Interacting Effects of Discharge and Channel Morphology on Transport of Semibuoyant Fish Eggs in Large,Altered River Systems

Habitat fragmentation and flow regulation are significant factors related to the decline and extinction of freshwater biota. Pelagic-broadcast spawning cyprinids require moving water and some length of unfragmented stream to complete their life cycle. However, it is unknown how discharge and habitat features interact at multiple spatial scales to alter the transport of semi-buoyant fish eggs. Our objective was to assess the relationship between downstream drift of semi-buoyant egg surrogates (gellan beads) and discharge and habitat complexity. We quantified transport time of a known quantity of beads using 2–3 sampling devices at each of seven locations on the North Canadian and Canadian rivers. Transport time was assessed based on median capture time (time at which 50% of beads were captured) and sampling period (time period when 2.5% and 97.5% of beads were captured). Habitat complexity was assessed by calculating width∶depth ratios at each site, and several habitat metrics determined using analyses of aerial photographs. Median time of egg capture was negatively correlated to site discharge. The temporal extent of the sampling period at each site was negatively correlated to both site discharge and habitat-patch dispersion. Our results highlight the role of discharge in driving transport times, but also indicate that higher dispersion of habitat patches relates to increased retention of beads within the river. These results could be used to target restoration activities or prioritize water use to create and maintain habitat complexity within large, fragmented river systems.     

Effect of cell concentration on the rheology of glucoamylase fermentation broth

During the process optimisation of glucoamylase production by Aspergillus awamori, cell morphology was controlled at such a state that spore aggregation was completely prevented. Samples from five fermentations on complex media using either glucose or starch as carbon source were characterised with a Bohlin CS rheometer. The experimental data were conveniently described in terms of the power law model.     

High affinity specific antiestrogen binding sites are concentrated in rough microsomal membranes of rat liver

Saturation and competitive binding analyses demonstrated the presence of a high affinity (K_D = 0.92 nM), specific antiestrogen binding site (AEBS) in rat liver microsomes and at least 75% of total liver AEBS was recovered in this fraction. When microsomes were further separated into smooth and rough fractions, AEBS was concentrated in the latter. Subsequent dissociation of ribosomes from the rough membranes revealed that AEBS was associated with the membrane and not the ribosomal fraction. Antiestrogen binding activity could not be extracted from membranes with 1 M KCl or 0.5 M acetic acid but could be solubilized with sodium cholate. These data indicate that AEBS is an integral membrane component of the rough microsomal fraction of rat liver.     

Resource competition and fire‐regulated nutrient demand in carnivorous plants of wet pine savannas

Question: What are the mechanisms by which fire reduces competition for both a short‐lived and a long‐lived species in old‐growth ground‐cover plant communities of wet pine savannas (originally Pinus palustris, replaced by P. elliottii)? Location: Outer coastal plain of southeastern Mississippi, USA. Methods: I reviewed previous competition experiments and proposed a new hypothesis to explain the relationship between fire, competition, and species co‐existence in wet longleaf pine savannas. The first study is about growth and seedling emergence responses of a short‐lived carnivorous plant, Drosera capillaris, to reduction in below‐ground competition and above‐ plus below‐ground competition. The second study deals with growth and survival responses of a long‐lived perennial carnivorous plant, Sarracenia alata, to neighbour removal and prey‐exclusion to determine if a reduction in nutrient supply increased the intensity of competition in this nutrient‐poor system. Results: Fire increased seedling emergence of the short‐lived species by reducing above‐ground competition through the destruction of above‐ground parts of plants and the combustion of associated litter. Prey exclusion did not increase competitive effects of neighbours on the long‐lived species. However, because the experiment was conducted in a year without fire, shade reduced nutrient demand, which may have obviated competition for soil nutrients between Sarracenia alata and its neighbours. Conclusion: Repeated fires likely interact with interspecific differences in nutrient uptake to simultaneously reduce both above‐ground competition and competition for nutrients in old‐growth ground cover communities in pine savannas. Restoration practitioners should consider the possibility that the composition of the plant community is just as important as fire in ensuring that frequent fires maintain species diversity.     

Chitin biosynthesis during pupal development of Drosophila melanogaster and the effect of the lethalcryptocephal mutation

Estimation of chitin deposition in the pupal and adult cuticles of adult Drosophila melanogaster during the pupal period is described. The timing of the periods of chitin deposition is compared with that deduced by previous workers using electron microscopy. The hypothesis that lethalcryptocephal mutant homozygotes are unable to evert their cephalic complexes at pupation because of excess chitin deposition is examined. The data obtained show no evidence that the mutation has any effect on chitin deposition.     

Mechanism of maltal hydration catalyzed by beta-amylase: role of protein structure in controlling the steric outcome of reactions catalyzed by a glycosylase.

Crystalline (monomeric) soybean and (tetrameric) sweet potato beta-amylase were shown to catalyze the cis hydration of maltal (alpha-D-glucopyranosyl-2-deoxy-D-arabino-hex-1-enitol) to form beta-2-deoxymaltose. As reported earlier with the sweet potato enzyme, maltal hydration in D2O by soybean beta-amylase was found to exhibit an unusually large solvent deuterium kinetic isotope effect (VH/VD = 6.5), a reaction rate linearly dependent on the mole fraction of deuterium, and 2-deoxy-[2(a)-2H]maltose as product. These results indicate (for each beta-amylase) that protonation is the rate-limiting step in a reaction involving a nearly symmetric one-proton transition state and that maltal is specifically protonated from above the double bond. This is a different stereochemistry than reported for starch hydrolysis. With the hydration catalyzed in H2O and analyzed by gas-liquid chromatography, both sweet potato and soybean beta-amylase were found to convert maltal to the beta-anomer of 2-deoxymaltose. That maltal undergoes cis hydration provides evidence in support of a general-acid-catalyzed, carbonium ion mediated reaction. Of fundamental significance is that beta-amylase protonates maltal from a direction opposite that assumed for protonating starch, yet creates products of the same anomeric configuration from both. Such stereochemical dichotomy argues for the overriding role of protein structures in dictating the steric outcome of reactions catalyzed by a glycosylase, by limiting the approach and orientation of water or other acceptors to the reaction center.