Bacterial secondary production and it relation with primary production in the Embalse del Río III Reservoir,Argentina

During an annual period the bacterial biomass (epifluorescence) and secondary production (methyl-³H-thymidine incorporation), as well as biomass (Chlorophyll) and algal primary production (incorporation of NaH¹⁴CO₃) were studied in the Embalse del Río III Reservoir, Argentina. The relations between these variables and their responses to seasonal changes in water temperature were analyzed. A close relationship in seasonal patterns of algal primary production and bacterial secondary production was observed, with the estimated rates of bacterial production similar to that obtained by other authors in eutrophic lakes. Bacterial production was 17 to 46% of the primary production, thus, at 60% assimilation efficiency, the bacterioplankton would consume 28 to 77 % of the total fixed carbon. Seasonal trends in algal primary production and bacterial secondary production were mainly affected by temperature.     

Shell growth of the golden mussel, Limnoperna fortunei (Dunker, 1857) (Mytilidae), in the Río de la Plata, Argentina

The golden mussel, Limnoperna fortunei, is an invasive freshwater bivalve. Since its introduction to Argentina, it had caused damage to the native fauna as well as economic damage to industries of the region. Here, we describe the growth of L. fortunei in a natural temperate environment in Argentina. Age was estimated according to the modal progression method. The constants in the von Bertalanffy growth model were adjusted by an iterative algorithm. Three annual cohorts had similar growth rates. The estimated t ₀ for each cohort showed a temporary displacement in relation to the spawning period.     

Farming,fishing, and fire in the history of the upper Río Negro region of Venezuela

Studies of Río Negro subsistence farming and fishing activities are used to estimate the human carrying capacity for the region and the likely pattern of human land-use during prehistory. Ceramic evidence suggests human presence in the region more than 3000 years ago. Traditional farming is labor intensive and relatively unproductive. Nevertheless, farmers achieve an energy return of 15.21, and produce 2600 kcal per work hour. Fish are the major protein source, but fish catch per unit of effort and fish yield per hectare of floodplain are very low; fishermen are probably exploiting local fish resources very close to their limit. The low human population density would suggest that the Río Negro forest has been relatively undisturbed. Nevertheless, charcoal is widespread and abundant in forest soils. This charcoal is probably from anthropogenic or natural wildfires. These results suggest a much more complex history for Amazonia than previously thought.K. Clark is a free-lance biologist residing in Lima, Peru     

Rôle of the midgut,crop, and maxillae of Bombyx mori in the production of cocoon-digesting enzyme

The rôle of the midgut, crop, and maxillae in the production and utilization of the cocoon-digesting enzyme was investigated in the silkworm, Bombyx mori.About a sixtyfold purified preparation of midgut protease was obtained by ammonium sulphate precipitation and column chromatography.Immunological studies by the agar diffusion method of Ouchterlony revealed that the crop and midgut proteases of the pharate adult are antigenically identical whereas that of the maxillary protease is different.From the results of extirpation experiments and previous studies it was shown that the midgut, crop, and maxillae play important rôles in the escape of moths from their cocoons.     

Assemblages of peracarid crustaceans in subtidal sediments from the Ría de Aldán (Galicia,NW Spain)

Peracarid crustaceans inhabit many marine benthic habitats and are good indicators of environmental conditions. There is, however, a lack of information about diversity and distribution of peracarid crustaceans on the shallow subtidal sediments of the Galician rias. In the summer of 1997, 27 subtidal stations were sampled in the Ría de Aldán, a ria on the southern margin of the mouth of the Ría de Pontevedra (Galicia, NW Spain). A total of 16,191 peracarid individuals were collected, comprising 125 species belonging to five orders. Amphipods were dominant in number of species and individuals, followed by isopods and cumaceans. Multivariate analyses of these data indicated that depth and sediment granulometry were major determinants of distribution and composition of peracarid assemblages in the ria.     

Distribution,status and biology of the tortoise,Geochelone chilensis,in Río Negro Province,Argentina

Morphometric and meristic data from 32 specimens from Río Negro Province do not allow differentiation between G. donosobarrosi and G. chilensis. The significance of morphological and genetic differentiation among Argentinian tortoises is yet to be determined; southern Chaco tortoises undergo ontogenetic and sexual dichromatism. Geochelone chilensis has an extensive latitudinal range (Map 1). Field investigations indicate that Chaco tortoises occupy, and apparently excavate, burrows in the southern portion of the range, prior reports of the species’ southern limit are evaluated and the link between tortoise distribution and “monte”; vegetation is discussed. The season of reproduction and clutch size are noted. Extensive internal pet traffic has markedly affected tortoise populations in some areas; near the southern limit of the range, however, there is little commercial collecting.     

