Distribution and composition of particulate organic matter in the Ross Sea (Antarctica)

The biochemical composition and spatial distribution of particulate organic matter (POM) were studied in the Ross Sea (Antarctica) in summer 1989 to assess the quantitative role of organic carbon fractions in the cycling of organic matter in the water column. Large differences in chemical composition were observed between surface and deep layers. The results indicated that, despite large geographical differences, POM was quite homogeneous, of phytoplankton origin and mostly detrital. Different ratios were used to investigate the changes in biochemical composition of particulate organic matter in relation to the ice-melting: CN (organic carbonorganic nitrogen ratio) and C-POMPOC (sum of carbohydrate, protein and lipid carbontotal organic carbon ratio) were used to analyse the percentage of refractory organic material. PPRTPCHO (proteincarbohydrate ratio) were used to establish POM age and RNADNA ratios as a relative measure of particulate activity; POCChl a and N-PPRTChl a ratios were used to estimate the autotrophic contribution to the suspended particulate organic matter. Despite its low caloric value (5.3 Kcal g POM^–1), an high caloric content in the photic layer (1.6 Kcal m^–3 of POM and 2.5 Kcal m^–3 of POC) was found thus indicating that a large amount of food was available to higher trophic levels.     

Freshwater protozoa: biodiversity and ecological function

The purpose of this article is to pull together various elements from current knowledge regarding the natural history of free-living protozoa in fresh waters. We define their functional role, set the likely limits of biodiversity, and explore how the two may be related. Protozoa are unicellular, phagotrophic organisms, and 16 phyla of protists contain free-living freshwater protozoan species. They are the most important grazers of microbes in aquatic environments and the only grazers of any importance in anoxic habitats. In sediments, ciliates are usually the dominant protozoans. Benthic ciliate biomass accounts for slightly less than 10% of total benthic invertebrate biomass, but ciliate production may equal or even exceed invertebrate production. Freshwater protozoan species are probably ubiquitous, although many may persist locally for long periods in a cryptic state – as potential rather than active biodiversity. As protozoa are among the largest and most complex of micro-organisms, it follows that bacteria and all other smaller, more numerous microbes are also ubiquitous. The number of protozoan species recorded in local surveys (232) is about 10% of the estimated global species richness (2390). The 'seedbank of protozoan (and microbial) species ensures that local microbial diversity is never so impoverished that it cannot play its full part in ecosystem functions such as carbon fixation and nutrient cycling.     

Sources of organic carbon in mangrove sediments: variability and possible ecological implications

Mangrove sediments from three different mangrove ecosystems (Coringa Wildlife Sanctuary in the Godavari Delta, Andhra Pradesh, India, and Galle and Pambala, south-west Sri Lanka) were analysed for their organic carbon content, elemental ratios (C:N) and carbon stable isotope composition. Organic carbon content (0.6 – 31.7% dry weight), C/N ratios (7.0 – 27.3) and ¹³C (between –29.4 and –20.6) showed a wide range of values. Lower stocks of organic carbon coincided with low C/N (atom) ratios and less negative ¹³C values, indicating import of marine or estuarine particulate suspended matter. High organic carbon stocks coincided with high C/N ratios and ¹³C values close, but not equal, to those of the mangrove vegetation. The variations observed in this study and published literature data could be adequately described by a simple two-end mixing model, whereby marine/estuarine suspended matter and mangrove litter were taken as end members. Thus, while in some mangrove ecosystems or vegetation zones, organic carbon stocks can be very high and are almost entirely of mangrove origin, there also appear to be cases in which deposited estuarine or marine suspended matter is the dominant source of organic carbon and nitrogen in mangrove sediments. This situation is remarkably similar to that observed in temperate salt marsh ecosystems where the importance of local vascular plant production to the sediment organic carbon pool is equally variable. The observed high variability in organic matter origin is thought to have a major impact on the overall carbon dynamics in intertidal mangrove ecosystems.     

