Ingestion of the cyanobacterium Trichodesmium spp. by pelagic harpacticoid copepods Macrosetella,Miracia and Oculosetella

Trichodesmium is a filamentous, colonial nitrogen fixing cyanobacteria, ubiquitous in tropical and subtropical regions of the world's oceans. Trichodesmium fixes atmospheric nitrogen and can comprise a significant fraction of total primary production in oceanic surface waters. Therefore, the consumption and fate of Trichodesmium has important consequences for understanding carbon and nitrogen cycling in the open ocean. The pelagic harpacticoid copepod Macrosetella gracilis uses Trichodesmium not only as a physical substrate for juvenile development, but also as a food source. Several different types of pelagic copepods (including several species of calanoids, harpacticoids and a poecilostomatoid species) were tested for ingestion of Trichodesmium by labelling the cyanobacteria with ¹⁴C. Only the pelagic harpacticoids ingested Trichodesmium. Here we report the first grazing rates based on ¹⁴C-uptake measurements for Macrosetella gracilis (0.173 µg C copepod^–1 h^–1), and the first quantitative measurements of both Miracia efferata (0.402 µg C copepod^–1 h^–1) and Oculosetella gracilis (0.126 µg C copepod^–1 h^–1) ingesting this cyanobacteria. Ingestion rates of M. gracilis and M. efferata on the two different species of Trichodesmium, T. thiebautii and T. erythraeum, as well as the two different colonial morphologies of T. thiebautii, spherical-shaped (puffs) and fusiform (tufts), were also compared. Both Miracia and Macrosetella had higher ingestion rates on the puff colonies than the tuft colonies of T. thiebautii.. Both also had higher ingestion rates of T. erythraeum than T. thiebautii. Trichodesmium thiebautii contains a previously reported neurotoxin which may be an important factor in determining trophodynamic interactions. Our results suggest that pelagic harpacticoid copepods can be quantitatively important in determining the fate of Trichodesmium carbon and nitrogen.     

Effect at the ecosystem level of elevated atmospheric CO2in an aquatic microcosm

We studied the responses of an aquatic microcosm in two different eutrophic conditions to elevated atmospheric CO₂concentration. We used microcosms, consisting of Escherichia coli(bacteria), Tetrahymena thermophila(protozoa) and Euglena gracilis(algae), in salt solution with 50 and 500 mg l^–1of proteose peptone (eutrophic and hypereutrophic conditions, respectively) under ambient and elevated CO₂(1550±100 l l^–1) conditions. The density of E. gracilisincreased significantly under elevated CO₂in both eutrophic and hypereutrophic microcosms. In the eutrophic microcosm, the other elements were not affected by elevated CO₂. In the hypereutrophic microcosm, however, the concentrations of ammonium and phosphate decreased significantly under elevated CO₂. Furthermore, the density of T. thermophilawas maintained in higher level than that in the microcosm with ambient CO₂and the density of E. coliwas decreased by CO₂enrichment. Calculating the carbon biomasses of T. thermophilaand E. colifrom their densities, the changes in their biomasses by CO₂enrichment were little as compared with large increase of E. graciliscarbon biomass converted from chlorophyll a. From the responses to elevated CO₂in the subsystems of the hypereutrophic microcosm consisting of either one or two species, the increase of E. graciliswas a direct effect of elevated CO₂, whereas the changes in the density of E. coliand T. thermophilaand the decreases in the concentration of ammonium and phosphate are considered to be indirect effects rather than direct effects of elevated CO₂. The indirect effects of elevated CO₂were prominent in the hypereutrophic microcosm.     

