Green Alga Dunaliella Tertiolecta Research Articles

Cytotoxicity effects of water dispersible oxidized multiwalled carbon nanotubes on marine alga, Dunaliella tertiolecta

The multiwalled carbon nanotubes (MWNTs) are novel materials with many potential applications. The ecotoxicity of these materials is not well studied, but it is essential for environmental impact assessments. In this study a commercially available MWNT material was carboxylated by microwave assisted acid oxidation. This functionalized MWNT (f-MWNT) material was examined for toxicity effects using unicellular marine green alga Dunaliella tertiolecta. D. tertiolecta was exposed to f-MWNT which had been pre-equilibrated with culture media for 24 h. Substantial growth lag phase was observed at 5 and 10 mg L −1 f-MWNT, and the resulting 50% effective concentration (EC50) on 96-h growth was 0.82 ± 0.08 mg L −1. During mid-exponential growth phase cytotoxicity was evidenced at 10 mg L −1 f-MWNT in 36% reduction in exponential growth rate, 88 mV more positive glutathione redox potential (indicative of oxidative stress), 5% and 22% reduction in photosystem II (PSII) quantum yield and functional cross section respectively, all relative to the control cultures. However, when the large f-MWNT aggregates in the media with 10 mg L −1 f-MWNT were removed by 0.2 μm filtration, D. tertiolecta did not show significant cytotoxicity effects in any of the above parameters. This suggests that the cytotoxicity effects originated predominately from the large f-MWNT aggregates. Analysis of the f-MWNT aggregation dynamics suggests active interaction between f-MWNT and algal cells or cell metabolites that promoted f-MWNT aggregation formation. The f-MWNT particles were also found absorbed on algal cell surface. The direct contact between f-MWNT and cell surface was likely responsible for reduced PSII functional cross section and oxidative stress during exponential growth.

Assessing sediment quality in Spanish ports using a green alga bioassay

Coastal zones are under environmental pressure due to human activities, and ports are the areas that probably present the highest levels of contaminants in their sediments. In the present study we have combined chemical data and biological effects to determine the sediment quality of six Spanish ports. Trace metals and organic contaminants have been analyzed, and an acute bioassay was carried out in sediment elutriate using the unicellular green alga Dunaliella tertiolecta. The toxicological parameter employed was EC50, which was estimated after exposure to different concentrations of elutriates during 72 h. The development of this alga may be affected when there is a xenobiotic in the environment, and growth inhibition can be quantified and linked to the levels of contaminants in the sediment in order to determine its quality. The results showed that the metals (Cd, Cr, Hg, and Zn) and organic contaminants (PAHs and PCBs) bound to the sediments reduced the normal growth of the alga, but no alterations were detected due to the presence of Cu. The main disadvantage observed was the hormesis produced by the presence of high levels of organic material in the sediment that might hide the toxicity of xenobiotics.

Effects of sonication and advanced chemical oxidants on the unicellular green alga Dunaliella tertiolecta and cysts, larvae and adults of the brine shrimp Artemia salina: A prospective treatment to eradicate invasive organisms from ballast water

Uptake and release of ship-borne ballast water is a major factor contributing to introductions of aquatic phytoplankton and invasive macroinvertebrates. Some invasive unicellular algae can cause harmful algal blooms and produce toxins that build up in food chains. Moreover, to date, few studies have compared the efficacy of ballast water treatments against different life history phases of aquatic macroinvertebrates. In the present study, the unicellular green alga Dunaliella tertiolecta, and three discrete life history phases of the brine shrimp Artemia salina, were independently used as model organisms to study the efficacy of sonication as well as the advanced oxidants, hydrogen peroxide and ozone, as potential ballast water treatments. Algal cells and brine shrimp cysts, nauplii, and adults were subjected to individual and combined treatments of sonication and advanced oxidants. Combined rather than individual treatments consistently yielded the highest levels of mortality in algal cells (100% over a 2 min exposure) and in brine shrimp (100% and 95% for larvae and adults, respectively, over a 2 min exposure). In contrast, mortality levels in brine shrimp cysts (66% over 2 min; increased to 92% over a 20 min exposure) were moderately high but consistently lower than that detected for larval or adult shrimp. Our results indicate that a combination of sonication and advanced chemical oxidants may be a promising method to eradicate aquatic unicellular algae and macroinvertebrates in ballast water.