Development and ecological importance of phytoplankton in a large lowland river (River Meuse,Belgium)

The ecological importance of the River Meuse phytoplankton with regard to carbon and nutrient transport has been examined in two reaches of the Belgian course of the river.Field measurements of total particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate phosphorus (PP) show that the large autochtonous production of organic matter strongly affects the carbon and nutrient budget of the aquatic system. During the growing season, phytoplankton accounts for nearly 60% of the POC and dominates the PON. Calculations of the carbon and oxygen budget in the upper reach of the Belgian Meuse demonstrates that the ecosystem is autotrophic, i.e. that autochtonous FPOM (fine particulate organic matter) production is the major carbon input. This suggests that in large lowland rivers, primary production (P) may exceed community respiration (R), i.e. P:R>1, whereas they are assumed to be heterotrophic (P:R<1) in the River Continuum concept.The question of maintenance of phytoplankton in turbid mixed water columns is also addressed, and the case of the River Meuse is treated on the basis of studies of photosynthesis and respiration (ETS measurements). The results suggest that the potamoplankton may show some low-light acclimation, through an increase of chlorophyll a relative to biomass, when it comes to deep downstream reaches, and that algal respiration rate may be reduced. A simulation of the longitudinal development of the algal biomass shows the different phases of algal growth and decline along the river and brings support to the importation hypothesis for explaining maintenance of potamoplankton in the downstream reaches.     

Gender- and age-specific contributions of additional DNA sequence variation in the 5′ regulatory region of the <Emphasis Type="Italic">APOE</Emphasis> gene to prediction of measures of lipid metabolism

In the present study of 9,000 individuals representative of the general population, we have considered whether the addition of common single nucleotide polymorphisms (SNPs) in the promoter region of Apolipoprotein E (APOE) improve the statistical explanation of variation in lipid traits and test the hypothesis that the estimated genotype effects are independent of factors indexed by gender and age. To address these questions, we have asked, for each gender and for each 20-year age strata (young: 20–39 years; middle-aged: 40–59 years; old: 60–79 years; very old: 80–100 years), how much trait variation is associated with the traditional 2, 3, and 4 allelic variations defined by the g.2059TC and g.2197CT SNPs in the fourth exon of the APOE gene, and how much additional trait variation is associated with genotypes defined by combining the g.2059TC and g.2197CT SNPs with one, two, or three promoter SNPs. Our study demonstrates that the pleiotropic effects of genotype variation defined by the traditional 2, 3, and 4 alleles on five plasma measures of lipid metabolism manifest differently in women and men and change significantly during the life cycle for high-density lipoprotein cholesterol in women. Multi-site genotypes defined by adding SNPs located in the 5 promoter region to the traditional g.2059TC and g.2197CT SNPs doubled the estimate of genetic variance of high-density lipoprotein and apolipoprotein Al in middle-aged females.     

The fiber composition of the semitendinosus muscle of the rabbit

Summary The semitendinosus muscle of the rabbit is composed of a homogeneous fiber population. Fiber typing was carried out by means of light and electron microscopy according to which this muscle exhibits structural features that are either characteristic for both red and white fibers, or that do not allow for any classification according to the A-, B-, C-fiber system. Hence the long-held assumption that the semitendinosus muscle of the rabbit represents a classical paradigm of a red muscle should be revised in light of the present results.     

Biosynthesis,cDNA and amino acid sequences of a precursor of conglutin δ, a sulphur-rich protein from Lupinus angustifolius

The biosynthesis of conglutin has been studied in developing cotyledons of Lupinus angustifolius L. Precursors of conglutin formed the major sink for [³⁵S]-cysteine incorporated by developing lupin cotyledons, and these precursors were rapidly sequestered into the endoplasmic reticulum. The sequence of a cDNA clone coding for one such precursor of conglutin was determined. The structure of the precursor polypeptide for conglutin predicted from the cDNA sequence contained an N-terminal leader peptide of 22 amino acids directly preceding a subunit polypeptide of M _r 4520, together with a linking region of 13 amino acids and a subunit polypeptide of M _r 9558 at the C-terminus. The amino acid sequence predicted from the cDNA sequence showed minor variations from that established by sequencing of the protein purified from mature dried seeds (Lilley and Inglis, 1986). These were consistent with the existence of a multi-gene family coding for conglutin . Comparison of the sequences of conglutin with those of other 2S storage proteins showed that the cysteines involved in internal disulphide bridges between the mature subunits of conglutin , were maintained throughout this family of proteins but that little else was conserved either at the protein or DNA level.     

