Ecology: The Science Versus the Myth

This paper describes the foundations of ecology as a science and argues for adherence to scientific principles in the environmental arena. Ecology as a science does not present moral or ethical guidance for societal use in environmental management. Moral, ethical, economic, and political values are integral parts of environmental management, but they are derived outside the realm of science. We emphasize the importance of preserving the power of science as a methodology to acquire objective information separated from societal values. Environmental Risk Assessment is a process that engages and requires both the life and social sciences for successful environmental management.     

Diurnal export and carbon economy in an expanding source leaf of cucumber at contrasting source and sink temperature

Effects of contrasting temperatures of an expanding leaf (source) and of remaining plant parts (sink) on diurnal export and distribution of carbon were studied in seedlings of Cucumis sativus L., cv. Farbio. The time course of the rate of export was calculated by measuring simultaneously the exchange of ¹⁴CO₂ and the amount of ¹⁴C in the source leaf by means of a Geiger-Müller detector using a steady-state labelling technique. In all treatments average export rate during the night (16 h) was maximally 50% of the average rate during the 8-h day. Temperature affected the diurnal course of export via the source leaf and the sink in different ways. At a source leaf temperature of 25 or 30°C export stopped 12 h after start of the night, whereas at 20°C export continued throughout the night. However, the total amount of carbon exported during a 24 h cycle, expressed as a proportion of the amount of carbon assimilated, was the same at source leaf temperatures of 20 or 30°C. Thus source leaf temperature did not affect the distribution of assimilates between source and sink, in contrast to sink temperature. After 24 h at a sink temperature of 30°C, 20% more ¹⁴C was exported to plant parts below the source leaf than with a sink temperature of 20°C, at the expense of carbon remaining in the source. During the day less starch and more structural dry matter was formed at a source leaf temperature of 30°C than at 20°C. After a complete day/night cycle, however, there was no difference between the treatments. Starch was the primary carbon source during the night, and the decline in the rate of export coincided with the depletion of starch. Thus the decline in the rate of export at a source leaf temperature of 25 or 30°C at 12 h after the start of the night was due to the depletion of starch at that time. Similarly, at 20°C export could continue until the end of the night as the starch degradation supplied assimilates during the whole night.     

Export of porin to the outer membrane of the phototrophic bacterium Rhodobacter capsulatus 37B4

Export of porin to the outer membrane of the phototrophic purple bacterium Rhodobacter capsulatus was studied with the use of the uncoupler of the electron transport chain, carbonylcyanide-m-chlorophenylhydrazone (CCCP). The agent reversibly blocked the transport of porin across the cytoplasmic membrane. By means of radioactive labeling and immunoprecipitation, porin was found to occur in two forms: (i) the exported form that was extractable from the outer membrane without disrupting the cells, and (ii) a pre-form with a slightly higher apparent molecular mass which accumulated in the cells during the block of the export process. Proteolysis studies revealed that the preform was highly sensitive to added proteases, whereas the exported form was resistant.Abbreviations CCCP carbonylcyanide-m-chlorophenylhydrazone - DMSO dimethylsulfoxide - EDTA ethylenediamine tetraacetic acid - OMP outer membrane porin; pre-OMP, form of outer membrane porin before export - PAGE polyacrylamide gel electrophoresis - PMSF phenylmethylsulfonyl fluoride - SDS sodium dodecyl sulfate     

