit to the data, the respiration rate at maximum growth rate was estimated to be roughly 10.5% of the maximum gross-carbon-production rate, and more than three times higher than the extrapolated respiration rate at zero net-growth rate. Carbon-excretion rates showed no significant correlation with growth rate, and averaged less than 5% of the maximum gross-carbon-production rate. Mean cell nitrogen to carbon ratios were correlated in a virtually linear manner (r=0.994) with growth rate, and at a given growth rate were consistently higher than nitrogen to carbon ratios for the same species grown on continuous light. A comparison of carbon and nitrogen quotas as a function of growth rate for M. lutheri and other species suggests that the increase of cellular nitrogen at high growth rates under nitrate-limited growth conditions may be associated with the storage of cellular protein or amino acids rather than the presence of an inorganic nitrogen reservoir. The maximum nitrate uptake rate per cell during the day changed very little over the range of growth rates studied, and was comparable to the maximum uptake rate found for cells grown on continuous light. However, the cell nitrogen quota increased steadily with growth rate, causing a reduction in the maximum specific-uptake rate of nitrate during the day at high growth rates. The dark nitrate-uptake capacity of the population was clearly exceeded by the supply rate at the two higher growth rates, leading to a buildup of nitrate during the night which amounted to as much as 21% of the particulate nitrogen in the growth chamber by morning.Hawaii Institute of Marine Biology Contribution No. 478.     

Removing nitrogen and phosphorus from simulated wastewater using algal biofilm technique

Algal biofilmtechnology is a new and advanced wastewater treatment method. Experimental study on removing nitrogen and phosphorus from simulated wastewater using algal biofilm under the continuous light of 3500 Lux in the batch and continuous systems was carried out in this paper to assess the performance of algal biofilm in removing nutrients. The results showed that the effect of removing nitrogen and phosphorus by algal biofilm was remarkable in the batch system. The removal efficiencies of total phosphorus (TP), total nitrogen (TN), ammonia-nitrogen (NH₃-N), and chemical oxygen demand (COD) reached 98.17%, 86.58%, 91.88%, and 97.11%, respectively. In the continuous system, hydraulic retention time (HRT) of 4 days was adopted; the effects of removing TP, TN, NH₃-N, and COD by algal biofilm were very stable. During a run of 24 days, the removal efficiencies of TP, TN, NH₃-N, and COD reached 95.38%, 83.93%, 82.38%, and 92.31%, respectively. This study demonstrates the feasibility of removing nitrogen and phosphorus from simulated wastewater using algal biofilm.     

Changes in the acitivy of fucoxanthin-excited photosynthesis in the marine diatom Phaeodactylum tricornutum grown under different culture conditions

Variations in the photosynthetic activity under monochromatic light was studied in Phaeodactulum tricornutum grown under various culture conditions, with special reference to the composition of photosynthetic pigments. Photosynthetic activity, under light-limiting conditions, was reduced when the cells were grown under strong light. The reduction was more extensive in activity resulting from fucoxanthin-excitation than in that from chlorophyll a-excitation. The diminution in activity for fucoxanthin-excited photosynthesis did not correlate with variations in the pigment content. A similar diminution was observed with chlorophyll a fluorescence upon excitation of fucoxanthin. The change was accelerated by lowering the culture temperature, or limiting the supply of nitrogen source. The results were interpreted in terms of a nitrogen-deficient state for algal cells induced by strong light, low temperature or a limited supply of nitrogen. This leads to a modification of the physicochemical state of in vivo fucoxanthin, so that the excitation energy of fucoxanthin is less efficiently transferred to chlorophyll a. The significance of the phenomenon in the oceanic primary production is discussed.     