Variant MoFe proteins of Azotobacter vinelandii: effects of carbon monoxide on electron paramagnetic resonance spectra generated during enzyme turnover

The resting state of wild-type nitrogenase MoFe protein exhibits an S=3/2 electron paramagnetic resonance (EPR) signal originating from the FeMo cofactor, the enzymes active site. When nitrogenase turns over under CO, this signal disappears and one (sometimes two) of three new EPR signals, which also arise from the FeMo cofactor, appears, depending on the CO concentration. The appearance and properties of these CO-inducible EPR signals, which were also generated with variant MoFe proteins (R96Q, R96K, Q191K, R359K, R96K/R359K, R277C, R277H, and nifV) that are impacted around the FeMo cofactor, have been investigated. No new CO-induced EPR signals arise from any variant, suggesting that no new CO-binding sites are produced by the substitutions. All variant proteins, except R277H, produce the lo-CO signal; all, except Q191K, produce the hi(5)-CO signal; but only two (R96Q and nifV) exhibit the hi-CO signal. FeMo cofactors environment clearly dictates which CO-induced EPR signals are generated; however, none of these EPR signals correlate with CO inhibition of H₂ evolution observed with some of these variants. CO inhibition of H₂ evolution is, therefore, due to CO binding to a different site(s) from those responsible for the CO-induced EPR signals. Some resting-state variants have overlapping S=3/2 EPR signals, whose intensities simultaneously decrease under turnover conditions, indicating that all FeMo cofactor conformations are catalytically active. Moreover, these variants produce a similar number of hi(5)-CO signals after turnover under CO to the number of resting-state S=3/2 signals. The FeMo cofactor associated with the hi(5)-CO signal likely contains two bridging CO molecules.     

Landscape ecology as a bridge from ecosystems to human ecology

Landscape as a subject of (terrestrial) ecology can be interpreted: first, as a piece of land composed of different ecosystems; and second, as a holistic entity of aesthetic perception derived from landscape paintings and parks of the 18th and 19th century. Such entities display a characteristic arrangement of landscape elements regarded as a whole and taking them apart for specific investigation will break up and virtually destroy it (e.g. a symphony dissociated into single notes). Landscape as a holistic entity satisfies emotional human needs like identification with regions, and explains the attraction of tourists. Entity features are land-use and land cover combined with openness and a certain naturalness. A key question is whether you call a piece of the earths surface just land or landscape– and why. Such questions touch the interface between landscape ecology and human ecology. But human ecology must not dismiss landscape functions. The most beautiful landscape will be reduced to a mere picture if it does not also provide basic life-support. Therefore, energy and matter flows and transformations between the ecosystems of a landscape have to be determined along with its climate, geomorphology (relief), soils, hydrology, species and ecosystem diversity. These different approaches, however, may never be combined into a unified whole. There is no superscience, and incidentally, its complexity would by far exceed human brain capacity. What we can achieve is bridge-building by approximation of selected facts. A conscious spatial arrangement of diversified land-use units (ecotopes) will promote (bio)diversity and may be perceived as an integral landscape pattern. A spatially and temporally differentiated energy input into land-use units will result in a gradient of utilization intensity and allow more species to thrive, again enhancing both diversity and landscape beauty. Modern humans have deliberately chosen artificial surroundings to achieve complete environmental control, even in rural lifestyles. But as far as emotional needs are concerned, this artificiality seems to be neither human nor ecological. Something natural is lacking, and landscape in its holistic sense can provide it – be it a landscaped open space in a city, a rural scene, a seashore or a mountain range. Maintaining and managing such naturalness requires sound ecological knowledge – not as an aim in itself, but to provide a bridge for humans.     

