The glaucocystophyte algae contain simple plasmids, in common with red and green algae and higher plants. Although these groups have been shown to be monophyletic, the phylogenetic position of the latter is uncertain. The nuclear-encoded locus <I>hemB</I>, which encodes aminolaevulinic acid dehydratase (ALAD), was chosen to examine the phylogeny of the algae. ALAD occurs in organisms as either of two generalised classes; in most eubacteria, animals and fungi the enzyme requires Zn<SUP>2+</SUP> for full activity, in plants and green algae Mg<SUP>2+</SUP> is required. A sequence motif indicates which form of the enzyme is encoded by <I>hemB. </I>Sequence information was also collected for the algae for another nuclear gene <I>GapC,</I> which encodes the cytosolic form of glyceraldehye-3-phosphate dehydrogenase, for phylogenetic analysis and subsequent comparison with the <I>hemB </I>trees. A biochemical survey of the algae was carried out for ALAD, which indicated that most algae contain a Mg-binding ALAD. However the assay was unsatisfactory for some taxa and it was not possible to determine which kind of ALAD they possess. These initial results were then supplemented with sequence data for <I>hemB </I>in a number of different algae. Full and partial sequences were obtained from glaucocystophyte, red and brown algae and where this sequence included the metal-binding site, this always indicated a Mg<SUP>2+</SUP> requirement for ALAD. The position in the trees of bacteria with a Mg-binding ALAD relative to the algae, suggests that horizontal gene transfer may have been the mechanism by which plants and algae obtained a Mg-binding ALAD.

Tropical reefs, constructed during the late Palaeozoic icehouse climate, suffered high amplitude, high frequency sea level changes (Gondwanan glaciation). Rare three-dimensional outcrops of Virgilian (Pennsylvanian) and Wolfcampian (Early Permian) reefs occur in the Hueco Mountains, Texas. The reefs form part of a highly cyclical carbonate platform succession that suffered repeated emergence. The reefs are dominated by platy 'phylloid algae', these algae may belong to either Rhodophyta or Chlorophyta. The erect, recumbent or cyathiform genus <I>Eugonophyllum</I> is interpreted as belonging to the green algal family Halimedaceae. <I>Eugonophyllum </I>is the dominant reef building alga in the area studied. The prostrate phylloid alga <I>Archaeolithophyllum</I> is interpreted as belonging to the red algal family Corallinaceae. <I>Archaeolithophyllum</I> does not occur in the reefs, but forms extensive biostromes. The dominant constructional mechanism for reef formation has previously been regarded as sediment baffling and trapping, mainly by erect phylloid algae. Analysis of reef ecology clearly shows that these algae were in fact capable of forming a framework, to which considerable stability was added by secondary encrusting organisms such as the problematica <I>Tubiphytes </I>(or <I>Shamovella</I>) and <I>Archaeolithoporella. </I>Complex, multiple encrustations (both <I>in-vivo</I> and <I>post-mortem</I>) of these organisms were a fundamental element of reef construction. The effect of diagenesis on the phylloid algae and <I>Tubiphytes </I>are illustrated. <I>Tubiphytes </I>were found to be commonly altered on the ultrastructural scale, inferred to be by dissolution and reprecipitation, but with some preservation of microstructural features such as laminae.

No description available.