Diurnal changes in sucrose phosphate synthase activity in leaves

Studies were conducted to identify and compare diurnal changes in sucrose phosphate synthase (EC 2.4.1.14) activity in leaves of different species, and the effect of nitrogen nutrition on the rhythm in soybean [ Glycine max (L). Merr] leaves. In recently expanded corn ( Zea mays L.) leaves, a single peak of enzyme activity was observed at the beginning of the photoperiod. A similar pattern was observed in older corn leaves, but activities (leaf fresh weight basis) were lower. In recently expanded pea ( Pisum sativum L.) and soybean leaves, two peaks of sucrose phosphate synthase activity were observed over a 24-h light:dark period, one at the beginning and one at the end of the photoperiod. A similar pattern was observed in older soybean leaves, but activities were generally lower and the amplitude of the changes was reduced. In a separate experiment, soybean plants were grown in the greenhouse with either 2 or 10 m M nitrate. The high-N plants had higher rates of photosynthesis and translocation, and greater activities of sucrose phosphate synthase in leaf extracts, compared to low-N plants. Over both experiments with soybeans, changes in sucrose phosphate synthase activity during the photoperiod were closely aligned with changes in translocation rate.     

Confidence Estimation of an Unknown Component of the Vector of Regressor Variables in Multivariate Linear Regression

The model used in this paper is Y = Xβ, where with unknown x₀. Estimators of x₀ are derived by putting β_mx₀ =β_m+1 regarding β_m+1 as a new unknown parameter. Formally we use the model Y = X₁β₊ + e where β′₊ = (β₀, …β_m+1 and Then β_m+1/ β_m is a point estimator of x₀. Assuming normality for e and taking the random variable z=β_mx₀?β_m+1 we get a t-distributed variable and finally a confidence estimator of x₀. The formulas are applied in dose response relations in antibiotic assays refering to a standard. Now we can take into account not only the dependence on the dose/concentration but also on the position on the test agar plate where the test solution is filled in. As a consequence the confidence interval of the unknown dose/concentration x₀ becomes shorter and by it the statements more precise.     

The aspartyl protease TgASP5 mediates the export of the Toxoplasma GRA16 and GRA24 effectors into host cells

Toxoplasma gondii and Plasmodium species are obligatory intracellular parasites that export proteins into the infected cells in order to interfere with host‐signalling pathways, acquire nutrients or evade host defense mechanisms. With regard to export mechanism, a wealth of information in Plasmodium spp. is available, while the mechanisms operating in T. gondii remain uncertain. The recent discovery of exported proteins in T. gondii, mainly represented by dense granule resident proteins, might explain this discrepancy and offers a unique opportunity to study the export mechanism in T. gondii. Here, we report that GRA16 export is mediated by two protein elements present in its N‐terminal region. Because the first element contains a putative Plasmodium export element linear motif (RRLAE), we hypothesized that GRA16 export depended on a maturation process involving protein cleavage. Using both N‐ and C‐terminal epitope tags, we provide evidence for protein proteolysis occurring in the N‐terminus of GRA16. We show that TgASP5, the T. gondii homolog of Plasmodium plasmepsin V, is essential for GRA16 export and is directly responsible for its maturation in a Plasmodium export element‐dependent manner. Interestingly, TgASP5 is also involved in GRA24 export, although the GRA24 maturation mechanism is TgASP5‐independent. Our data reveal different modus operandi for protein export, in which TgASP5 should play multiple functions.     

River corridor plants revisited: What drives their unique distribution patterns?

The phenomenon whereby some plant species display a river corridor distribution pattern has long been recognized but is still poorly understood. The goals of this study were to supplement the list of river corridor plants for Central Europe, analyse their habitats and compare their ecological features with those of their widely distributed counterparts. The ATPOL (Atlas of Poland) database was used to compile a list of river corridor plants of Poland and calculate their river corridor-specificity indices (RCSIs). The Ellenberg indicator values, dispersal modes and life forms of river corridor and widely distributed species were compared using generalized linear mixed models (GLMMs). Eighty-five species were classified as river corridor species. The most numerous habitat groups were meadow species (19%), wet-habitat therophytes (15%), riverside tall herbs (13%) and species of dry, sandy soils (12%). These species had mostly requirements for a higher temperature and alkalinity than widespread species. Among river corridor plants, there were a few eurytopic species. Corridor species had usually only one life form and less dispersal modes than widespread species. Hence, specific demands of corridor plants and lower phenotypic plasticity may explain their restricted geographical distribution. The definition of the river corridor plant species needs modification.