DDT concentrations in surficial sediments of three estuarine systems in Portugal

Levels of p,p-DDT and its metabolites in surficial sediments of Tagus and Sado Estuary and lagoon Ria Formosa varied one or two orders of magnitude. In general, p,-DDE and p,-DDD were the dominant metabolites and p,-DDT was a minor component. While concentrations of p,-DDT, p,-DDD and p,-DDE were hardly related to loss on ignition, concentrations of total DDT (tDDT) in surficial sediments of each studied system were positively correlated to that parameter. Higher contaminated samples were excluded from these relationships: a few sediment samples from the Tagus outlet channel, most of the sediments from the upper Sado Estuary, and some particulate matter samples collected in sediment traps in the adjoining area to the Ria Formosa. Concentration of tDDT appears, thus, to be related to sedimentary organic matter of these estuarine systems except near the actual sources of pollution. On the basis of the relationship slopes, one may conclude that lower Tagus Estuary is more contaminated than Ria Formosa and lower Sado Estuary.     

Autotrophic carbon sources for heterotrophic bacterioplankton in a floodplain lake of central Amazon

The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (¹³C) were used as tracers. Values of ¹³C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO₂.The percentage of carbon derived from C₄ macrophytes for bacterially produced CO₂ was the highest, on average 89%. The average ¹³C value of CO₂ from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO₂ of 3 by bacterial respiration, ¹³C value was –15.5, near C₄ macrophyte ¹³C value (–13.1).The average value of total DOC ¹³C was –26.8 ± 2.4. The percentage of C₄ macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C₃ plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C₄ macrophytes to the consumers.     

The pancreatic islets of the teleost Scorpaena scropha

Summary The principal pancreatic islets of the teleost Scorpaena scropha are found ultrastructurally to contain four different kinds of parenchymal cells, viz. ₁-(= D), ₂-, -and agranular cells. The -cells show considerable variations in the shape of the secretory granules. A peculiar feature is that many of these granules are composed of fibrillar subunits, often in parallel arrangement. All -granules are surrounded by membranes and between the membrane and the granule core there is a moderately wide electron lucent space. The electron density of the cytoplasm in the -cells varies somewhat. The ₂-cells possess typical secretory granules with an electron dense core and a closely applied membrane. The secretory granules in the ₁-cells show also a closely applied membrane but a less dense core. Also in the -cells the electron opacity of the cytoplasm varies. The agranular cells are mainly characterized by low cytoplasmic electron density, narrow cisterns of endoplasmic reticulum and sometimes a laminated Golgi complex. Small immature secretory granules are occasionally seen in the cytoplasm of these cells. The significance of the fibrillar -granules remains obscure.This work was supported by grants from the Nordic Insulin Fund, the Town of Umeå, the Swedish Medical Research Council (Project No. B69-12X-718-04A), and by a postdoctoral fellowship from the United States Public Health Service.     

Seasonal and diel relationships between the isotopic compositions of dissolved and particulate organic matter in freshwater ecosystems