Nitrogen-replete cells of <i>Amphidinium carterae</i> took up ammonium in the light at a rate 5 - 6 times that of nitrate even though exponential growth rates were similar on these two N-sources. <i>A. carterae</i> exhibited a capability for enhanced initial ammonium uptake, particularly when deprived of nitrogen. Enhanced initial rates of ammonium uptake were also observed in a natural population of <i>Gyrodinium aureolum</i>. Initially ammonium accumulated within the cells of <i>A. carterae</i> but was assimilated into organic-N within a matter of hours; increases in total cellular-N, total free amino acids, glutamine and cellular protein were observed 4 h after an ammonium addition. In comparison, very little nitrate was accumulated. Ammonium (250 μM) inhibited reversibly the uptake of nitrate; the rapidity of the response suggests a direct effect on uptake. Prior nitrogen deprivation of the cells did not affect this inhibition. Rates of ammonium uptake were similar in the light and dark but nitrate uptake was completely inhibited by darkness in nitrogen replete cells of <i>A. carterae</i> and in a natural population of G. aureolum. Dark uptake of nitrate was stimulated by a period of nitrogen deprivation. Ammonium uptake in darkness by <i>A. carterae</i> was accompanied by the utilization of cellular polysaccharide, mainly glucose polysaccharide. Most of this carbon was unavailable for the assimilation of nitrate in the dark. It is suggested that a control mechanism is in operation, via a product of ammonium assimilation, on one or more of the enzymes concerned with polysaccharide breakdown, e.g. α-amylase or phosphorylase. Ammonium addition caused a marked enhancement of dark CO<SUB>2</SUB> fixation in several nitrogen-replete dinoflagellates. Nitrate addition produced little enhancement in comparison. The amount of enhancement was dependent on species, age of culture and period of diel cycle. Nitrogen deprivation caused a 2-3 fold increase in enhancement in all species tested. The measurement of dark <SUP>14</SUP>CO<SUB>2</SUB> fixation shows promise as a technique for determining the nitrogen status of phytoplankton in both the laboratory and in the field. A natural population of <i>Gyrodinium aureolum</i> appeared to be slightly N-limited using this technique, an observation supported by other field data. The use of this technique as a tool to determine the nitrogen status of phytoplankton in culture and in the field is discussed.

The marine, filamentous, non-heterocystous cyanobacteria, <I>Trichodesmium</I> and <I>Lyngbya</I> sp. UCSB25, are very similar. Both can fix N<SUB>2</SUB> aerobically. However, <I>Trichodesmium</I> differs from <I>Lyngbya</I> sp. UCSB25 and almost all other non-heterocystouc diazotrophs in that it fixes N<SUB>2</SUB> during the day whilst simultaneously photosynthetically evolving O<SUB>2</SUB>. In contrast, <I>Lyngbya</I> sp. UCSB25 and most other non-heterocystous cyanobacteria, perform N<SUB>2</SUB> fixation during the night. During laboratory growth, <I>Trichodesmium</I> sp. IMS 101 effects a temporal separation between maximal rates of N<SUB>2</SUB> fixation and net production of O<SUB>2</SUB>. Thus, peak nitrogenase activity occurs simultaneously with net consumption of O<SUB>2</SUB>. The same is true of <I>Lyngbya </I>sp. UCSB25. Addition of exogenous ammonium (NH<SUB>4</SUB><SUP>+</SUP>), but non nitrate (NO<SUB>3</SUB>), inhibited nitrogenase activity of natural populations and laboratory cultures of <I>Trichodesmium.</I> As in other diazotrops, inhibition caused by NH<SUB>4</SUB><SUP>+</SUP> depends upon its assimilation through the GS-GOGAT pathway. A 30min thermal shock, of 36°C or 40°C to <I>Trichodesmium </I>and <I>Lyngbya</I> sp. UCSB25, respectively, caused a 75% inhibition of nitrogenase activity. In <I>Lyngbya</I> sp. UCSB25 this effect is probably exerted through an inhibition of one or more, kinetically distinguishable O<SUB>2</SUB> uptake system. In <I>Trichodesmium</I> the basis of inhibition was more probably due to a lesion(s) in general metabolism that was independent of O<SUB>2</SUB>. Ascending and descending colonies of natural populations of <I>Trichodesmium</I> show dramatic biochemical differences. Results obtained after the addition of either DCMU or CN suggest that nitrogenase activity in ascending and descending colonies is reliant on respiration and photosynthesis, respectively.