Cell cycle and toxin production in the benthic dinoflagellate Prorocentrum lima

Profiles of diarrhetic shellfish poisoning (DSP) toxins produced throughout the growth cycle and the cell cycle of the toxigenic marine dinoflagellate Prorocentrum lima were studied in triplicate unialgal batch cultures. Cells were pre-conditioned at 18 ± 1 °C, under a photon flux density (PFD) of 90 ± 5 μmol m⁻² s⁻¹ on a 14 h light:10 h dark photoperiod. In exponential growth phase, cultures were synchronized in darkness for 17 d. After dark synchronization, cultures were transferred back to the original photoperiod regime. Cells were harvested for DSP toxin analysis by LC-MS (liquid chromatography with mass spectrometry), and double-stranded (nuclear) DNA was quantified by flow cytometry. The cell populations became asynchronous within approximately 3 d after transition from darkness to the 14 h light:10 h dark photoperiod. This may be due to the prolonged division cycle (5 to 7 d) that is not tightly phased by the photoperiod. Unlike other planktonic Prorocentrum spp., cytokinesis in P. lima occurred early in the dark and ceased by “midnight”. Cellular levels of the four principal DSP toxins, okadaic acid (OA), OA C8-diol-ester (OA-D8), dinophysistoxin-1 (DTX1) and dinophysistoxin-4 (DTX4), ranged from 0.37 to 6.6, 0.02 to 1.5, 0.04 to 2.6, and 1.8 to 7.8 fmol cell⁻¹, respectively. No toxin production was evident during the extended period of dark synchronization nor during the initial period when NH₄ was consumed as the major nitrogen source. Soon after the cells were returned to the 14 h light:10 h dark cycle and they began to take up NO₃, cellular levels of all four toxins gradually increased. This increase in DSP toxins usually occurred in the light, marked by a rise in DTX4 levels that preceded an increase in the cellular concentration of OA and DTX1 (delayed by 3 to 6 h). Thus, DTX4 synthesis is initiated in the G1 phase of the cell cycle and persists into S phase (“morning” of the photoperiod), whereas OA and DTX1 production occurs later during S and G2 phases (“afternoon”). No toxin production was measured during cytokinesis, which happened early in the dark. The evidence indicates that toxin synthesis is restricted to the light period and is coupled to cell cycle events. Received: 3 September 1998 / Accepted: 30 March 1999     

Growth and competition of the marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. II. Light limitation

The marine diatoms Phaeodactylum tricornutum (Bohlin) and Thalassiosira pseudonana (Hasle and Heimdal) were grown under both continous illumination and a 14 h light: 10 h dark cycle at light intensities ranging from 1.53×10^-4 to 2.95×10^-1 ly min^-1. Under both photoperiods, T. pseudonana exhibited higher division rates than P. tricornutum at high light intensities, but the reverse was true at all light intensities <3×10^-3 ly min^-1. Comparison of these results with available data on light-limited growth of other planktonic algae suggests that P. tricornutum may be unusually efficient at maintaining its cell division rate at low light intensity. This efficiency may contribute substantially to its success in turbid, nutrient-enriched mass algal culture systems, the only environments in which it is known to attain great numbers.Contribution No. 4086 from the Woods Hole Oceanographic Institution.     

Morphology, molecular phylogeny and photosynthetic activity of the sacoglossan mollusc, Elysia nigrocapitata, from Korea

The morphology, external coloration as well as the life span of a kleptoplastic mollusc, Elysia nigrocapitata, was affected by its algal diet. Among algal diets, Chaetomorpha moniligera was the best for growth but not for animal longevity. TEM studies showed several distinctive layers composed of different cell types in sectioned parapodia. The chloroplast-containing digestive cells were located beneath the layer of vacuolated cells. The digestive cells contained 10–15 chloroplasts, in varying states of intactness, and several nuclei. Chloroplasts were not enclosed by any membranous structure in the host cytosol. Chlorophyll a fluorometry showed that the photosynthetic activity of kleptoplasts in E. nigrocapitata could be maintained for a long time only when animals were kept in the dark. The photosynthetic activity of kleptoplasts lasted 3–4 days when the animals were exposed to continuous illumination of 200 μmol photons m^?2 s^?1. These results suggested that the contribution of kleptoplasts to the survival of the animals might be minimal if the chloroplasts are not sequestered continuously. Cox I, 16S rDNA, and 28S rDNA sequence data have been obtained in order to phylogenetically place the new species of Elysia found in Korea.     

Carbohydrate metabolism in the marine diatom Skeletonema costatum

This is a study on the metabolism of the algal biochemical constituents of a marine diatom, Skeletonema costatum. The carbohydrates, protein, and lipid, of the diatom grown under light and dark conditions were analyzed. The composition of the organic compounds did not vary in the alga grown under continuous light conditions throughout the experiment, although a little accumulation of carbohydrate and lipid was observed in the stationary phase of the algal growth. When the diatom, at maximum growth stage, was transferred to darkness, 44.4% of the carbohydrate, 57.8% of the protein, and 27.0% of the lipid were used by respiration within a few days. Detailed analysis of the algal carbohydrate demonstrated that low molecular weight carbohydrates, consisting of glucose, and -1,3-glucan, were readily metabolized by algal respiration, leaving cell-wall carbohydrates consisting of mannan and pentosan which are immune to algal respiration. The respiratory utilization of carbohydrates is discussed in relation to the rapid decay of glucan from marine particulate matter during the course of its sinking to further depths in the ocean, as observed previously by the present author.     

