Role of interaction zones between surface and ground waters in DOC transport and processing: considerations for river restoration

• 1 A study of dissolved organic carbon (DOC), nitrates and total dissolved phosphorus (TDP) concentrations, conductivity and bacterial numbers was undertaken in subsurface water of the Garonne River (France) under low-flow conditions. The velocity of subsurface flow through a 300-m gravel bar, during this study, was less than 43 m day^?1. DOC, nitrates and TDP concentrations, conductivity and bacterial numbers fluctuated within the gravel bar with no discernible spatial pattern. Bacterial abundance was correlated with DOC concentration. Results were compared to a previous study of the Stillaguamish River (U.S.A.) (Vervier & Naiman, 1992).
• 2 These studies provide evidence that gravel bars are important in the processing of DOC by bacteria in the subsurface water. Bacterial activity is, in turn, determined by sources of DOC from upstream at high discharge, and by patchy local microhabitats at low discharge.
• 3 Restoration of rivers should incorporate, wherever possible, meanders with associated gravel bars and riffles. These will improve DOC-processing capacity, in addition to other benefits predicted by the Building Block Model (Petersen, Petersen & Lacoursière, 1992).

     

Cultured Human Melanocytes Respond to MSH Peptides and ACTH

Although the administration of melanocyte-stimulating hormone (MSH) peptides results in skin darkening in man, cultured human melanocytes have been reported to be unresponsive to these peptides. This may be a consequence of the conditions under which the cells were maintained in vitro, particularly the use of phorbol esters and cholera toxin as melanocyte mitogens. By culturing the cells in the absence of these additives, we demonstrate that α-MSH and its synthetic analogue Nle⁴DPhe⁷α-MSH (NDP-MSH) induce dose-related increases in melanin content and tyrosinase activity and affect cell morphology in the majority of human melanocyte cultures. In addition, NDP-MSH induces increases in tyrosinase mRNA and tyrosinase-related protein-1 (TRP-1) mRNA. The dose-response curves for the MSH peptides are sigmoidal and the two peptides are equipotent in their effects on human melanocytes. Adrenocorticotropic hormone (ACTH) also affects morphology and stimulates melanogenesis and tyrosinase activity in human melanocytes. However, the dose-response curves for ACTH are biphasic, and the melanocytes respond to lower concentrations of ACTH than MSH peptides, similar to those normally present in human plasma. These findings may be important in understanding the role of these pro-opiomelanocortin peptides in human skin pigmentation.     

The Mechanism of Anterior-Posterior Polarity Control in Planarians

The substance which inhibits brain formation in the regenerating planarian Dugesia etrusca was found to be a large molecule, at least in part protein, which electrophoreses as an electronegative moiety in pH 6.8 buffer. A model is presented, based on this finding and previous studies, which proposes an electrochemical mechanism for the control of polarity and possibly for the maintenance of tissue organization in planarians. It is proposed that a bioelectric field exists and moves the electronegative brain-inhibiting substance in a posterior direction, establishing polarity. This model explains the polarity reversal experiments using external fields and many of the previously unexplained classical planarian experiments. Data are presented demonstrating the existence, magnitude, and polarity of this bioelectric field, which is not greatly altered upon decapitation, all in accord with predictions of the model.     

Saline stress tolerance partly matches with habitat preference in ground‐living wolf spiders

Salinity interacts with many physiological functions and therefore probably influences the distribution of terrestrial fauna in tidal flooded salt marshes. The present study tests the hypothesis that the physiological tolerance of stenotopic wolf spiders for saline conditions at least partially determines their occurrence throughout salt‐marsh and nonsaline habitats. The duration of survival of three stenotopic wolf spider species (Araneae: Lycosidae) with different habitat preferences is compared in a controlled laboratory experiment. The forest‐dwelling Pardosa saltans, the salt‐marsh resident Pardosa purbeckensis and its sister species the inland‐living Pardosa agrestis are exposed to experimental conditions with different levels of salinity. Individuals (45 males and 20–45 females per treatment) are placed in individual air‐tight boxes filled with water‐saturated sand. Three levels of salinity are tested: nonsaline (0‰), medium saline (33–35‰) and highly saline (66–70‰). Contents of carbon, hydrogen and nitrogen and the molar ration carbon/nitrogen remain constant over time and do not differ among salinity treatments, indicating that starvation effects on survival, if any, are similar for all treatments. Conversely, body water significantly decreases over time and differs among salinity treatments, in accordance with patterns of survival. Conforming to their habitat preference, the survival of P. saltans and P. agrestis decreases quickly under highly saline conditions. Pardosa purbeckensis, however, has a high survival under both saline and nonsaline conditions. The duration of survival of females is significantly lower than that of males of P. saltans and P. purbeckensis. Durations of survival of ground‐living wolf spiders exposed to salinity partly match their habitat distribution but do not explain the restriction of salt‐marsh species to saline habitats.     

Sexual and Asexual Development of Cryptosporidium parvum in Five Oocyst– or Sporozoite-Infected Human Enterocytic Cell Lines

ABSTRACT. The human enterocytic cell lines Caco-2, HT29, HCT8 and the Caco-2 clones TC7 and PF11 were studied for their ability to support Cryptosporidium parvum development. Following the addition in cultures of either oocysts or excysted sporozoites, immunofluorescent and transmission electron microscopy revealed the presence of all stages of the parasite life cycle by both procedures, and no difference in the ration of infected cells was found among cell lines. More oocysts were seen in cell monolayers infected with oocysts than with sporozoites (p < 0.0001). The number of meronts observed was the same after either oocysts or sporozoites inoculation. Data suggest that the two methods yield a same cell infection rate.