Increase in the production of allelopathic substances by Prymnesium parvum cells grown under N- or P-deficient conditions

The haptophyte Prymnesium parvum is known to produce a set of highly potent exotoxins, commonly called prymnesins. These toxins have been shown to have several biological activities, including ichthyotoxic, neurotoxic, cytotoxic, hepatotoxic and hemolytic activity towards a range of marine organisms. In addition, recent studies have shown that the toxicity of P. parvum is enhanced when the cells are grown under N- or P-deficient conditions. In this study, the influence of prymnesium toxins on the growth of other phytoplankton species was investigated by addition of cell-free filtrate of P. parvum cultures grown under nutrient-deficient (N or P) or non-deficient conditions. Addition of cell-free filtrate from P. parvum cultures grown under N or P limitation inhibited the growth of Thalassiosira weissflogii, Prorocentrum minimum and Rhodomonas cf. baltica. In contrast, a strain of Prymnesium patelliferum known to produce prymnesium toxins was not negatively affected under any conditions. Furthermore, addition of filtrates from nutrient-sufficient P. parvum cultures did not negatively influence the growth of any of the tested species. These findings suggest that prymnesium toxins may play an allelopathic role, and that the production of allelopathic substances is regulated by the availability of nutrients.     

The complexity of TGFβ/activin signaling in regeneration

The role of transforming growth factor β TGFβ/activin signaling in wound repair and regeneration is highly conserved in the animal kingdom. Various studies have shown that TGF-β/activin signaling can either promote or inhibit different aspects of the regeneration process (i.e., proliferation, differentiation, and re-epithelialization). It has been demonstrated in several biological systems that some of the different cellular responses promoted by TGFβ/activin signaling depend on the activation of Smad-dependent or Smad-independent signal transduction pathways. In the context of regeneration and wound healing, it has been shown that the type of R-Smad stimulated determines the different effects that can be obtained. However, neither the possible roles of Smad-independent pathways nor the interaction of the TGFβ/activin pathway with other complex signaling networks involved in the regenerative process has been studied extensively. Here, we review the important aspects concerning the TGFβ/activin signaling pathway in the regeneration process. We discuss data regarding the role of TGF-β/activin in the most common animal regenerative models to demonstrate how this signaling promotes or inhibits regeneration, depending on the cellular context.     

Metal-sediment interaction during resuspension

A calibrated shaker was used to resuspend sediments from Hamilton Harbour, Ontario at different shear stresses. The flocs formed by resuspension were irreversible and increased in size and number with increasing shear. Individual particle size was constant at about 0.1 µm for the different flocs and independent of shear, but agglomeration size increased with shear. H-ion exchange as a function of sediment concentration fits a Langmuir type function well. Exchange of total Ba, Ca, Cd, Cr, Cu, Mg, Ni, Pb and Zn with H⁺ were determined for the different shear regimes which covered quiescence to gale conditions. A simple lumped one intrinsic constant and fixed capacitance electrostatic model is used to fit the exchange data for each divalent metal.     

Tackling unresolved questions in forest ecology: The past and future role of simulation models

1. Understanding the processes that shape forest functioning, structure, and diversity remains challenging, although data on forest systems are being collected at a rapid pace and across scales. Forest models have a long history in bridging data with ecological knowledge and can simulate forest dynamics over spatio‐temporal scales unreachable by most empirical investigations.
2. We describe the development that different forest modelling communities have followed to underpin the leverage that simulation models offer for advancing our understanding of forest ecosystems.
3. Using three widely applied but contrasting approaches – species distribution models, individual‐based forest models, and dynamic global vegetation models – as examples, we show how scientific and technical advances have led models to transgress their initial objectives and limitations. We provide an overview of recent model applications on current important ecological topics and pinpoint ten key questions that could, and should, be tackled with forest models in the next decade.
4. Synthesis. This overview shows that forest models, due to their complementarity and mutual enrichment, represent an invaluable toolkit to address a wide range of fundamental and applied ecological questions, hence fostering a deeper understanding of forest dynamics in the context of global change.

Forest models can help understanding the processes that shape forest functioning, structure and diversity, since they can can simulate forest dynamics over spatio‐temporal scales unreachable by most empirical investigations. Here we describe the development of three widely applied but contrasting forest mo−delling approaches — species distribution models, individual‐based models and dynamic global vegetation models. We provide an overview of recent model applications and pinpoint ten key questions that could, and should, be tackled with forest models in the next decade.     

Damaging effects of intense repetitive treadmill running on murine intestinal musculature

Several gastrointestinal symptoms associated with prolonged intense exercise (IE) have been reported, although the mechanisms underlying its effects on the intestine remain poorly understood. The aim of the present study was to investigate whether IE may induce oxidative stress in the intestine, as well as its possible relationship with intestinal signaling impairments, leading to contractile disturbances. C57BL/6 mice were submitted to 4 days (EX.4D) and 10 days (EX.10D) of IE. The daily exercise session consisted of a running session until exhaustion, with the treadmill speed set at 85% of each animal's maximum velocity. The decrease in exhaustion time was exponential, and the reduction in the maximum velocity, as assessed by an incremental test, was higher in EX.4D than in EX.10D animals. The ileum mucosa layer was partially destroyed after 4 days of IE, where 37% and 11% muscle layer atrophies were observed in EX.4D and EX.10D animals, respectively. Ileum contractility was significantly impaired in the EX.4D animal group, with reduced efficacy for carbachol, bradykinin, and KCl signaling associated with a decrease in lipid peroxidation and with no alteration of protein oxidation. Intestinal myocytes from EX.10D animals displayed areas containing structurally disorganized mitochondria, which were associated with increased levels of protein oxidation, without alteration of contractility, except for a reduction in the potency of bradykinin signaling. Finally, no clear relationship between ileum contractility and oxidative stress was shown. Together, these results argue in favor of significant functional, biochemical, and morphological disturbances caused by exercise, thus demonstrating that intestinal tissue is very sensitive to exercise.     

Volatile Production Induced by Penicillium digitatum in Orange Fruit and in Culture

Abstract Production of volatiles was stimulated by the infection of Penicillium digitatum in 'Shamouti oranges. During 7 days of disease development, there was a progressive increase in the emanations of the anaerobic metabolites acetaldehyde, ethanol and ethyl acetate. There was also an increase in other volatiles including methanol, acetone, and ethylene, accompanied by a high production of CO₂. The production of acetaldehyde, ethanol and CO₂ in cultures of P. digitatum was, highest on the first day after inoculation, and decreased as the fungus developed. Ethyl acetate and ethylene increased when sporulation had already begun. Neither acetone nor methanol was found in P. digitatum in vitro. The increase of the volatiles in the infected oranges was due to the host-pathogen interaction and peel lesion.