Response of lake phytoplankton communities to in situ manipulations of light intensity and colour

Phytoplankton preferences for light intensity and colour weredetermined in field experiments using coloured plexiglass cubessuspended at different depths in Heney Lake, Québec.Diatoms and green algae favoured intensities greater than 1%I_o (surface irradiance) contrary to dinoflagellates and otherflagellates that preferred lower intensity. Red radiation usuallyincreased the relative proportion of blue-greens, diatoms andgreen algae, whereas it reduced that of dinoflageilates. Wepropose that differential utilization of the light gradientallows certain phytoplankton taxa to partition the water column,thereby reducing potential competition. This is supported bythe general agreement between our findings and the known depthdistribution of algae in lakes.     

The isolation and partial characterization of the plasma membrane from Trypanosoma brucei.

Whole sheets of plasma membrane, each with their attached flagellum, were purified from Trypanosoma brucei. The method devised for their isolation included a new technique of cell breakage that used a combination of osmotic stress followed by mechanical sheer and avoided the problem of extreme vesiculation as well as the trapping of organelles in cell 'ghosts'. The purified membranes all contained the pellicular microtubular array. The antigenic surface coat was completely released from the plasma membrane during the isolation procedure. The membranes had a very high cholesterol/phospholipid ratio (1.54). A large proportion (42%) of the cellular DNA was recovered in the plasma-membrane fraction unless a step involving deoxyribonuclease treatment, which decreased the DNA content to less than 13%, was included before secrose-density gradient centrifugation. This step also aided the separation of plasma membranes from other cellular components. The ouabain-sensitive Na+ + K+-stimulated adenosine triphosphatase and adenylate cyclase co-purified with the plasma membranes. Although 5'-nucleotidase was thought to be a plasma-membrane component, it was easily detached from the membrane. The purified membranes were essentially free of L-alanine-alpha-oxoglutarate aminotransferase, L-asparte-alpha-oxoglutarate aminotransferase, malate dehydrogenase, oligomycin-sensitive adenosine triphosphatase, glucose 6-phosphatase, Mg2+-stimulated p-nitrophenyl phosphatase and catalase.     

Quantitative aspects of RNA synthesis in normal and lithium-treated embryos ofXenopus laevis

Summary The treatment ofXenopus early embryos with lithium chloride produces exogastruale — embryos which fail to gastrulate normally and in which the rates of cell division are reduced. In the present study estimations of incorporations of (5-³H) uridine and the specific activities of the 5-ribonucleotide precursor pools showed that exogastrulae have higher rates of RNA synthesis per cell than control neurulae. Sub-cellular fractionations showed that a greater proportion of labelled RNA was retained in the nuclei of exogastrulae than of neurulae, while neurulae showed a greater incorporation into polysomes.     

The creation and management of wildfowl refuges as a means of lessening the conflict between farmers and geese

With increases in goose numbers and incidences of problems with other than traditionally damaging species on new crops conflict has greatly increased recently. This paper suggested that the creation of managed goose refuges in problem areas provided the best long-term solution. Examples of the success of refuges were given based on experience at two Wildfowl Trust goose refuges. Goose use of land surrounding these refuges had decreased following their creation and the goose carrying capacity of refuge land had been increased by up to 150% by controlling winter disturbance, cropping and stock grazing. This had been achieved without drastically changing the agricultural regime, which in both areas was in line with local practices. Because of great annual fluctuations in goose numbers following variations in breeding success and of the difficulty of predicting goose carrying capacity, assessments of the area of land required to accommodate geese in conflict with agriculture in Britain can only be very approximate. Based on goose counts in 1975-6, some 150000 geese (of four species) were potentially involved and the land area required as refuges to accommodate all of them (giving a maximum figure) in the region of 20 000 acres (7800 ha).     

Effect of methylmalonate on ketone body metabolism in developing rat brain

The oxidation of 3-hydroxy[3-¹⁴C]butyrate to CO₂ and its incorporation into cerebral lipids by cortex slices from one-week old rats were markedly inhibited by methylmalonate. However, methylmalonate had no effect on the metabolism of labelled aceto- acetate, glucose and acetate by brain slices. Addition of propionate in the incubation medium reduced cerebral lipogenesis from labelled 3-hydroxybutyrate and acetate. Acute methylmalonic acidemia induced in one-week old pups by injecting 3% methylmalonate solution caused a reduction in the incorporation of labelled 3-hydroxybutyrate into cerebral lipids. However, acute methylmalonic acidemia had no effect on cerebral lipogensis $\text{in vivo}$ from labelled acetate. These findings show (i) the conversion of 3-hydroxybutyrate to acetoacetate by 3-hydroxybutyrate dehydrogenase in the brain is inhibited by methylmalonate, and (ii) an inhibition of cerebral lipid synthesis by propionate, which also accumulates in patients with methylmalonic aciduria.     

Deoxyribonucleic acid reassociation in the classification of flavobacteria.

DNA-DNA reassociation studies showed that Flavobacterium emningosepticum strains had a genetic relatedness of 91 to 100% with inter-strain duplexes having high thermal stabilities. The only exception, strain NCTC10016, had an average relatedness of only 43% to other strains of F. meningosepticum. The apparent divergence in DNA base sequence of this strain was reflected in the structural differences of some enzymes. There was a gradation of DNA relatedness among the Flavobacterium group II-b strains, but three strains were sufficiently related to constitute a species. Low levels of genetic relatedness were confirmed between F. meningosepticum and strains of Flavobacterium group II-b, group II-f, F. aquatile, F. breve, F. heparinum, F. pectinovorum, F. odoratum and Moraxella saccharolytica. All strains had base compositions in the range 32 to 46% guanine plus cytosine. The genome sizes of representative strains of F. meningosepticum and Flavobacterium group II-b were 2-50 X 10(9) to 3-52 X 10(9) daltons. The taxonomic implications of these findings are discussed.     

The invisible copper of cytochrome c oxidase. pH and ATP dependence of its midpoint potential and its role in the oxygen reaction.

Formation of the CO compound has been studied in intact mitochondria, submitochondrial particles and isolated cytochrome oxidase. The reaction requires the prior reduction of both cytochrome a₃ and one other single-electron acceptor. It is inferred that the second acceptor is the “invisible” copper which is undetectable by both optical and spin resonance spectroscopy. The overall process can be viewed as two single electron steps plus a ligand binding reaction. At high concentrations of CO, when titrations are performed at oxidation-reduction potentials significantly above the midpoints of either cytochrome a₃ or “invisible” copper, appearance of the CO compound follows a strict n = 2 (2-electron) relationship. Its midpoint potential is also dependent on the prevailing concentration of CO and is increased by approx. 30 mV for each tenfold increase in the level of CO. At redox potentials approaching the midpoints of cytochrome a₃ or “invisible” copper, significant deviations from n = 2 behavior are apparent which are readily detectable experimentally using low CO concentrations.A mathematical analysis of this model is presented and the oxidation-reduction properties of the CO compound are utilized to determine the midpoint potential of the “invisible” copper. This value is estimated to be 340 ± 10 mV at pH 7.8, independent of pH and the prevailing $\text{sol}\text{[ATP]}\text{[ADP]}\text{× [}\text{P}{}_1\text{]}$ ratio.By analogy with the observations on CO binding, the primary intermediate in the oxidase reaction with oxygen is concluded to be a bridged a₃²⁺-O₂-Cu¹⁺ complex. The initial reduction of molecular oxygen can then proceed via a thermodynamically favorable two-electron step to form a bridged peroxide intermediate. Subsequent reduction to water may later occur by way of two single-electron steps or one two-electron step.