Phonolic components of the primary cell wall and their possible rôle in the hormonal regulation of growth

The insoluble cell wall polymers of cultured spinach cells contained esterified ferulic acid at 2–5 mg g^-1 dry weight. Gibberellic acid (GA₃, 10^-11–10^-6 M) promoted the expansion of these cells and simultaneoulsy suppressed peroxidase secretion, reduced the activity of cellular phenylanine ammonia-lyase and favoured the accumulation of wall-esterified ferulate and of extracellular soluble phenolic aglycones. When growth was prevented with 0·7 M sorbitol, GA₃ still evoked the phenolic and peroxidase effects. It is suggested that peroxidase restricts growth by rigidifying the cell wall in two ways: (a) covalently by catalysing the conversion of feruloyl side-chains into diferuloyl cross-links and (b) non-covalently by catalysing the conversion of soluble phenolics into hydrophobic quinones (or polymers). GA₃ is hypothesised to prevent this rigidification by inhibiting peroxidase secretion.Abbreviations A ₂₈ absorbance at 280 nm - a _1cnt ^1% absorptivity coefficient - 2,4-D 2,4-dichlorophenoxyacetic acid - EtOAc ethylacetate - GA₃ gibberellic acid - mol wt molecular weight - PAL phenylalanine ammonia-lyase - PCV packed cell volume - sh shoulder or inflection - TLC thin-layer chromatography - UV ultra-violet - wavelength - IAA indoleacetic acid     

The primary production of phytoplankton in the restored Maltañski Reservoir in Poland

Patterns in composition, abundance and diversity of the annelid fauna (Polychaeta and Oligochaeta) in 22 sandy beaches in Iceland were explored. The effect of exposure on annelid distribution was studied. A total of 5651 annelids were recorded from 160 core samples. Oligochaetes (chiefly Tubificidae) dominated the annelid assemblage whereas polychaetes represented a minor fraction. Polychaetes were relatively more abundant in exposed than in sheltered beaches, contrary to oligochaetes. Meiofaunal polychaete species were also more abundant in exposed than in sheltered beaches. Southwest beaches seemed more diverse in annelid species than northern ones. Annelid diversity did not differ between sheltered and exposed sites, but higher diversity was attained in fine sands at sheltered areas. Cluster analysis revealed large differences between beaches in the annelid community composition. The general patterns found suggest that beach exposure is a major factor conditioning macro- and meiofaunal polychaete and oligochaete distribution along the Icelandic coast.     

Parameterization of surface irradiance and primary production in Århus Bay,SW Kattegat,Baltic Sea

The aims of the present study were to develop a parameterization of a one-year-long observed PAR time-series, apply the PAR parameterization in a primary production relation, and compare calculated and observed time-series of primary production. The PAR parameterization was applied in the generally used relation for the primary production (P _d): P _d = a(BI ₀ Z ₀) + b with observed photic depth (Z ₀) and Chl-a concentrations (B). It was tested whether the PAR parameterization in combination with this simple relation for primary production was able to describe the actual measured primary production. The study is based on a one year long time-series of PAR, CTD-casts (n = 45), and primary production measurements (n = 24) from Århus Bay (56°09′ N; 10°20′ E), south west Kattegat. Results showed a high and positive correlation between observed and calculated primary production in the bay, as based on the present PAR parameterization combined with the simple primary production relation. The developed PAR parameterization, which calculates total daily surface irradiance per day (M photons m^?2 d^?1), can be applied in any ecological application taking into account that it was developed for the latitude of 56° N.     

Marine primary production in the Canadian Arctic, 1956, 1961�C1963

Marine primary productivity studies pursued in the Canadian Arctic in 1961–1963, using standard techniques (oxygen and carbon-14) of the time, showed that maximum production developed rapidly in July at 5-m depth under very low light intensities and under intact but melting sea ice. The time of maximum production was correlated with depths of snow in spring. Low production levels were found in August in those years and estimated in 1956. Nitrate exhaustion occurred before maximum production and was followed by rapid sinking of chlorophyll and productivity and reduction of assimilation numbers. Gross production values greatly exceeded net production values in 1961–1963, and gross production in 2 years was about double that of a third year, which may be due to different initial conditions of nutrient concentrations in the euphotic zone. Interannual variability in primary production may be the result of changes in water masses in the surface layer, as driven by atmospheric pressure patterns.     