Intraspecific variation of photosynthesis,respiration and photoprotective carotenoids in<Emphasis Type="Italic"> Gracilaria birdiae</Emphasis> (Gracilariales: Rhodophyta)

In most rhodophytes, the quenchers zeaxanthin or lutein seem to be used for carotenoid photoprotection next to β-carotene. However, our study shows that the tropical intertidal alga Gracilaria birdiae possesses high concentrations of antheraxanthin, as well as lower concentrations of both zeaxanthin and violaxanthin. In higher plants and some algal groups, these three oxygenated carotenoids are known to protect photosystem II in a xanthophyll cycle. We were able to manipulate the carotenoid concentrations in G. birdiae by varying irradiance and temperature in laboratory experiments. Higher concentrations of violaxanthin were found in dark incubations and higher concentrations of zeaxanthin in light incubations, which is an indication that a xanthophyll cycle is active in G. birdiae. Our results also suggest a biosynthesis pathway from lycopene to β,β-carotene and β-cryptoxanthin in the light and synthesis of new lycopene in darkness. This would imply that the production of functional carotenoids is regulated by their need in photoprotection. Despite cultivation in the laboratory under the same conditions for at least 6 years, there were differences in photosynthetic properties and carotenoid dynamics between algae obtained from a population close to the Equator and another population close to the Tropic of Capricorn. These differences most probably have their origin in genetic differentiation mediated by ambient irradiance and temperature regimes. Four phycoerythrin-deficient mutant strains of G. birdiae were studied as well. Photosynthetic properties and carotenoid dynamics were basically the same in the mutants and the wild strains, but two green strains had remarkably low dark respiratory rates. This is an indication of low production of metabolites, which may be a competitive disadvantage.     

锌在不同磷源条件下对铜绿微囊藻生长与产毒的影响

针对磷和微量元素对藻类生长的共同作用,研究不同磷源条件下锌对藻细胞生长与产毒的影响。实验选用铜绿微囊藻为藻种,分别以无机磷磷酸氢二钾(K_2HPO_4)、小分子有机磷甘油磷酸钠(NaGly)和大分子有机磷卵磷脂(LEC)为磷源,研究不同锌(Zn~(2+))含量对藻细胞的藻密度、碱性磷酸酶活性(alkaline phosphatase activity,APA)以及胞内藻毒素(MC-LR)的影响。研究发现:以NaGly为磷源时微量元素锌对藻细胞生长的促进效果显著,而以K_2HPO_4或LEC为磷源时,锌含量的变化对藻细胞生长无显著影响。APA不仅与磷源有关而且与锌含量相关,以LEC为磷源时的APA显著高于以K_2HPO_4或NaGly为磷源时的APA,且锌含量越低APA越低,以K_2HPO_4为磷源时锌含量越低APA越高,而锌对以NaGly为磷源时的APA几乎没有影响。磷源与微量元素锌对藻细胞的产毒均产生影响,NaGly有利于藻毒素的产生; LEC不利于藻细胞的产毒,但锌含量越低藻细胞的产毒量越多。综上所述,磷源与微量元素锌共同作用对藻细胞的生长与产毒产生影响,小分子有机磷NaGly与锌的效果显著。     

Grazing effects on nitrogen fixation in coral reef algal turfs

This study addressed whether grazing by the sea urchin Diadema antillarum influenced rates of nitrogen fixation by algal turf communities on Caribbean coral reefs. Because the turfs were nitrogen-limited, we also assessed whether newly-fixed nitrogen was important for supporting net primary productivity by the turfs. We measured acetylene reduction in turfs grown in treatments excluding or including D. antillarum in the presence of other herbivores at 3 m water depth on Tague Bay forereef, St. Croix, U.S. Virgin Islands. These were the first measurements of acetylene reduction on coral reefs under quasi-natural conditions of high water-flow and photosynthetic oxygen generation. Rates of acetylene reduction under these conditions were as high as any measured previously in coral reef communities (mean 7.6 nmol C₂H₄ cm⁻² h⁻¹). Algal turfs grazed by D. antillarum and other herbivores had chlorophyll-specific acetylene reduction rates up to three times higher than when D. antillarum was excluded. High rates of nitrogen fixation by the turfs were sufficient to meet <2% of the nitrogen required to support net chlorophyll-specific primary productivity over 24 h. Grazer-mediated increases in nitrogen fixation do not appear responsible for a parallel enhancement of net primary productivity. Algal turfs at this site must be dependent primarily on external sources of nitrogen. Received: 1 July 1997 / Accepted: 5 September 1997     

Photosynthetic performance,oxidative damage and antioxidants in <Emphasis Type="Italic">Cylindrotheca closterium</Emphasis> in response to high irradiance,UVB radiation and salinity