Evaluation of single and joint toxic effects of two antifouling biocides, their main metabolites and copper using phytoplankton bioassays

Single and joint effects of two antifouling booster biocides, irgarol 1051 (2-methylthio-4- tert-butylamino-6-cyclopropylamino- s-triazine) and diuron (1-(3,4 dichlorophenyl)-3,3 dimethyl urea), their metabolites, M1 (2-methylthio-4- tert-butylamino- s-triazine), DCPMU (1-(3,4-dichlorophenyl)-3 methyl urea), DCPU (1-(3,4 dichlorophenyl urea) and DCA (3,4-dichloroaniline), respectively, as well as copper were examined. Two phytoplanktonic microorganisms, the green alga Dunaliella tertiolecta and the diatom Navicula forcipata were exposed to various concentrations of the aforementioned compounds both alone and in binary mixtures during a period of 96 h. Estimation of EC 50 values was performed by daily cell number counting of the tested microorganisms. The toxicity of the six compounds and the metal, applied singly, was found to be, in decreasing order, irgarol 1051 > diuron > M1 > DCPMU > DCA > Cu > DCPU and irgarol 1051 > diuron > M1 > DCA for the green alga and the diatom, respectively. Diatoms were found to be more sensitive in the presence of all the tested compounds, except diuron. Co-existence of irgarol 1051 and M1 revealed additive effects on both microorganisms. Same results were observed owing to the joint action of copper with either irgarol 1051 or M1 for almost all the examined mixtures. Combined effects of diuron with its metabolites DCPMU and DCA resulted in synergism in almost all cases, for both species of phytoplankton. On the contrary, antagonistic effects were observed owing to the joint action of copper with either diuron or one of its metabolites.

Removing UV‐A and UV‐C Radiation from UV‐B Fluorescent Lamp Emissions. Differences in the Inhibition of Photosynthesis in the Marine Alga Dunaliella tertiolecta Using Chromate Versus Cellulose Acetate‐Polyester Filters¶

ABSTRACTUltraviolet‐B (UV‐B; 280‐320 nm)‐emitting lamps unavoidably emit ultraviolet‐A (UV‐A; 320‐400 nm) and ultraviolet‐C (UV‐C; < 280 nm) radiation. Short‐wavelength‐blocking filters are generally used to limit the wave bands of UV under investigation. The widespread use of such filters means that all exposures to UV‐B radiation will have a significant UV‐A component. Therefore, the physiological effects unique to UV‐B exposure are difficult to clearly isolate. This study presents a method to remove the UV‐A and UV‐C “contamination” using a liquid potassium chromate (K2CrO4) filter, thus allowing more direct assessment of the effects of UV‐B exposure. Cultures of the green marine alga Dunaliella tertiolecta were grown in the absence of UV radiation. Sunlamps supplied the UV radiation for a 24 h exposure (solar radiation was not used in this study). The UV radiation was filtered either by the standard method (i.e. cellulose acetate (CA) with polyester = Mylar controls) or by a liquid filter of potassium chromate. Photosynthetic responses were compared. Major decreases in the ratio of variable to maximal fluorescence in dark‐adapted cells and photosynthetic capacity were observed in CA‐filtered cultures, whereas no change was observed in cells exposed to the same UV‐B flux with the UV‐A removed by K2CrO4. The use of a CA filter with a Mylar control does not link results unequivocally to UV‐B radiation. Such results should be interpreted with caution.

