Isolation and Characterization of the Putative Photoreceptor for Phototaxis in Amoebae of the Cellular Slime Mold,Dictyostelium discoideum

Amoebae of the cellular slime mold Dictyostelium discoideum (strain AX2) produce a pigment with an absorption spectrum that closely resembles the action spectrum for phototaxis. The protein-pigment complex was isolated and purified by sucrose gradient centrifugation, fast protein liquid chromatography (FPLC) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE). It is tightly membrane-bound and the bulk of it is located in the mitochondrial membrane fraction, while a small part is located in the cytoplasmic membrane fraction, as indicated by marker enzyme tests (succinate dehydrogenase for mitochondria and alkaline phosphatase for the cytoplasmic membrane). It is speculated that the pigment bound to the cytoplasmic membrane acts as photoreceptor and that bound to the mitochondria operates as a shading pigment in the light direction perception mechanism of Dictyostelium amoebae.     

Sorption of hydrophobic organic contaminants and trace metals on phytoplankton and implications for toxicity assessment

The partitioning of trace metals and hydrophobic organic contaminants to phytoplankton determines their toxicity as well as their fate and transport in aquatic ecosystems. Accurate impact assessments, therefore, depend on a good understanding of the factors regulating the sorption of these compounds to biotic particles. The accumulation of chlorinated organic compounds in phytoplankton is generally considered as being due solely to physical sorption, described by reversible equilibrium models based on Langmuir or Freundlich isotherms. On the other hand, the uptake of trace metals is a two phase process: a fast sorption component viewed as an ionexchange or a covalent bonding process with cell surface ligands, followed by an intracellular transport phase that is dependent on cellular metabolic activity. The uptake of inorganic and hydrophobic organic pollutants and their bioaccumulation are influenced in a complex manner by duration of exposure and cell density, by environmental factors such as pH, the concentration of cations and of dissolved and colloidal organic matter, as well as by phytoplankton physiological condition. High concentrations of H⁺, Ca²⁺, and Mg²⁺ ions will reduce trace metal sorption by directly competing for uptake sites on the cell's surface, whereas the presence of dissolved organic carbon such as natural and synthetic chelators and phytoplankton exudates will reduce the bioavailability of both trace metals and hydrophobic organic contaminants. Thus, the impact of toxic contaminants on phytoplankton may be determined as much by the factors influencing uptake and partitioning as by the potency of the toxicants and interspecies differences in sensitivity. Recommendations for improving toxicity assessments are presented.     

The effect of trophic/contaminant interactions on chironomid community structure and succession (Diptera: Chironomidae)

The effects of contaminants and organic pollution on the chironomid communities of two basins in Lac St. Louis, a river-lake on the St. Lawrence River above Montreal, Quebec, were assessed and compared using lake classification theory techniques and morphological deformity indices based on the ligulae and antennae ofProcladius, the dominant surviving component of the south-shore communities. Contaminants from the industrial complex around Beauharnois, Quebec, have seriously degraded communities along the south-shore gradient while the introduction of untreated domestic wastes from Laprairie, Quebec, has seriously affected the communities of the Laprairie basin. The interaction between trophic and contaminant effects constitutes a classic example of the setback or deflection in the trajectory of ecological succession in biological communities hypothesized by ODUM (1981, 1985).     

Response of cabbage head weight to simulated Lepidoptera defoliation

Studies were conducted to determine the effects of continuous constant amounts of artificial defoliation through the preheading and heading growth stages on head weight of cabbage. High levels of continuous artificial defoliation caused a reduction in head weight in all three years of the study, but the highest yield was always attained at some low level of preheading or heading defoliation. These results demonstrate that cabbage is tolerant to some levels of continuous defoliation before and after head formation. Results from this study are incorporated into a cost-benefit analysis to estimate an economic threshold.

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Résumé L'étude a porté sur le poids des pommes de choux (Brassica oleracea) soumis à différentes intensités de défoliations répétées avant et pendant la formation des pommes. Pendant les trois années de l'étude, huit intensités de défoliation continue ont réduit le poids des pommes, mais le poids le plus élevé a toujours été obtenu avec une faible défoliation avant et pendant la formation des pommes. Ceci montre que le chou tolère une certaine défoliation avant et pendant la formation des pommes. Les résultats de cette étude ont été utilisés dans une analyse coût-bénéfice pour estimer le seuil économique de défoliation.

     

Organic acids from the anaerobic decomposition of Agropyron repens rhizomes

Phytotoxicity originating from the anaerobic decomposition of couch grass rhizomes has been studied. Short chain aliphatic (acetic, propionic and butyric) acids appear to be mainly responsible but hexanoic, succinic, phenylacetic, cinnamic, p-coumaric, 4-hydroxyphenylpropionic and 3,4-dihydroxyphenylpropionic acids are also present in the phytotoxic solutions formed during the decomposition.     