Effects of acidity on the growth of two Euglena species

Our study separates the effects of elevated protons (at pH <3) and elevated metals (Al, Cd, Cu, Fe, Ni, Zn) on the growth of E. mutabilis Schmitz, a pioneering phototroph in acid mine drainage (AMD) and E. gracilis Klebs, a closely-related species rarely found in severely AMD-impacted sites. Both species were acid tolerant, growing optimally at pH 2.5–7. At pH values typical of AMD (pH 2.5–4) in the absence of elevated metals, E. gracilis outcompeted E. mutabilis (growth rates of 1.0 and 0.8 div d^–1, respectively). Relative metal toxicities were evaluated based on the Effective Exposure causing 50% growth reduction (= EE50). With total metal additions similar to AMD levels, E. mutabilis demonstrated significantly greater tolerance to all metals, except Cu. E. gracilis showed two-fold higher tolerance to Cu²⁺ than E. mutabilis (EE50 of 91.6 vs. 45.7 pmol cell^–1). The EE50 for Zn²⁺ was similar for both species (368 pmol cell^–1 for E. gracilis and 423 pmol cell^–1 for E. mutabilis). With Cd and Ni, E. mutabilis tolerated an order of magnitude higher exposure than E. gracilis(EE50 of 1.6 vs. 0.2 pmol Cd²⁺ cell^–1; EE50 of 942 vs. 87 pmol Ni²⁺ cell^–1). Al and Fe were tolerated at high total metal concentrations (up to 100 mM) by E. mutabilis, but toxicity was evident with E. gracilisat much lower levels. E. mutabilis grew at double the Al³⁺ exposure tolerated by E. gracilis (EE50 of 398 vs. 188 pmol Al³⁺ cell^–1). There was an 18-fold difference in Fe tolerance levels between E. mutabilis and E. gracilis with EE50s of 8773 and 502 pmol Fe²⁺ cell^–1, respectively. We conclude that differential metal tolerance, particularly to Fe²⁺, accounts for the mutually exclusive distribution of E. gracilis and E. mutabilis in AMD-impacted habitats.     

Evidence for a composite phylogenetic origin of the plastid genome of the brown alga Pylaiella littoralis (L.) Kjellm

The nucleotide sequence and the 5 flanking region of the rbcL gene coding for the large subunit of ribulose bisphosphate-1,5-carboxylase/oxygenase of Pylaiella littoralis, a brown alga, has been determined and the deduced amino-acid sequence has been compared to those of various photosynthetic and chemoautotrophic Eubacteria, of a red alga and of green plastids (Euglena gracilis, green algae and higher plants). Unlike the rbcL genes of green plastids which are more closely related to those of cyanobacteria the P. littoralis rbcL gene is more closely related to that of a -purple bacterium, as was found for the rbcS gene of another chromophytic alga [Boczar et al., Proc Natl Acad Sci USA 86: 4996–4999, 1989]. Matrix data of homology between the rbcL gene of P. littoralis and the same gene of other organisms are presented. Based on our previous report, the gene coding for the 16S rRNA from P. littoralis is closely related to that of E. gracilis (Markowicz et al., Curr Genet 14: 599–608, 1988). We suggest that the large plastid DNA molecule of P. littoralis is a phylogenetically composite genome which probably resulted from mixed endosymbiosis events, or from a horizontal transfer of DNA.     

Cryopreservation ofTetraselmis suecica cultured under different nutrients regimes

The commercially important member of the PrasinophyceaeTetraselmis suecica CCAP 66/4, which is widely used in the aquaculture industry, can be cryopreserved with levels of post-thaw viability in excess of 65%. The nutritional mode which the alga uses appears to be of secondary importance to the cryoprotectant and cooling protocol used, to maximise survival. Glycerol was the least cytotoxic and most protective of the cryoprotectants employed and a cooling rate of 5 °C min^-1 to -30 °C with a 10-minute equilibration, followed by plunging into liquid nitrogen was found to give the highest levels of post-thaw viability.     

Transient gene expression in electroporated protoplasts of Eucalyptus citriodora Hook

Protoplasts isolated from cotyledons of Eucalyptus citriodora were electroporated using a rectangular pulse, with plasmid carrying the cat gene. The levels of transient expression and protoplast viability were influenced by the voltage and pulse duration. At a field strength of 800 V cm^-1 (1000 s), a protoplast viability of 57%, and 47% conversion of ¹⁴C-chloramphenicol to its acetylated forms, were obtained. Expression levels were improved by an increase in plasmid concentration (up to 60 g ml^-1), and also by the addition of carrier DNA. Gene expression was further enhanced by the addition of 40% (w/v) PEG, in the presence of the carrier DNA, to the protoplasts after electroporation.Abbreviations BAP 6-benzylaminopurine - CAT chloramphenicol acetyltransferase - CPW 13M CPW salts medium with 13% (w/v) mannitol - DC direct current - FDA fluorescein diacetate - f. wt fresh weight - GUS -glucuronidase - K Kao (1977) - MES 2-N-morpholinoethane sulfonic acid - MS Murashige & Skoog (1962) - NAA -naphthaleneacetic acid - PVP-10 polyvinylpyrrolidone (Av MW 10,000) - TLC thin layer chromatography     