A study of the isotopic composition of organic matter was conducted in a freshwater marsh over seasonal and diel time scales to determine the sources of dissolved organic matter (DOM) and the processes leading to its formation. Bulk C and N isotopic compositions of the bacterial fraction (0.2–0.7 m) and particulate organic matter (POM; 0.7–10 m) were compared on a seasonal basis with the change in ¹³C of DOM. The bulk isotopic data support the idea that DOM was, in part, derived from the breakdown of larger organic matter fractions. The bacterial fraction and POM were compositionally similar throughout the year, based on a comparison of the ¹³C of individual amino acids in each fraction. Annual variation in the ¹³C of amino acids in DOM was greater relative to the variation in larger fractions indicating that microbial reworking was an important factor determining the proteinaceous component of DOM. The ¹³C enrichment of serine and leucine in each organic matter fraction suggested microbial reworking was an important factor determining organic matter composition during the most productive times of year. Changes in the bulk ¹³C of DOM were more significant over daily, relative to seasonal, time scales where values ranged by 6 and followed changes in chlorophyll a concentrations. Although bulk ¹³C values for POM ranged only from –29 to –28 during the same diel period, the ¹³C of alanine in POM ranged from –30 to –22. Alanine is directly synthesized from pyruvate and is therefore a good metabolic indicator. The ¹³C of individual amino acids in DOM revealed the diel change in the importance of autotrophic versus heterotrophic activity in influencing DOM composition. Diel changes in the ¹³C of phenylalanine, synthesized by common pathways in phytoplankton and bacteria, were similar in both DOM and POM. The diel change in ¹³C of isoleucine and valine, synthesized through different pathways in phytoplankton and bacteria, were distinctly different in DOM versus POM. This disparity indicated a decoupling of the POM and DOM pools, which suggests a greater source of bacterial-derived organic matter at night. The results of this study demonstrate the use of the isotopic composition of individual amino acids in determining the importance of microbial reworking and autotrophic versus heterotrophic contributions to DOM over both diel and seasonal time scales.     

On the appropriateness of use of a continuous formulation for the modelling of discrete multireactant systems following Michaëlis–Menten kinetics

The possibility of solving the mass balances to a multiplicity of substrates within a CSTR in the presence of a chemical reaction following Michaelis-Menten kinetics using the assumption that the discrete distribution of said substrates is well approximated by an equivalent continuous distribution on the molecular weight is explored. The applicability of such reasoning is tested with a convenient numerical example. In addition to providing the limiting behavior of the discrete formulation as the number of homologous substrates increases, the continuous formulation yields in general simpler functional forms for the final distribution of substrates than the discrete counterpart due to the recursive nature of the solution in the latter case.List of Symbols C{N. M} mol/m³ concentration of substrate containing N monomer residues each with molecular weight M - {N, M} normalized value of C{N. M} - C {M} mol/m³ da concentration of substrate of molecular weight M - _in normalized value of C {M} at the i-th iteration of a finite difference method - {M} normalized value of C {M} - C ₀{N.M} mol/m³ inlet concentration of substrate containing N monomer residues each with molecular weight M - {N ·M} normalized value of C₀{N. M} - _{0 i} normalized value of C ₀ {M} at the i-th iteration of a finite difference method - C ₀ {M} mol/m³ da initial concentration of substrate of molecular weight M - C _tot mol/m³ (constant) overall concentration of substrates (discrete model) - C _tot mol/m³ (constant) overall concentration of substrates (continuous model) - D deviation of the continuous approach relative to the discrete approach - i dummy integer variable - I arbitrary integration constant - j dummy integer variable - k dummy integer variable - K _m mol/m³ Michaëlis-Menten constant for the substrates - l dummy integer variable - M da molecular weight of substrate - M normalized value of M - M da maximum molecular weight of a reacting substrate - N number of monomer residues of a reacting substrate - N maximum number of monomer residues of a reacting substrate - N total number of increments for the finite difference method - Q m³/s volumetric flow rate of liquid through the reactor - S inert product molecule - S _i substrate containing i monomer residues - V m³ volume of the reactor - v _max mol/m³ s reaction rate under saturating conditions of the enzyme active site with substrate - v _max{N. M} mol/m³ s reaction rate under saturating conditions of the enzyme active site with substrate containing N monomer residues with molecular weight M - _max{N · M} dimensionless value of v_max{N. M} (discrete model) - _max{M} dimensionless value of v _max {M} (continuous model) - mol/m³ s molecular weight-averaged value of v_max (discrete model) - mol.da/m³s molecular weight-averaged value of v_max (continuous model) - v _max {M} mol.da/m³s reaction rate under saturating conditions of the enzyme active site with substrate with molecular weight M - _max {M} dimensionless value of v_max{M} - _{max, (i)} dimensionless value of v_max{M} at the i-th iteration of a finite difference method - v _max mol/m³ s reference constant value of v _max Greek Symbols dimensionless operating parameter (discrete distribution) - dimensionless operating parameter (continuous distribution) - M da (average) molecular weight of a monomeric subunit - M selected increment for the finite difference method - auxiliary corrective factor (discrete model)     