Nitrogenase activity was observed <i>in-situ</i> at two sites dominated by cyanobacteria: Landimore Marsh, Gower, where the diazotroph was on <i>Oscillatoria</i> sp, and Cathole Cave, Gower where the diazotrophic species were <i>Nostoc</i> sp and <i>Gloeothece</i> sp. These sites were surveyed throughout the course of 12 months. The diurnal patterns of nitrogenase activity observed <i>in-situ</i> at each site were found to be characteristic of the cyanobacteria present, and to be identical to the patterns exhibited by laboratory cultures. No activity was observed at either site during the three coldest months of the year, November, December and January. <i>In-situ</i>, and in the laboratory, low temperatures proved to have a greater effect on nitrogenase activity than daylength or light intensity. Nevertheless, in the laboratory lengths of light period below 8-10h out of 24h were found to limit growth by cyanobacterial cultures, N<SUB>2</SUB>-fixing or otherwise. In cultures of <i>Gloeothece</i> or <i>Scytonema</i> maintained under alternating light and darkness N<SUB>2</SUB> fixation in the dark increased markedly as the light intensity during the light period was increased from 5 to 80 uE/m<SUP>2</SUP>/s. In addition, these cyanobacteria proved better able to withstand high light intensities under alternating light and darkness than under continuous illumination. In <i>Gloeothece</i> temperatures of 37<SUP>o</SUP>C or above were found to be inhibitory to both nitrogenase activity and growth. This inhibition was not observed under anaerobic or microaerobic conditions. It therefore appeared that the inhibition was not due to an effect on nitrogenase itself, but rather to an effect on a mechanism for protecting nitrogenase against O<SUB>2</SUB>-inactivation. The patterns of acetylene reduction by cyanobacterial cultures maintained under alternating light and darkness, were unaffected by immobilization in agar cubes, alginate beads, or polyvinyl foam cubes. Furthermore, mixed populations which were unstable in liquid culture, were readily maintained in immobilized cultures.

Procedures to reduce errors in Coulter analyses - In counts of suspensions of algae and inert particles made with a negative external electrode (EE), neither total number of particles per unit volume of suspension nor mean cell or particle volume (MCV) ever changed. In contrast, a count made with a positive EE exhibited a substantial change in MCV. A review of published investigations of damage to red blood corpuscles caused by a count suggests that they are affected in a similar way. Function of the gizzard in Bryozoa - Five gizzard-bearers frequently displayed significantly greater ability to break diatom frustules, when compared with two other bryozoans. The species lacking a gizzard have good ability to separate valves of some diatoms frustules, even to the extent of equalling the percentage broken by the gizzard of <i>Bowerbankia</i>. However, bryozoans that possess a gizzard are small, too small to ingest a majority of the common diatoms. Selection of food by two marine bryozoans - The preferences of <i>Electra pilosa</i> and <i>Flustrellidra hispida</i> have been investigated. <i>E. pilosa</i>, offered mixtures of algae and pollen, did not distinguish between pollen and algal cells but preferentially selected foods of 15-40 um diameter. <i>E. pilosa</i> appears able to select particles with regard to size but not taste, and preferences are affected by total but not relative food concentration. <i>E. pilosa</i> and <i>F. hispida</i> have lophophores of greatly different size, but preferentially selected similar size categories from seston. These were those sizes most abundant in local seawater samples. Optimal design of the bryozoan lophophore - The lateral cilia of <i>Flustrellidra hispida</i> close the intertentacular gap over the proximal 30%, or less, of the length of the gap. A method was developed to study optimal design, and used to determine which characteristics of funnel morphology are optimized by natural selection.

No description available.