MOLECULAR CHARACTERIZATION OF THE ASSIMILATORY NITRATE REDUCTASE GENE AND ITS EXPRESSION IN THE MARINE GREEN ALGA DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

Nitrate is used as a nutrient for growth by many organisms through the nitrate assimilation pathway. The key enzyme involved in nitrate assimilation is nitrate reductase (NR). Transcriptional regulation of NR genes has been studied in various phototrophic eukaryotes from freshwater or terrestrial habitats. Here, we describe the first NR gene from a marine phytoplankton, the green alga Dunaliella tertiolecta Butcher. Its sequence is very similar to that of the other green algae, but its intron structure and transcriptional regulation differ significantly. A partial genomic NR gene fragment was cloned using direct PCR amplification with degenerate primers, and rapid amplification of cDNA ends was performed to obtain a complete NR gene from a cDNA of D. tertiolecta. The complete NR gene of D. tertiolecta is 2.7 kb in size and is similar at the amino acid level to the NRs from freshwater green algae Chlorella vulgaris (50.6%), Chlamydomonas reinhardtii (58.4%), and Volvox carteri (59.4%). Transcriptional regulation of D. tertiolecta NR was examined in response to different nitrogen sources and during the diel cycle. Dunaliella tertiolecta NR transcript was induced by nitrate and repressed by ammonium. In addition, transcription was not induced under nitrogen depletion. Induction of NR transcript responded to the diel cycle, and transcript levels were maximized within an hour after the beginning of the light period. The induction and repression of NR transcript were much slower than reported in freshwater green algae, which may be related to the size of internal nitrogen pools.

Growth, development and condition of Dendraster excentricus (Eschscholtz) larvae reared on natural and laboratory diets

Feeding invertebrate larvae may be food limited while developing in the ocean. If they are, then their time in the plankton is prolonged, which likely increases mortality. Food limitation could be due to the quantity and/or quality of the food available. In an effort to answer how food type influences larval nutrition, we compared growth, development and lipid deposition for Dendraster excentricus larvae reared in natural seawater from two depths (1 and 20 m) and in filtered seawater on a monoculture laboratory diet of 6 cells L � 1 of the green alga Dunaliella tertiolecta (Butcher). Five days post-fertilization, larvae reared on the laboratory diet had developed to the latest stage, were the largest and had lipid deposits. Larvae reared on natural surface water were intermediate in size and developmental stage, and larvae reared in the water from 20 m depth were the smallest and developed the slowest. This trend continued at 8 days post-fertilization when surface water diet larvae were similar in size to laboratory diet larvae, but their juvenile rudiments were significantly smaller. To assess food availability in each food treatment, we compared the concentration of chlorophyll (Chl) a, b and c in natural seawater from each depth and in D. tertiolecta culture in filtered seawater. Natural seawater collected from the surface had the highest concentration of Chl a and c, whereas Chl b was not significantly different between treatments. Increased Chl concentrations in the surface water are likely due to higher concentrations of diatoms and dinoflagellates, which are typically not high-quality food items for echinoid larvae. Our results support a hypothesis that echinoid larvae in the water column may be limited by food quality.

Removing UV-A and UV-C Radiation from UV-B Fluorescent Lamp Emissions. Differences in the Inhibition of Photosynthesis in the Marine Alga Dunaliella tertiolecta Using Chromate Versus Cellulose Acetate–Polyester Filters

Ultraviolet-B (UV-B; 280–320 nm)–emitting lamps unavoidably emit ultraviolet-A (UV-A; 320–400 nm) and ultraviolet-C (UV-C; <280 nm) radiation. Short-wavelength–blocking filters are generally used to limit the wave bands of UV under investigation. The widespread use of such filters means that all exposures to UV-B radiation will have a significant UV-A component. Therefore, the physiological effects unique to UV-B exposure are difficult to clearly isolate. This study presents a method to remove the UV-A and UV-C “contamination” using a liquid potassium chromate (K2CrO4) filter, thus allowing more direct assessment of the effects of UV-B exposure. Cultures of the green marine alga Dunaliella tertiolecta were grown in the absence of UV radiation. Sunlamps supplied the UV radiation for a 24 h exposure (solar radiation was not used in this study). The UV radiation was filtered either by the standard method (i.e. cellulose acetate (CA) with polyester = Mylar controls) or by a liquid filter of potassium chromate. Photosynthetic responses were compared. Major decreases in the ratio of variable to maximal fluorescence in dark-adapted cells and photosynthetic capacity were observed in CA-filtered cultures, whereas no change was observed in cells exposed to the same UV-B flux with the UV-A removed by K2CrO4. The use of a CA filter with a Mylar control does not link results unequivocally to UV-B radiation. Such results should be interpreted with caution.