Seasonal changes in adenine phosphoribosyltransferase and adenosine kinase activities as markers of the dormancy and the growth of Fragaria × ananassa

Because of the potential involvement of adenosine in the winter re-acquisition of nucleotide synthesis capability of strawberry plants (Fragaria × ananassa Duch., Elsanta), the properties and the time-course activity of an adenosine kinase (EC 2.7.1.20) and an adenine phosphoribosyltransferase (APRTase, EC 2.4.2.7) of the adenosine recycling pathway were characterized. The results showed an increase in APRTase activity during winter re-acquisition of nucleotide synthesis capability and an increase in adenosine kinase activity during spring growth of strawberry plants. Western blot analysis, performed with polyclonal rabbit antibodies raised against peach bud adenosine kinase, showed a concomitant rise in the strawberry enzyme. These results suggest that APRTase activity could be a good marker of the break of strawberry plant dormancy and adenosine kinase a marker of subsequent spring growth.     

Mechanical aquatic weed management in the lower valley of the Río Negro, Argentina

A major irrigation system in the Lower Valley of the Rió Negro, Argentina, has been invaded by aquatic plants, with Potamogeton illinoensis Morong dominant in irrigation channels and Potamogeton pectinatus L. dominant in drainage channels. Although several other macrophytes are present, problems are largely caused by the dominant species. Results are presented for plant biomass response to weed control treatments using a chain-cutting method in the principal irrigation channel of the system. Peak above-ground biomass of Potamogeton illinoensis was reduced by about 38% by this physical control regime. The treated populations regrew rapidly after spring clearance, but did not regrow after subsequent mid- and late-season clearance operations, even though untreated population biomass remained high during this period. The highest density of Potamogeton illinoensis ramets was found in treated areas. Chain- cutting produced no discernible effect on dissolved oxygen, water temperature, water conductivity, pH or light extinction coefficient compared with untreated check sectors of the channel.     

Modern pollen and vegetation relationships in northeastern Patagonia (Golfo San Matías,Río Negro)

The understanding of modern pollen is a critical component of palaeoecological research. The pollen assemblages reflect general patterns in vegetation distribution; however, pollen representation is biased by several factors such as differences in pollen production, dispersal and preservation. Therefore, this relationship cannot be applied directly in pollen records of the past. The aim is to study the relationship between modern pollen and vegetation and to apply this new information on the interpretation of Holocene pollen records. Classification of the vegetation into groups corresponding to different geomorphological units was carried out by cluster analysis. Discriminant analysis was applied on the surface samples to test if different vegetation types could be distinguished by their pollen assemblages. To evaluate the relationship between pollen assemblages and vegetation types, association (A), under-representation (U) and over-representation (O) indexes were calculated for all present taxa in both plant and pollen dataset. The main vegetation types are reflected in pollen assemblages but with greater differences in the proportions of Poaceae, Hyalis argentea, Chenopodiaceae, Asteraceae subf. Asteroideae and Larrea divaricata. Association and representation indexes provided information related to the production rate and pollen dispersal. This study helps to interpret Holocene vegetation and environmental changes from fossil pollen records of the study area.     

Patterns in the distribution of fish assemblages in Río Amacuzac,Mexico: influence of abiotic factors and biotic factors

Patterns in spatial and seasonal distribution of fish communities were analyzed in the Río Amacuzac, Mexico, and their relationship to environmental variables and habitat characteristics. The PCA biplot of the study sites and environmental factors showed the first two axes accounting for 52.93% of the variance. The diagram showed the study sites ordination in environmental gradients. The first axis explained variables related to habitat characteristics and temperature (36.30%) and second axis arranged the sites in physicochemical and water quality environmental gradients (conductivity, dissolved oxygen, orthophosphates, ammonium, pH) displaying seasonal variation. Fifteen species were recorded, eight of them are exotic. One new record appeared for the Río Amacuzac: Pterygoplichthys disjunctivus is exotic. Study sites with highest species richness were: 5, 7 and 9 (twelve species each one); while the study sites with low species richness were 1, 2, 3 and 6 (eight species each one). Six of the species were distributed throughout the whole river. Based on the composition of the fish fauna, the study sites form two groups and the analysis of fish species displays three groups according to the Bray–Curtis index. The diagram of the canonical correspondence analysis relates environmental parameters to the abundance of fish species and showed that the first two axes exhibit 78.31% of the explained variance. Species richness had a spatial pattern associated to the introduction of exotic species for ornamental uses. According to the results of the importance value index (IVI), the dominant species were the poecilids Poeciliopsis gracilis and Heterandria bimaculata, small fishes that were introduced in the river. Río Amacuzac has a biotic alteration in the structure of fish communities due to the invasion of exotic species, representing risks to the integrity of the native fish fauna.     