Effects of nitrogen and phosphorus on blue grama growth and mycorrhizal infection

Summary The purpose of this study was to examine the growth response of Bouteloua gracilis, with and without the vescular-arbuscular mycorrhiza (VAM), Glomus fasciculatus, to varying levels of phosphorus and nitrogen (as NH ₊ ⁴ ) and to determine whether nitrogen and phosphorus levels influence VAM establishment. Bouteloua gracilis was grown in 225 g of soil in a factorial experiment combining four levels of ammonium nitrogen (4, 30, 60, and 126 g/g), four levels of phosphorus (3, 7, 12, and 22 g/g), and with VAM spores or no spores. Bouteloua gracilis showed enhanced growth with increased nutrients over the entire range of experimental amendments. Shoot nitrogen concentration for all plants ranged from an average of 0.73% at the low amendment level to 1.61% at the high level, whereas shoot total averages ranged from 2.43 mg at the low amendment to 16.4 mg at the high amendment. Mean shoot phosphorus concentrations ranged from 0.109% at the low amendment level to 0.150% at the high amendment, while totals averaged 5.29 mg at the low amendment and 11.8 mg at the high amendment level. Infected plants were consistently smaller than uninfected plants. This reduction was significant at high nitrogen-low phosphorus, where percent infection was highest (71%). At low nitrogen levels, moderate infection (17%) was established at all phosphorus levels. No infection occurred when both nitrogen and phosphorus levels were high. The lack of a positive nutrient or biomass response to VAM establishment is contrary to most published reports, but is similar to a lack of response shown with certain grasses and other plants. It is possible that the parasitic nature of the response to infection represents the early phase of infection.     

Nucleotide sequence of cytoplasmic 5S ribosomal RNA fromEuglena gracilis

Summary The nucleotide sequence of cytoplasmic 5S ribosomal RNA fromEuglena gracilis has been determined to be: G- _A ^C -G-U-A-C-G-G-C-C-A-U-A-C-U-A-C-C-G-G-G-A-A-U-A-C-A-C-C-U-G-A-A-C-C-C-G--U-C-G-A-U-U-U-C-A-G-A-A-G-U-U-A-A-G-C-C-G-G-G-U-U-A-G-G-C-C-C-A-G-U-U-A-G-U-A-C-U-G-A-G-U-G-G-G-C-G-A-C-C-A-C-U-U-G-G-G-A-A-C-A-C-U-G-G-G-U-G-C-U-G-U-A-C-G-C-U-Up. This RNA is 119 nucleotides long and the sequence of a probable tRNA-binding site is GAUU (position 41–44 from the 5-terminus), which is the same as that of a trypanosoma species,Crithidia fasci-culata. TheEuglena 5S rRNA has a pseudouridine residue at position 38 and 3-terminus is phosphorylated. The 5S rRNA sequence ofEuglena resembles those of several other protozoa and higher animals rather than plants.On leave from Department of Zoology, Hiroshima University, Hiroshima, Japan     

Riboflavin-binding sites associated with flagella of Euglena: A candidate for blue-light photoreceptor?

The hypothesis was tested that reversible riboflavin (RF)-binding sites are part of the photoreceptor in Euglena gracilis. Published evidence shows that the phototactic stimulus — with a flavin-type action spectrum — is perceived at the paraflagellar body (PFB). Flagella with PFBs were isolated from Euglena gracilis by a combined cold and Ca²⁺ shock. Saturable binding of [¹⁴C]RF was demonstrated with such preparations, in the oxidized state as well as under reducing conditions in the presence of dithionite. Affinities for RF were high: K _D (oxidized)=0.08 M, and K _D (reduced)=0.7 M. Flavin mononucleotide and flavin adenine dinucleotide showed lower binding affinities. The in vitro RF binding per unit of protein was enriched approximately tenfold in the flagellar preparations when compared with homogenates of whole cells. The number of (reduced) binding sites per entire flagellum was determined to be in the order of 10⁶. This number is in line with published estimates of chromophores bound in or at the PFB.Abbreviations FAD flavin adenine dinucleotide - FMN flavin mononucleotide - PFB paraflagellar body - RF riboflavin This work was supported by the Deutsche Forscungsgemeinschaft.     