Removing UV-A and UV-C radiation from UV-B fluorescent lamp emissions. Differences in the inhibition of photosynthesis in the marine alga Dunaliella tertiolecta using chromate versus cellulose acetate-polyester filters.

Ultraviolet-B (UV-B; 280-320 nm)-emitting lamps unavoidably emit ultraviolet-A (UV-A; 320-400 nm) and ultraviolet-C (UV-C; <280 nm) radiation. Short-wavelength-blocking filters are generally used to limit the wave bands of UV under investigation. The widespread use of such filters means that all exposures to UV-B radiation will have a significant UV-A component. Therefore, the physiological effects unique to UV-B exposure are difficult to clearly isolate. This study presents a method to remove the UV-A and UV-C "contamination" using a liquid potassium chromate (K(2)CrO(4)) filter, thus allowing more direct assessment of the effects of UV-B exposure. Cultures of the green marine alga Dunaliella tertiolecta were grown in the absence of UV radiation. Sunlamps supplied the UV radiation for a 24 h exposure (solar radiation was not used in this study). The UV radiation was filtered either by the standard method (i.e. cellulose acetate (CA) with polyester = Mylar controls) or by a liquid filter of potassium chromate. Photosynthetic responses were compared. Major decreases in the ratio of variable to maximal fluorescence in dark-adapted cells and photosynthetic capacity were observed in CA-filtered cultures, whereas no change was observed in cells exposed to the same UV-B flux with the UV-A removed by K(2)CrO(4). The use of a CA filter with a Mylar control does not link results unequivocally to UV-B radiation. Such results should be interpreted with caution.

Euplotes magnicirratus (Ciliophora, Hypotrichia) depends on its bacterial endosymbiont 'Candidatus Devosia euplotis' for food digestion

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 36:19-28 (2004) - doi:10.3354/ame036019 Euplotes magnicirratus (Ciliophora, Hypotrichia) depends on its bacterial endosymbiont 'Candidatus Devosia euplotis¹ for food digestion Claudia Vannini, Angela Schena, Franco Verni, Giovanna Rosati* Dipartimento di Etologia, Ecologia ed Evoluzione, Università di Pisa, Italy *Corresponding author. Email: rosatig@deee.unipi.it ABSTRACT: A symbiotic relationship between the marine ciliate Euplotes magnicirratus and an alpha-proteobacterium has recently been described. The bacterial symbiont, identified by molecular analysis as a new species of the genus Devosia, is referred to with the provisional name ŒCandidatus Devosia euplotis¹. This association is constant (it was found in different ciliate strains sampled in different geographical regions), and durable (it persisted in laboratory conditions for years). The physiological significance of this association was investigated through antibiotically produced aposymbiotic E. magnicirratus and attempts to grow the endosymbionts outside their host. Aposymbiotic protozoa completely lost the ability to digest the green alga Dunaliella tertiolecta, their usual food in laboratory conditions, and died. An investigation into the different steps of the digestive process showed that acidification of the digestive vacuoles occurred normally in both symbiotic and aposymbiotic ciliates, but that subsequent activation of acid phosphatase did not occur in aposymbiotic cells. Therefore, the ciliate depends on the symbiont for digestion of its green algal food and, as a consequence, for its survival. Attempts to grow bacterial endosymbionts on diluted culture media and on ciliate homogenate were unsuccessful. The results indicate that this represents a new type of symbiosis between prokaryotes and ciliates, which is mutualistic, and most likely obligatory for both partners. KEY WORDS: Alpha-proteobacteria · Ciliates · Devosia · Digestive process · Euplotes · Lysis · Symbiosis Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 36, No. 1. Online publication date: June 24, 2004 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2004 Inter-Research.