The reversible inactivation of nitrate reductase (NR) has been studied in unicellular green algae. The addition of ammonium to nitrate-grown cultures did not result in a rapid loss of NR activity. Losses of NR activity from nitrate-grown cultures that received ammonium were similar to losses that occurred when such cultures were nitrogen starved. Similar results were obtained when either methylamine or arsenate were added to nitrate-grown cultures. Nitrate reductase activity was not inactivated in vitro after preincubation (100 min) with either NAD(P)H or NAD(P)H and ADP, added in equimolar concentrations (0.3mM). The addition of micromolar amounts of cyanide to cell-free extracts from wild-type marine and freshwater algae (11 strains) resulted in a rapid, and almost complete, inactivation of NR activity when NAD(P)H was also included in preincubation mixtures. Cyanide-inactivated enzymes were reactivated after oxidation with ferricyanide. Nitrate had a protective effect against reversible cyanide-inactivation. Nitrate reductase was almost fully active in freshly prepared extracts from nitrate-grown cultures of most species. Nitrate reductase activity in freshly prepared extracts from nitrate-grown cultures of Chlorella vulgaris and Chlorella variegata, were activated substantially after preincubation with terricyanide. Nitrate reductase from the nit A mutant of Chlamydomonas reinhardii 17/4 was not inactivated after preincubation with NAD(P)H and cyanide; reversible cyanide-inactivation of the mutant enzyme did occur in extracts preincubated with cyanide and, either reduced flavin mono-nucleotide or reduced benzyl viologen. The cyanide inactivated, mutant enzyme was reactivated by ferricyanide. The pyridine nucleotide specificity of NR from eleven algal strains was investigated. Only five strains contained NADH-NR and NADPH-NR activities; none contained NADPH-NR activity only. Further studies of the pyridine nucleotide specificity of algal NR were carried out by (i) using pyridine nucleotide analogues (ii) investigating the effectiveness of NADH and NADPH as protectants against p-chloromercuribenzoate (p-CMB) inactivation and (iii) comparing NADH and NADPH as effectors in reversible cyanide inactivation. The bispecific, NAD(P)H-NR of Chlorella variegata was purified by Blue Sepharose (CL-6B) affinity chromatography. Apparent Km values for NAD(P)H and nitrate were obtained and other properties of the enzyme were studied.

The expression of NADPH-specific glutamate dehydrogenase (NADPH-GDH) was examined in <i>Euglena gracilis</i> Klebs strain z Pringsheim in relation to light and available nitrogen source. The exposure of dark-grown resting cells to white or red light caused a transient increase in NADPH-GDH specific activity over the first 12 hours of regreening. Nitrogen-starved or cells grown on glutamate had high NADPH-GDH activity but activity was completely repressed in cells grown on ammonium bicarbonate as sole nitrogen source. These characteristics of the dehydrogenase suggest that the enzyme has a catabolic function in <i>Euglena</i> generating NH<SUP>+<SUB>4</SUB></SUP> from glutamate under conditions of nitrogen limitation. NADPH-GDH was purified from glutamate-grown cells. The homogenously pure protein was characterised (subunit relative molecular mass, 45,000 daltons) and used for antibody production in rabbit. Monospecific anti-(NADPH-GDH) serum obtained was used to detect nascent NADPH-GDH in rabbit reticulocyte lysates programmed with <i>Euglena</i> poly(A)<SUP>+</SUP>RNA in order to determine the relative abundance of NADPH-GDH poly(A)<SUP>+</SUP>RNA in relation to enzyme expression. By immunochemical titration using the specific antiserum the increase in NADPH-GDH activity in glutamate-grown and regreening cells was shown to be the result of an increase in enzyme protein. Poly(A)<SUP>+</SUP>RNA extracted from cells grown on different nitrogen sources and regreening cultures was used to programme reticulocyte lysates. The immunoprecipitation of nascent NADPH-GDH from lysates showed that changes in enzyme levels in response to substrate provision or during regreening were not reflected in levels of its poly(A)<SUP>+</SUP>RNA. The results suggest that the synthesis of NADPH-GDH is regulated primarily at the post-transcriptional level in <i>Euglena</i>. NADPH-GDH poly(A)<SUP>+</SUP>RNA could not be detected on polysomes of dark-grown resting cells although the abundance of poly(A)<SUP>+</SUP>RNA encoding NADPH-GDH was apparently unaltered in these cells. NADPH-GDH was detected on polysomes from dark-grown resting cells after 6 and 12 hours of illumination. This implies that light elicits a mobilisation of a pre-existing NADPH-GDH poly(A)<SUP>+</SUP>RNA onto polysomes of regreening cultures promoting enzyme synthesis.