The occurrence of two species of <Emphasis Type="Italic">Macroramphosus</Emphasis> (Gasterosteiformes: Macroramphosidae) in Japan: morphological and ecological observations on larvae,juveniles, and adults

Earlier opinions that Macroramphosus is monotypic are refuted, with two species apparently occurring in Japan (tentatively identified as M. gracilis and M. scolopax). In postsettlement young and adults, the former is characterized by a dark slender body (vs. red-orange and deep) and short second dorsal fin spine with a smooth posterior margin (vs. long spine with a serrated margin). Food habits also differ between the two species, which are either plankton or benthos feeders. Two types of Macroramphosus larvae and juveniles occurring at the surface were recognized, one having a straight ventral body profile of the body (identified here as M. gracilis) and the other having a notch in the anal region. The dark body of postsettlement M. gracilis is considered to be a retention of the character suited to the neustonic distribution of the larval and juvenile stages, the species remaining to ca. 40mm in standard length (SL) in that habitat (vs. to ca. 12mm SL in M. scolopax).     

An in vitro oxidative stress test for determining pollutant tolerance in algae

An in vitro oxidative stress test has been developed to assess pollutant tolerance in freshwater algae using Euglena gracilis as the test organism and FeSO₄ and NaCl as the pollutants. The test evaluates free radical-mediated oxidative stress through the concomitant application of three biochemical assays: (1) the non-invasive, gas chromatographic-volatile headspace analysis of hydroxyl radicals (OH) using dimethyl-sulphoxide as a radical trap; (2) the spectroscopic determination of total antioxidant activity; (3) a fluorescent microscopy viability test. In vitro pollutant testing was devised to simulate contaminant loadings that impact urban retention ponds. E. gracilis was found to be tolerant to FeSO₄ (2–10% (w/v)) and NaCl (10–5000 ppm) as indicated by high positive viabilities (ca. 100%) and low, or no OH production, as compared to controls. Total antioxidant activity increased with increasing pollutant loading suggesting that the organism has the capacity to enhance antioxidant defence in response to pollutant stress. This in vitro test provides a new approach to monitor the effects of water quality on the biological components of urban and/or polluted aquatic ecosystems. It also has a potential application in the identification of putative algal phytoremediators.     

Eucalyptus stomata with occluded anterior chambers

Summary This paper describes variations of a mode of stomatal development already described in a species (E. orbifolia) ofEucalyptus L'Herit. (Carr andCarr, Protoplasma 96, 127, 1978) in which the outer part of the stomatal pore (ostiole) is formed by the creation of a break in the thin layer of cuticle lying over the stomatal chamber. In a number of species with a thick cuticle (e.g., E. cooperana) the process of breakthrough is different: additions to the guard cell upper thickenings extend from them as ridges, pressing the leaf cuticle outwards. Breakthrough of the cuticle occurs above the tips of these extensions. The anterior chamber is lined throughout by the extensions, which become heavily cutinized. This mode of stomatal development is typical of many other species of eucalypts, including those dealt with in this paper.In addition, inE. halophila thickenings develop on the end walls of the anterior chamber above the unusual upturned poles of the guard cells. Cutinized thickenings, pseudo-outer stomatal ledges are also formed on the upper guard cell walls. All these wall thickenings occlude the anterior chamber, leaving only a narrow passage in the form of a letter H.Similar occlusions are found inE. balladoniensis but here the thickenings are developed into the chamber from its lateral walls. InE. gracilis, and the related speciesE. celastroides andE. calycogona, less regular occluding thickenings develop principally from the lateral walls of the chamber. In addition, large pseudo-outer stomatal ledges may be formed.These phenomena are discussed in terms of the mechanism underlying the formation of the occluding thickenings and the possibility of their adaptive significance.     