Mitochondrial NDP kinase from Dunaliella tertiolecta (Chlorophyceae, Chlorophyta)

SUMMARY A cDNA ( DtNDK1 ) encoding a nucleoside diphosphate(NDP) kinase with a putative mitochondrial targetingsignal sequence was previously isolated from the halo-tolerant green alga Dunaliella tertiolecta . Whenexpressed in Saccharomyces cerevisiae , the processedDtNDK1 enzyme was specifically localized to mito-chondria. The present study reports several biochemi-cal characteristics of the mitochondrial NDP kinasefrom D. tertiolecta . The mature protein was expressedas either N- or C-terminal hexahistidine-tagged proteinand purified to homogeneity by affinity chromato-graphy. Native gel electrophoresis and sedimentationvelocity in sucrose density gradients showed that theactive enzyme consisted of a hexamer. The enzyme,with a pH optimum of 7, showed the highest specificityto dCDP ( K m = 50 µ mol/L) and the highest turnovertowards the synthesis of UTP (up to 140-fold higher).The present study also provides evidence that purifiedDtNDK1 proteins are capable of transferring a phos-phate group to another protein.Key words:

Photoacclimation involves modulation of the photosynthetic oxygen-evolving reactions in Dunaliella tertiolecta and Phaeodactylum tricornutum.

Net energy accumulation by marine microalgae at very low photon fluxes involves modulation of several attributes related to both the growth and photosynthetic physiology of these organisms. Here we studied flash-induced oscillatory patterns in oxygen evolution by previously dark-adapted cells of the green alga Dunaliella tertiolecta (Butcher) and the diatom Phaeodactylum tricornutum (Bohlin). The activity of the oxygen-evolving complex was found to be species-specific and influenced by photoacclimation. Results from measurements of oxygen flash yield obtained for these organisms grown under light-saturating conditions are directly comparable to those previously reported in the literature for other microalgae and higher plants. However, similar measurements on cells grown in low-light and/or light-starved conditions indicate an increased level of backward transitions (double misses) leading to the formation of super-reduced states (i.e. S-1 and S-2). Thus, in this communication, we present the first evidence that super-reduced states can be generated in vivo and speculate, on how they may be physiologically important.

NITROGEN LIMITATION IN DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE) LEADS TO INCREASED SUSCEPTIBILITY TO DAMAGE BY ULTRAVIOLET‐B RADIATION BUT ALSO INCREASED REPAIR CAPACITY1

Chl fluorescence was used to measure the photosynthetic capacity of the green alga Dunaliella tertiolecta in order to investigate interactions between susceptibility to acute UV‐B radiation (UVBR, 280–320 nm) exposure and decreased nitrogen availability. Under UVBR exposure the decline in the fluorescence parameters Fv/Fm (the maximum effective quantum yield ΦPSIIe‐max) and Fv′/Fm′ (the operational quantum yield of PSII, ΦPSIIe) were enhanced with higher UVBR fluxes, with the data well described by the Kok model, inferring that a dynamic balance existed between damage and repair with the repair proportional to the pool size of inactivated targets. When UVBR exposure was coupled with nitrogen limitation, the inhibition of photosynthesis was intensified. Under the more severely N‐limited conditions, the damage rate increased. Unexpectedly, repair rates were also stimulated under N‐limited conditions, although this was insufficient to counteract the increase in damage, so the overall effect of N limitation was an enhancement of UVBR‐induced inhibition of photosynthesis.

Photosynthetic efficiency of Dunaliella tertiolecta under short light/dark cycles

Inside photobioreactors algae are exposed to light/dark fluctuations. In this study the marine green alga Dunaliella tertiolecta was cultivated under short light/dark cycles of 3/3 s, 94/94 ms and 31/156 ms as found in medium and short light-path reactors. The photon flux density (PFD) during the light period was 440–455 μmol m −2 s −1 and, under the 31/156 ms cycle only, 1025 μmol m −2 s −1. The photosynthetic efficiency was determined and expressed as the biomass yield on light energy in gram protein produced per mol of photons absorbed. The yield under the 94/94 ms cycle was higher than the yield under continuous light of 440–455 μmol m −2 s −1. Apparently a light integration effect occurs under the 94/94 ms cycle together with an increase of the photosynthetic efficiency. On the contrary, at the 3/3 s cycle the efficiency decreased. Also under the 31/156 ms cycle, with 1025 μmol m −2 s −1 in the light period, the yield was lower than under continuous light. The results obtained under the 31/156 ms light/dark cycle are discussed with respect to the performance of short light-path flat panel photobioreactors operated at high biomass densities.