Detection of Peptidic Sequences in the Ancient Acidic Sediments of Río Tinto,Spain

Biomarkers are molecules that are produced by or can be associated with biological activities. They can be used as tracers that give us an idea of the ancient biological communities that produced them, the paleoenvironmental conditions where they lived, or the mechanism involved in their transformation and preservation. As a consequence, the preservation potential of molecules over time depends largely on their nature, but also on the conditions of the environment, which controls the decomposition kinetics. In this context, proteins and nucleic acids, which are biomolecules bearing biological information, are among the most labile molecules. In this research, we report the presence of short-chained peptides obtained from extracts of ferruginous sedimentary deposits that have been produced under the acidic and oxidizing solutions of Río Tinto, Spain. These preliminary results go against the paradigmatic idea that considers the acidic and oxidizing environments inappropriate for the preservation of molecular information.     

Evaluation of the cold-active Pseudoalteromonas haloplanktis β-galactosidase enzyme for lactose hydrolysis in whey permeate as primary step of d-tagatose production

d-Tagatose is an innovative natural low-calorie bulk sweetener with a broad potential for low-calorie and low-glycaemic foods and drinks. Production of this healthy sweetener is realized through enzymatic d-galactose isomerization. d-Galactose needs to be produced in situ due to its limited availability. Whey permeate contains a substantial amount of lactose, which is an interesting source for d-galactose production through enzymatic lactose hydrolysis. In this context, the cold-active β-galactosidase from the psychrophile Pseudoalteromonas haloplanktis was studied. Optimal parameters for efficient lactose hydrolysis in whey permeate have been deduced, viz. optimal incubation temperature, pH and lactose concentration. Hydrolysis efficiencies above 96.0% were realized within 24 h at 23 °C and pH 7.0 in whey permeate with a maximum dry matter content of 10.0% (w/w). In addition, the effect of the presence of d-glucose and d-galactose was investigated up to concentrations of 100 g l⁻¹. d-Glucose inhibited lactose hydrolysis more strongly compared to d-galactose. Also, the operational stability of the cold-active β-galactosidase was studied. Hydrolysis efficiencies above 90.0% were maintained during 7 subsequent hydrolysis cycles.     

Immunohistochemical localization of transforming growth factor-α and epidermal growth factor-receptor in the mesonephros and metanephros of the chicken

Summary Transforming growth factor-alpha (TGF-) is a polypeptide related to epidermal growth factor (EGF). Both bind to EGF-receptor (EGF-R) to carry out their function in a variety of tissues and cell lines. Several studies have shown their presence in mammalian kidney, however, nothing has to date been stated concerning their existence in avian kidney. Expression of TGF- and EGF-R is reported here for the first time during the development of the chicken kidney. Using immunohistochemical techniques, we identified a TGF- (but not EGF) in mesonephric distal tubule cells from day 8 to day 20 of embryonic development and in metanephric distal tubule cells from day 14 of embryonic development to the adult. The histochemical characteristics of these cells and their histological localization suggest that they may be the principal cells of the distal tubules. Similarly, EGF-R was found in mesonephric proximal tubule cells from day 7 to day 18 of embryonic development and in metanephric proximal tubule cells from day 13 of embryonic development up to adult stages. The coexistence of both TGF- and EGF-R from the onset of development of mesonephros and metanephros supports their possible role in mechanisms of proliferation and differentiation of the cells of these organs.     

Ecology,morphology and physiology of Chroothece richteriana (Rhodophyta,Stylonematophyceae) in the highly calcareous Río Chícamo,south-east Spain

The ecology of Chroothece was studied in the highly calcareous Río Chícamo, south-east Spain, in order to explain its success there, but rarity elsewhere. The river, which originates mainly from an underground aquifer, has water with high conductivity, sulphate and nitrate but low phosphate concentrations, the latter mainly organic. Chroothece occurs in mats and in lobed colonies reaching 4 cm in the broadest dimension. The colony surface consists of one layer of cells, each of which is attached to a stalk, which dichotomizes when the cell divides; stalks often extend to the colony base. The central region of many mat cells and almost all colony cells has a yellow to orange-brown colour, associated with the numerous lipid droplets densely covering the surface of the pyrenoid and arms of the star-shaped chloroplast. Field material and laboratory isolates indicate that stalk formation occurs under moderate P limitation and both stalks and cell sheath show high phosphatase activities. This also occurred in a culture collection strain maintained for 30 years in a very P-rich medium, but then transferred to a moderately P-limiting medium (c. 0.9 mg l^?1). We suggest that colony formation is initiated by aggregation of motile cells following P pulses in the water. Comparisons are made with Rivularia, a competitor in this nitrate-rich river, in spite of being a N₂-fixer. One difference is that Chroothece cells lie at the periphery of the colonies and are therefore exposed to maximum sunlight, whereas Rivularia trichomes grow inside colonies with photoprotection by scytonemin. However, the ability to withstand heavy grazing pressure may be an especially important factor favouring Rivularia here.