Ferrous iron dependent nitric oxide production in nitrate reducing cultures of Escherichia coli

l-Lactate-driven ferric and nitrate reduction was studied in Escherichia coli E4. Ferric iron reduction activity in E. coli E4 was found to be constitutive. Contrary to nitrate, ferric iron could not be used as electron acceptor for growth. Ferric iron reductase activity of 9 nmol Fe²⁺ mg^-1 protein min^-1 could not be inhibited by inhibitors for the respiratory chain, like Rotenone, quinacrine, Actinomycin A, or potassium cyanide. Active cells and l-lactate-driven nitrate respiration in E. coli E4 leading to the production of nitrite, was reduced to about 20% of its maximum activity with 5 mM ferric iron, or to about 50% in presence of 5 mM ferrous iron. The inhibition was caused by nitric oxide formed by a purely chemical reduction of nitrite by ferrous iron. Nitric oxide was further chemically reduced by ferrous iron to nitrous oxide. With electron paramagnetic resonance spectroscopy, the presence of a free [Fe²⁺-NO] complex was shown. In presence of ferrous or ferric iron and l-lactate, nitrate was anaerobically converted to nitric oxide and nitrous oxide by the combined action of E. coli E4 and chemical reduction reactions (chemodenitrification).     

Mating type regulates the radiation-associated stimulation of reciprocal translocation events in Saccharomyces cerevisiae

Both ultraviolet (UV) and ionizing radiation were observed to stimulate mitotic, ectopic recombination between his3 recombinational substrates, generating reciprocal translocations in Saccharomyces cervisiae (yeast). The stimulation was greatest in diploid strains competent for sporulation and depends upon both the ploidy of the strain and heterozygosity at the MAT locus. The difference in levels of stimulation between MATa/MAT diploid and MAT haploid strains increases when cells are exposed to higher levels of UV radiation (sevenfold at 150 J/m²), whereas when cells are exposed to higher levels of ionizing radiation (23.4 krad), only a twofold difference is observed. When the MAT gene was introduced by DNA transformation into a MATa/mat::LEU2 ⁺ diploid, the levels of radiation-induced ectopic recombination approach those obtained in a strain that is heterozygous at MAT. Conversely, when the MATA gene was introduced by DNA transformation into a MAT haploid, no enhanced stimulation of ectopic recombination was observed when cells were irradiated with ionizing radiation but a threefold enhancement was observed when cells were irradiated with UV The increase in radiation-stimulated ectopic recombination resulting from heterozygosity at MAT correlated with greater spontaneous ectopic recombination and higher levels of viability after irradiation. We suggest that MAT functions that have been previously shown to control the level of mitotic, allelic recombination (homolog recombination) also control the level of mitotic, radiation-stimulated ectopic recombination between short dispersed repetitive sequences on non-homologous chromosomes.     

Viability of Cururbita pepo pollen: biophysical and structural data

During ageing of the short-lived pollen grains of Cucurbita pepo L., water loss was examined in relation to viability using biophysical (¹H-nuclear magnetic resonance, NMR) and cytological methods (fluorochromatic reaction test, freezefracture and scanning electron microscopy). A semi-logarithmic representation of the pollen weight loss demonstrated the complexity of the dehydration process. A the study of proton loss using ¹H-NMR indicated that two major releases water of had taken place, each with different flux rates. Pulse ¹H-NMR experiments showed the occurrene of non-exponential signal decay as a function of time, indicating the existence of different fractions of water in a pollen grain sample. These fractions leave the pollen grain at different times during pollen dehydration, and one of them (that of the so-called vital water) can be related to pollen viability. The quantity of protons giving a signal during pulse ¹H-NMR experiments was very low when the pollen grains were judged to be dead according to the fluorochromatic test. Freeze-fracture replicas of these dead pollen grains (less than 25% water content) showed that the plasma membrane had become detached from the intine surface; this ultrastructural feature might therefore be involved in the loss of pollen viability.Abbreviations A initial amplitude of the NMR signal - A₂ quantity of water charcterized by T_2-2 - A₅ quantity of water characterized by T_2–5 - FCR fluorochromatic reaction - NMR nuclear magnetic resonance - T₂ transverse relaxation time - T_2-2 T₂ measured with 2 ms between each pulse of radiofrequency - T_2–5 T₂ measured with 5 ms between each pulse of radiofrequency     

Transport of an anionic substrate by the H+/monosaccharide symport inRhodotorula gracilis: Only the protonated form of the carrier is catalytically active