Geochemical composition of sediments in the Scheldt estuary with emphasis on trace metals

Superficial sediments of the Scheldt estuary were collected with a Van Veen grab at 57 stations between Temse and Vlissingen. They were analysed for major elements (Si, Al, Fe, Ca, Mg, Na, K, Cinorg and Corg) and trace metals (Cd, Pb, Cu, Zn, Cr, Ni, Co, Mn and Li). Factor analysis indicates that 44% of the variance can be explained by one factor which exhibits a high saturation for trace metals, organic matter, Al and Fe, all variables typical of fine mud. The high scores of this first factor are almost exclusively present in the upper estuary except for one area in front of Terneuzen. The second factor, which explains 23% of the variance, is typical of the carbonates and the third one (19% of the variance) is representative of the clay minerals. These two factors are more evenly distributed over the estuary. As usual, a strong influence of granulometry on the distribution of trace elements in the sediments was observed. Intercomparison of their composition within the Scheldt or with those of other aquatic systems requires thus a normalization procedure. This problem has been studied in detail by analysing various size fractions (63–16, 16–8, 8–4, <4 m) obtained by elutriation of the sample or by using a parameter characteristic of the fine fraction such as the concentration of a typical element (Al, Fe, Li, Corg). The normalization of trace metals allowed us to evaluate an enrichment factor of the trace elements in the estuarine deposits due to mans activities. In addition, it demonstrates the decrease of the anthropogenic impact on the composition of sediments by comparing the composition of sediments collected in 1976 and in 1994.     

Microbial transformation of α-pinene

Summary A bacterium capable of utilizing -pinene as a sole carbon and energy source was isolated from soil. This strain, named strain S201-1, which was identified as Pseudomonas maltophilia on the basis of its taxonomical properties, accumulated limonene, borneol, camphor, perillic acid, and 2-(4-methyl-3-cyclohexenylidene) propionic acid from -pinene in the culture broth. It was demonstrated that -pinene, -pinene, borneol, camphor, and a number of p-menthane derivatives were oxidized by this strain. Relations between the protonation of -pinene and the formation of the products by the microbe are discussed.     

Sodium efflux from perfused giant algal cells

Internodal cells of the giant alga Chara corallina were perfused internally to replace the native cytoplasm, tonoplast and vacuole with artificial cytoplasm. Sodium efflux from perfused cells, measured by including ²²Na in the perfusion media, was increased by increasing the internal sodium concentration and by decreasing the external pH, and was inhibited by external application of the renal diuretic amiloride. The sodium efflux was markedly ATP-dependent, with a 50-fold decrease in efflux observed after perfusion with media lacking ATP. Efflux in the presence of ATP was reduced by 33% by inclusion of 10 M N,N-dicyclohexylcarbodiimide in the perfusion medium. The membrane potential of the perfused cells approximated that of intact cells from the same culture. It is suggested that sodium efflux in perfused Chara cells proceeds via a secondary antiporter with protons, regulated by ATP in a catalytic role and with the proton motive force acting as the energy source.Abbreviations DCCD N,N-dicyclohexylcarbodiimide - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - Mes 2-(N-morpholino)ethanesulphonic acid - Mops 3(N-morpholino)propanesulphonic acid - Taps tris(hydroxymethyl)methylaminopropanesulphonic acid     

Sources and fluxes of particulate organic matter in shallow coastal waters characterized by summer macroaggregate formation