Vergleichende Karyologie der Gräser-SubtribenAristaveninae undAirinae (Poaceae — Aveneae)

The chromosome numbers of nearly all species of the grass subtribesAristaveninae andAirinae from Europe and northern Africa are presented. Among theAristaveninae the genusAristavena has 2n = 14 chromosomes, whereasDeschampsia forms a polyploid series with the basic number x = 13. In the subtribeAirinae the basic number x = 7 predominates.Avenella includes a polyploid series up to dekaploidy, whilst the lowest diploid value so far known in grasses — caused by descending dysploidy — exists in the annual generaAiropsis andPeriballia with 2n = 8.From both subtribes 12 different karyotypes are described and depicted as idiograms. The basic karyotypes ofCorynephorus, Periballia andVahlodea differ from each other by different chromosome length. SAT-chromosomes in theAirinae vary somewhat. Some marker chromosomes eludicate phylogenetic relationships. Amphiplasty appears in various genera and was studied particularly in the amphidiploidAira caryophyllea. Karyological and genomatic trends are considered in relation to evolutionary strategies of annuals and perennials.The nuclear DNA content of some species has been determined cytophotometrically. In subtribeAirinae a positive correlation exists between chromosome volume, pollen diameter, and DNA content. A comparison of the duration of microsporogenesis and microgametogenesis in annual and perennial species with their nuclear DNA content has shown that a primary nucleotypic influence is not recognizable.

     

Upper limit on translational diffusion of visual pigment in intact unfixed barnacle photoreceptors

Translational diffusion of pigment molecules in the disc membranes of amphibian rod outer segments is in the range of 10 /10 s. Recently, Goldsmith and Wehner set an upper limit of 10 /20 min to the diffusion in isolated formaldehyde-fixed rhabdoms of crayfish. We have now used the early receptor potential (ERP) to study the diffusion in intact, unfixed barnacle photoreceptors. The ERP from a cell fully adapted to blue light (most of the pigment in the rhodopsin state) was changed by 8–22% of its maximum change when the pigment in a 30 m spot was (almost) completely shifted to the metarhodopsin state by red laser adaptation. Further red illumination of the same spot 30 min later produced only a limited further change in the ERP (attributable to light scatter), showing that R had not migrated into the spot. It is concluded that the visual pigment diffuses by less than 30 /30 min.Based on material presented at the European Neurosciences Meeting, Florence, September 1978     

Tissue microenvironment and the genetic control of hair pigment patterns in mice

This study was conducted to assess microenvironmental variability within integumental tissue of genetically identical mice with respect to a specific cellular response: cyclic synthesis of yellow and black pigment by hair bulb melanocytes. Crosses were performed within and between inbred strains of mice that were isogenic with the exception of a single gene substitution at the agouti locus. Agouti locus genes included the A^vy, A^w, A, a^td, a^t, a^x, a^m, and a alleles. The pigment patterns of dorsal, flank, and ventral hairs of the first and third hair generations and of hairs growing in special integumentary areas such as the pinna, tail, and hind foot were studied. It was found that the amount of yellow pigment synthesized by hair bulb melanocytes within genetically identical mice is both agedependent and conditioned by the integumentary environment. Furthermore, the special integumentary regions produce hairs with a variety of pigment patterns in which the distribution and relative amounts of black and yellow pigments do not necessarily conform to dominance relationships expected among agouti locus alleles as judged by their effects on the pigmentation of the dorsal pelage. We conclude that within genetically uniform integumental tissues, microenvironmental differences occur and are reflected as alterations in the metabolic pattern of differentiated cells.     

Pond Acoustic Sampling Scheme: A draft protocol for rapid acoustic data collection in small waterbodies

1. Freshwater conservation is vital to the maintenance of global biodiversity. Ponds are a critical, yet often under‐recognized, part of this, contributing to overall ecosystem functioning and diversity. They provide habitats for a range of aquatic, terrestrial, and amphibious life, often including rare and declining species.
2. Effective, rapid, and accessible survey methods are needed to enable evidence‐based conservation action, but freshwater taxa are often viewed as “difficult”—and few specialist surveyors are available. Datasets on ponds are therefore limited in their spatiotemporal coverage.
3. With the advent of new recording technologies, acoustic survey methods are becoming increasingly available to researchers, citizen scientists, and conservation practitioners. They can be an effective and noninvasive approach for gathering data on target species, assemblages, and environmental variables. However, freshwater applications are lagging behind those in terrestrial and marine spheres, and as an emergent method, research studies have employed a multitude of different sampling protocols.
4. We propose the Pond Acoustic Sampling Scheme (PASS), a simple protocol to allow a standardized minimal sample to be collected rapidly from small waterbodies, alongside environmental and methodological metadata. This sampling scheme can be incorporated into a variety of survey designs and is intended to allow access to a wide range of participants, without requiring complicated or prohibitively expensive equipment.
5. Adoption of this sampling protocol would enable consistent sound recordings to be gathered by researchers and conservation organizations, and allow the development of landscape‐scale surveys, data sharing, and collaboration within an expanding freshwater ecoacoustic community—rather than individual approaches that produce incompatible datasets. The compilation of standardized data would improve the prospects for effective research into the soundscapes of small waterbodies and aid freshwater conservation efforts.