H 2 production from algal biomass by a mixed culture of Rhodobium marinum A-501 and Lactobacillus amylovorus

To produce hydrogen from starch accumulated in an algal biomass, we used a mixed culture of the lactic acid bacterium, Lactobacillus amylovorus, and the photosynthetic bacterium, Rhodobium marinum A-501. In this system L. amylovorus, which possesses amylase activity, utilized algal starch for lactic acid production, and R. marinum A-501 produced hydrogen in the presence of light using lactic acid as an electron donor. Algal starch accumulated in the marine green alga Dunaliella tertiolecta, and the freshwater green alga Chlamydomonas reinhardtii, was more suitable for lactic acid fermentation by L. amylovorus than an authentic starch sample. Consequently, the yields of hydrogen obtained from starch contained in D. tertiolecta and C. reinhardtii were 61% and 52%, respectively, in the mixed culture of L. amylovorus and R. marinum A-501. These values were markedly superior to those obtained using a mixed culture of Vibrio fluvialis T-522 and R. marinum A-501 described previously. The yield and production rate of hydrogen by R. marinum A-501 from the lactic acid fermentates were higher than from authentic lactic acid, suggesting that the fermentates contain a factor(s) which promotes H 2 production by this bacterium.

H2 Production from Algal Biomass by a Mixed Culture of Rhodobium marinum A-501 and Lactobacillus amylovorus.

To produce hydrogen from starch accumulated in an algal biomass, we used a mixed culture of the lactic acid bacterium, Lactobacillus amylovorus, and the photosynthetic bacterium, Rhodobium marinum A-501. In this system L. amylovorus, which possesses amylase activity, utilized algal starch for lactic acid production, and R. marinum A-501 produced hydrogen in the presence of light using lactic acid as an electron donor. Algal starch accumulated in the marine green alga Dunaliella tertiolecta, and the freshwater green alga Chlamydomonas reinhardtii, was more suitable for lactic acid fermentation by L. amylovorus than an authentic starch sample. Consequently, the yields of hydrogen obtained from starch contained in D. tertiolecta and C. reinhardtii were 61% and 52%, respectively, in the mixed culture of L. amylovorus and R. marinum A-501. These values were markedly superior to those obtained using a mixed culture of Vibrio fluvialis T-522 and R. marinum A-501 described previously. The yield and production rate of hydrogen by R. marinum A-501 from the lactic acid fermentates were higher than from authentic lactic acid, suggesting that the fermentates contain a factor(s) which promotes H2 production by this bacterium.

Laboratory bioaccumulation of copper, lead and selenium in the marine alga dunaliella tertiolecta metal pair situation

Individual and combined effects on the bioaccumulation of three heavy metals; namely, copper, lead and selenium, in the unicellular green alga Dunaliella tertiolecta were determined in natural sea water enriched with f/ 2 medium. Exponentially growing cells of alga were exposed to the three metals in the form of Cu(NO3)2 5H2O, Pb(NO3)2 and Na2SeO3 5H2O for 24 h. The pH effect on the bioaccumulation of each metal has been investigated. Total copper and lead concentrations were measured by atomic absorption spectrophotometer, whereas total selenium concentration was measured by spectrofluorometer. The bioaccumulation of metals occurred in a dose‐dependent manner. When pH decreased, the bioaccumulation of copper decreased significantly, but the bioaccumulation of lead and selenium almost stayed constant. The presence of copper interacted antagonistically with lead in various bimetallic combinations. Lead showed no effect on the bioaccumulation of copper. Coexistence of selenium with lead and copper showed antagonistic behaviour on the growth of alga microscopically.