The origin and temporal variation in composition of sedimented particulate organic matter (POM) in the Gulf of Trieste (northern Adriatic) was studied over the year with special reference to the composition and sedimentation of macroaggregates in summer of 1991 using sediment traps.Suspended and sedimented POM, comprising a minor part of the largely inorganic total particulate matter, was prevalently of marine origin and composed mostly of humic substances followed by carbohydrates and proteins. Seasonal variations of particulate proteins and carbohydrates were correlated with variations of phytoplankton biomass. New production, occurring in late spring as a consequence of massive riverine inputs of N, Si and P nutrients in the surface layer of the Gulf, produced high particulate carbohydrate and protein concentrations. Subsequent depletion of introduced nutrients caused the decrease of particulate protein concentration but not that of particulate carbohydrate. The prolonged plankton biosynthesis of carbohydrates successively produced marine snow and later macroaggregates. The macroaggregates were characterized by ¹³C value of –19.9. and their carbohydrates were mostly composed of glucose followed in decreasing order by mannose, fructose, galactose, arabinose, ribose, xylose and fucose, suggesting a prevalent origin from phytoplankton structural heteropolysaccharides. Sedimentation of particulate organic constituents in the summertime, characterized by the massive presence of macroaggregates in the surface layer above the pycnocline, was the highest at a depth of 10 m at the end of this phenomenon, about six weeks after its first appearance. Sedimented macroaggregates were clearly traced by a characteristic ¹³C signal and higher carbohydrate concentrations. The monosaccharide composition was influenced by selective degradation in the water column. Sedimented POM in the bottom layer was, on the other hand, more affected by sediment resuspension. The mean yearly decrease of particulate protein-C and carbohydrate-C by 40–50% in the water column between the depths of 10 and 20 m indicates the preferential utilization of these constituents by microorganisms. The decrease of particulate humic-C is probably more the result of the export of particulate matter from the Gulf. This study also indicates that the macroaggregate formation has little impact on the annual C and N budget in such coastal areas.     

A 43 kD light-regulated chloroplast RNA-binding protein interacts with the psbA 5′ non-translated leader RNA

Expression of the chloroplast psbA gene coding for the D1 protein of Photosystem II is subject to regulation at different levels in higher plants, including control of mRNA accumulation and translation. In dicots, the conserved 5 non-translated leader (5-UTR) of the psbA mRNA is sufficient to direct the light-dependent translation of the D1 protein. In this report we show that the psbA mRNA 5-UTR forms a stem-loop structure and binds a 43 kD chloroplast protein (43RNP). Binding of the 43RNP is sensitive to competition with poly(U), but insensitive to high concentrations of tRNA, the RNA homopolymers poly(A), poly(G), poly(C), or poly(A):poly(U) as a double-strand RNA. The 43RNP does not bind efficiently to the psbA mRNA 3 non-translated region, although the RNA sequence is U-rich and folds into a stem-loop. A deletion mutant of the psbA 5-UTR RNA in which 5 sequences of the stem-loop are removed does not affect 43RNP binding. Together, these properties suggest that the 43RNP binds most effectively to a specific single-strand U-rich sequence preceding the AUG start codon in the psbA mRNA. Binding of the 43RNP is not detectable in plastid protein extracts from 5-day-old dark-grown seedlings, but is detectable in light-grown seedlings as well as mature plants in the light and after shifted to the dark. The 43RNP is therefore a candidate for a regulatory RNA-binding protein that may control the accumulation and/or translation of the psbA mRNA during light-dependent seedling development.Abbreviations DMS dimethylsulfate - psb Photosystem II genes - RNP ribonucleoprotein - UTR non-translated leader - UV crosslinking ultra-violet light crosslinking     

Pi Mheerlen,a Pi M allele resulting in very low a 1-antitrypsin serum levels

Summary A patient with pulmonary emphysema is described, who had a very low ₁-antitrypsin serum concentration (2% of normal). After isoelectric focusing and staining, the patient's serum revealed no visible ₁-antitrypsin bands. Immunofixation, following isoelectric focusing, gave a banding pattern identical to that of a normal M type. The existence of this deficient M-allele was confirmed by family studies. Low ₁-antitrypsin concentrations, due to the presence of the deficient allele, were coupled with low serum antitrypsin activities.