Summary The yeastRhodotorula gracilis accumulated glucuronate by an H⁺/symport. The transport was electroneutral, driven by the chemical gradient of protons pH. The observed stoichiometry amounted to 1 proton per molecule glucuronate. At pH 4, the half-saturation constantK _T was at its lowest value (K _T =8mm), whereas the maximal velocityV _T reached a maximum (V _T =15 nmol/min×mg dry wt). Monosaccharides competitively inhibited the uptake of glucuronate and vice versa. Hence, the two substrates share the same transport system. The steady-state accumulation of glucuronate reflected the course of the pH gradient. It is concluded that glucuronate is transported as an anionic substrate by the protonated carrier, the driving force being the chemical gradient of the H⁺ (pH). The ternary carrier/H⁺/glc-COOO-complex is electroneutral and independent of the membrane potential. Simultaneous uptake of organic acids (acetic or propionic acid) which is also energized by the pH gradient led to a noncompetitive inhibition of glucuronate transport. Thus, manipulation of the driving force, pH, reducedV _T without affectingK _T . Kinetic and energetic arguments are presented which stronly suggest that only the protonated carrier is catalytically active inR. gracilis.     

Exploration and exploitation of soil by apple,kiwifruit, peach,Asian pear and grape roots

Measurements of root-length density (RLD) in a range of 31 apple, kiwifruit, peach, Asian pear and grape orchards were used to derive indices to describe the exploration and exploitation of rooting volumes. Orchards were of various ages and located on a range of soil types, geographic regions, management systems etc. Data were obtained from core samples of volume 1.66×10^-4 m³ randomly taken within a standard volume, determined by average planting grids, of 2 m radius centred on tree stems, and 1 m depth. Root systems were described using an exploitation index, E(), and an exploration index, E(0). E() is defined as the proportion of the soil volume which contains roots at RLD greater than or equal to some specified value, . E(0) is defined as the proportion of the soil volume which contains roots at any RLD greater than zero. These indices are dependent on sample size, as are all volumetric or soil-coring data.Estimates of E(0) for each orchard were obtained as the proportions of cores containing any RLD>O and assessed for dependence on species. Peach trees had a significantly higher value of E(0), equal to almost 1.0, compared to the other four species where E(0) was approximately 0.8 (p0.01) or less. There was also some variation with age. E(0) was lower for very young plants which had not fully occupied the sampled soil volume. Exploration indices for woody roots increased with rootstock age but otherwise did not explain large differences in E() between species for given values.For example at =0.05×10⁴ m.m^-3, E() was approximately 0.45 for peach and kiwifruit, and 0.05 for apple, Asian pear and grape, whereas at =0.5×10⁴ m.m^-3 the corresponding values were 0.1 and almost zero. Negative exponential curves relating E(), scaled by dividing by E(0), to were fitted for each of the 31 orchards. Exponents for these curves, k, were significantly smaller for kiwifruit and peaches than apples, grapes and Asian pears (p0.05), and smaller for apples than grapes and Asian pears (p0.05). A larger k implies a rapid fall-off in E() as increases. Although all five species contained zero and low RLD samples, only kiwifruit and peaches contained higher RLD values and consequently have higher mean RLD. This trend was consistent across all soils, regions, sampling dates, and plant ages.The analyses demonstrate that core sampling can give useful insights into macro-scale root-system distribution, such as the proportion of a soil volume explored and how it is exploited. If positions of core samples are noted during sampling using angular direction, depth and radial distance as spatial coordinates the method can be used to describe root-system structures.     

Biofiltering efficiency in removal of dissolved nutrients by three species of estuarine macroalgae cultivated with sea bass (Dicentrarchus labrax) waste waters 2. Ammonium