Temperature dependence of nitrate reductase activity in marine phytoplankton: biochemical analysis and ecological implications

The temperature dependence of NADH:NR activity was examined in several marine phytoplankton species and vascular plants. These species inhabit divergent thermal environments, including the chromophytes Skeletonema costatum (12–15° C), Skeletonema tropicum (18–25° C), Thalassiosira antarctica (−2 to 4° C), and Phaeocystis antarctica (−2 to 4° C), the green alga Dunaliella tertiolecta (14–28° C), and the vascular plants Cucurbita maxima (20–35° C) and Zea mays (20–25° C). Despite the difference in growth habitats, similar temperature response curves were observed among the chromophytic phytoplankton, with temperatures optimal for NR activity being between 10–20° C. In contrast, the chlorophyll b‐containing alga and vascular plants exhibited optimal temperatures for NR activity above 30° C. Such dramatic differences in NR thermal characteristics from the two taxonomic groups reflect a divergence in NR structure that may be associated with the evolutionary diversification of chromophytes and chlorophytes. Further, it suggests a potential contribution of the thermal performance of NR to the geographic distributions, seasonal abundance patterns, and species composition of phytoplankton communities. NR partial activities, which assess the individual functions of Mo‐pterin and FAD domains, were evaluated on NR purified from S. costatum to determine the possible causes for high temperature (&gt;20° C) inactivation of NR from chromophytes. It was found that the FAD domain and electron transport among redox centers were sensitive to elevated temperatures. S. costatum cells grown at 5, 15, and 25° C exhibited an identical optimal temperature (15° C) for NADH:NR activity, whereas the maximal NR activity and NR protein levels differed and were positively correlated with growth temperature and growth rate. These findings demonstrate that thermal acclimation of NO3− reduction capacity is largely at the level of NR protein expression. The consequences of these features on NO3− utilization are discussed.

Changes in chlorophyll fluorescence during exposure of Dunaliella tertiolecta to UV radiation indicate a dynamic interaction between damage and repair processes.

Photosynthesis in the green alga Dunaliella tertiolecta, as measured by chlorophyll fluorescence, is inhibited by ultraviolet radiation and specifically, under the conditions used, by UVB radiation (UVBR). The decline in the fluorescence parameters F(v)/F(m) and DeltaF/F'(m) under constant UVBR is a first-order function of time of exposure. The data are well-described by the Kok (1956) model, which assumes a dynamic interaction between damage and repair, with repair being proportional to the pool size of inactivated targets. The pattern of photoinhibition is also consistent with the Kok model, in that it shows an initial, approximately linear phase which is time-dependent (reciprocity holds), a transition phase and then an asymptotic phase, representing an equilibrium between damage and repair, which is determined by UVBR fluence rate (reciprocity fails). Photoinhibition in the presence of lincomycin, a protein synthesis inhibitor, is consistent with the cessation of repair processes and, under these conditions, photoinhibition is proportional to exposure time.

Effects of Prior Exposure to Petroleum Hydrocarbon Contamination during Brooding on the Subsequent Larval Development of the Brachyuran Crab Hemigrapsus oregonensis

Larvae of the brachyuran crab Hemigrapsus oregonensis were raised in the laboratory from broods obtained from egg-bearing females collected at a site previously contaminated by a spill of crude petroleum hydrocarbons and from a site not recently contaminated. Larvae from both sites were raised throughout development on 2 diets of the rotifer Brachionus plicatilis, one in which the rotifer was cultured on the green alga Dunaliella tertiolecta, the other cultured on the brown alga Isochrysis galbana. Percentage mortality per stage for larvae from the contaminated site was equal to or lower than for larvae from the clean site. There was no difference in duration of zoeal development nor for megalopal weight for larvae from either site on either diet. Larvae raised on rotifers fed Dunaliella showed higher mortality during the fifth zoeal stage, longer zoeal duration for stages II-V, and lower megalopal weight than did those raised on rotifers fed Isochrysis. Results indicate that previous exposure to petroleum hydrocarbon contamination during brooding has no effect on subsequent zoeal development when larvae are not directly exposed to contamination. Differences in larval response to diet demonstrate that the nutritional value of heterotrophic prey will depend upon what the prey has previously fed upon, either in the laboratory or in nature. Marine organisms may be exposed to petroleum hydrocarbon contamination in coastal waters due to transport, exploration and development of petroleum resources, and episodes of mechanical and industrial failure (Burger and Gochfeld, 1992). Crabs that occupy shallow subtidal and intertidal habitats may be particularly susceptible to hydrocarbon exposure due to their sedentary life style that includes burrowing into the mud or hid