Cylindrotheca closterium is a common marine diatom living in intertidal environments where it can be present both in the water column and on sediments, depending on the tidal regime. In the present work this diatom was employed to investigate the responses to desiccation and to increase in PAR and UVB intensity, as occurs during emersion. Under these circumstances, the production of active oxygen species (AOS) may be enhanced resulting in an oxidative stress. Stress responses in this species were measured by exposing it to normal (30) and double salinity (60), supplying light of low or high intensity for 12 h, in the latter case either without or with moderate dose rates of UVB. Pulse amplitude modulated fluorometry was used to measure Chl a autofluorescence (F ₀), an index of photosynthetic efficiency of PSII (F _v/F _m) and the relative electron transfer rate (rETR). The oxidative stress was evaluated by analysing GSH pools and SOD activity. It was observed that at double salinity and under low light, intracellular pools of reduced glutathione (GSH) were higher than under the two conditions of high light without and with UVB at both salinities. The antioxidative defence activity of superoxide dismutase (SOD) was far higher under hypersaline conditions. The oxidative damage was evaluated as protein and lipid damage. The results showed that it expressed itself mainly through protein peroxidation: at normal salinity relative protein carbonyl content was (a) twice as high as in cells grown at double salinity, and (b) three times as high under UVB. Total unsaturated lipid contents doubled under hypersalinity conditions. The lipid peroxidation marker malondialdehyde showed the strongest response to low light and UVB at salinity value of 60. Lipid peroxide content was significantly higher at salinity of 60 compared to normal salinity and was the highest under low light and high light with UVB. The simulated emersion condition of the diatom seems to lead to the establishment of a balance between damage and repair, expressed mainly as (a) oxidative protein damage at normal salinity, in particular due to UV radiation, (b) sufficient protection by SOD activity mainly under hypersaline conditions.     

Toxicity of atrazine and chlorsulfuron to algae

Sensitivity of three algal species, Chlorella vulgaris, Scenedesmus acutus and Pseudanabaena galeata to herbicides atrazine and chlorsulfuron was studied using single species toxicity tests. Organisms were exposed to different concentrations of these herbicides and the algal growth was measured by turbidity at 750 nm. Atrazine appeared to be the most inhibitory to algae growth. 96 hr E_bC₅₀ of atrazine was: 1.3, 0.014, 0.014 mg/1 for C. saccharophila, S. acutus and P. galeata, respectively and 96 hr E_bC₅₀ of chlorsulfuron was 74.5 mg/1 for C.saccharophila, 0.19 mg/1 for S. acutus and 21.1 mg/1 for P. galeata     

The mechanism of calcification and its relation to photosynthesis and respiration in the scleractinian coral <Emphasis Type="Italic"> Galaxea fascicularis</Emphasis>

The mechanism of calcification and its relation to photosynthesis and respiration were studied with Ca²⁺, pH and O₂ microsensors using the scleractinian coral Galaxea fascicularis. Gross photosynthesis (Pg), net photosynthesis (Pn) and dark respiration (DR) were measured on the surface of the coral. Light respiration (LR) was calculated from the difference between Pg and Pn. Pg was about seven times higher than Pn; thus, respiration consumes most of the O₂ produced by the algal symbiont's photosynthesis. The respiration rate in light was ca. 12 times higher than in the dark. The coupled Pg and LR caused an intense internal carbon and O₂ cycling. The resultant product of this cycle is metabolic energy (ATP). The measured ATP content was about 35% higher in light-incubated colonies than in dark-incubated ones. Direct measurements of Ca²⁺ and pH were made on the outer surface of the polyp, inside its coelenteron and under the calicoblastic layer. The effects on Ca²⁺ and pH dynamics of switching on and off the light were followed in these three compartments. Ca²⁺ concentrations decreased in light on the surface of the polyp and in the coelenteron. They increased when the light was switched off. The opposite effect was observed under the calicoblastic layer. In light, the level of Ca²⁺ was lower on the polyp surface than in the surrounding seawater, and even lower inside the coelenteron. The concentration of calcium under the calicoblastic layer was about 0.6 mM higher than in the surrounding seawater. Thus Ca²⁺ can diffuse from seawater to the coelenteron, but metabolic energy is needed for its transport across the calicoblastic layer to the skeleton. The pH under the calicoblastic layer was more alkaline compared with the polyp surface and inside the coelenteron. This rise in pH increased the supersaturation of aragonite from 3.2 in the dark to 25 in the light, and brought about more rapid precipitation of CaCO₃. When ruthenium red was added, Ca²⁺ and pH dynamics were inhibited under the calicoblastic layer. Ruthenium red is a specific inhibitor of Ca-ATPase. The results indicated that Ca-ATPase transports Ca²⁺ across the calicoblastic layer to the skeleton in exchange for H⁺. Addition of dichlorophenyldimethylurea completely inhibited photosynthesis. The calcium dynamics under the calicoblastic layer continued; however, the process was less regular. Initial rates were maintained. We conclude that light and not energy generation triggers calcium uptake; however, energy is also needed.