Three estuarine macroalgae (Ulva rotundata,Enteromorpha intestinalis, Gracilariagracilis) of economic potential were cultivated in the laboratory toassess their biofiltering capacities for ammonium in waste effluents from a seabass (Dicentrarchus labrax) cultivation tank. The studywasdeveloped to investigate the functioning of N nutrition of the three species.Atlow water flow (< 2 volumes d^–1) the three species strippedefficiently the ammonium dissolved in the waste water from the fish tank, withaminimum biofiltering efficiency estimate of 61% in unstarved cultures ofG. gracilis at a water flow of 2 volumesd^–1. Maximum velocity for ammonium uptake (89.0 molNH₄ ⁺ g^–1 dry wth^–1) was found in U. rotundata,whereas G. gracilis showed the highest affinity for thisnutrient. The net ammonium uptake rate was significantly affected by the waterflow, being greatest at the highest flow assayed (2 volumesd^–1). Variations of tissue N and C:N ratios during aflow-through experiment suggested that N was not limiting macroalgal growth.However, when ammonium was supplied at a flow rate of 0.5 volumesd^–1, specially in a three-stage design, the marked reductionintissue N and the biomass C:N:P ratios suggested a more general nutrientdeficiency. A significant correlation was found between growth rates and the Nbiomass gained in the cultures. The three-stage design under low water flow(0.5volumes d^–1) showed that the highest ammonium uptake rates (upto 80.9 mol NH₄ ⁺ g^–1 dry wtd^–1 in U. rotundata) were found inthe first stage, with decreasing rates in the following ones. As a result, lowincrements or even losses of total N biomass in these stages were found,suggesting that ammonium was excreted from the algae. We conclude that thesespecies present a potential ability to biofilter the ammonium dissolved inwastewater from a D. labrax cultivation tank, suggesting thatscaling up the biofiltration designs, future practises using these macroalgaemay be implemented in the local fish farms, resulting in both environmental andeconomical advantages.     

Inhibition of elongation and H+ and K+ transport by the phosphodiesterase inhibitor aminophylline in plant tissue

Aminophylline, an inhibitor of cyclic nucleotide phosphodiesterase (EC 3.1.4.17), inhibits elongation and correlated H⁺ and K⁺ transport in embryos of Haplopappus gracilis and in pea internode segments. Moreover, the drug strongly inhibits the stimulation of these processes by fusicoccin and indole-3-acetic acid and reduces passive permeability of the membrane. The possible mechanisms of action of aminophylline are discussed.Abbreviations cAMP adenosine 3:5-cyclic monophosphate - FC fusicoccin - IAA indole-3-acetic acid - MES 2-N-morpholinoethanesulfonic acid - PDE cyclic nucleotide phosphodiesterase     

The effects of FMRFamide, 5-hydroxytryptamine and phorbol esters on the heart of the mussel Geukensia demissa

Summary The ventricle of the mussel Geukensia demissa is inhibited by 5-hydroxytryptamine and excited by the molluscan neuropeptide FMRFamide. Supra-threshold doses of amide result in marked positive chronotropy and inotropy within 5–15 s. 5-Hydroxytryptamine at 10^-8 M produces diastolic arrest within 10 s. A 1-min exposure to FMRFamide (5 · 10^-8 M) results in a small increase in the cytoplasmic levels of adenosine 3,5-cyclic monophosphate; shorter or longer exposures have no effect. The cAMP content of ventricles incubated in 5 · 10^-8 M 5-hydroxytryptamine for 1 min decreases by 2.3 pmol/mg protein; longer or shorter incubations have no effect. Treatment with forskolin results in 3-or 4-fold increases in adenosine 3,5-cyclic monophosphate, but forskolin has no effect on the mechanical activity of the ventricle. The levels of inositol monophosphate, inositol 1,4-diphosphate, and inositol 1,4,5-triphosphate in tissues exposed to 5-hydroxytryptamine are not different from levels in control tissues. FMRFamide decreases the levels of these phosphoinositides by 50% or more. Lower concentrations of phorbol 12,13-diacetate (10^-8 to 10^-7 M) and phorbol 12-myristate, 13-acetate (10^-6 M) cause positive chronotropy in the isolated ventricle; higher concentrations induce systolic arrest. These results suggest that the effects of 5HT on the ventricle are not mediated by adenosine 3,5-cyclic monophosphate or inositol 1,4,5-triphosphate. The effects of FMRFamide may involve a decrease in inositol 1,4,5-triphosphate. The effects of amide may involve a decrease in inositol 1,4,5-triphosphate. The response of the ventricles to phorbol esters suggest that protein kinase C may be involved in the regulation of cardiac contractility.Abbreviations cAMP adenosine 3,5-cyclic monophosphate - DMA dimethylformamide - DMSO dimethylsulfoxide - FMRFamide Phenylalanyl-methionyl-arginyl-phenylalanylamide - 5HT 5-hydroxytryptamine - IP inositol monophosphate - IP₂ inositol 1,4-diphosphate - IP₃ inositol 1,4,5-triphosphate - PDA phorbol 12,13-diacetate - PMA phorbol 12-myristate, 13-acetate - SW sea water Present address: MSU; E.M. Center, Memphis, TN 38152, USA