A stirred microchamber for oxygen consumption rate measurements with pancreatic islets

Improvements in pancreatic islet transplantation for treatment of diabetes are hindered by the absence of meaningful islet quality assessment methods. Oxygen consumption rate (OCR) has previously been used to assess the quality of organs and primary tissue for transplantation. In this study, we describe and characterize a stirred microchamber for measuring OCR with small quantities of islets. The device has a titanium body with a chamber volume of about 200 microL and is magnetically stirred and water jacketed for temperature control. Oxygen partial pressure (pO(2)) is measured by fluorescence quenching with a fiber optic probe, and OCR is determined from the linear decrease of pO(2) with time. We demonstrate that measurements can be made rapidly and with high precision. Measurements with betaTC3 cells and islets show that OCR is directly proportional to the number of viable cells in mixtures of live and dead cells and correlate linearly with membrane integrity measurements made with cells that have been cultured for 24 h under various stressful conditions.     

Regulation of glyoxysomal enzymes during germination of cucumber. Temporal changes in translatable mRNAs for isocitrate lyase and malate synthase

The relative levels of translatable messenger RNA for isocitrate lyase and malate synthase were determined in the dry seed and for the first seven days of development of cucumber cotyledons. After extraction and quantification of total and poly(A)-rich RNA each day, the RNA fractions were translated in an optimized wheat germ system and the specific polypeptides were immunoprecipitated quantitatively. The radiolabeled isocitrate lyase and malate synthase polypeptides were then fractionated on dodecylsulphate/polyacrylamide gels, visualized by exposure to X-ray film and quantified densitometrically. The relative levels of translatable messenger RNA for these enzymes rise and fall with a developmental program similar to the enzyme activities, but preceding the latter by about one day. This implies that the rise in enzyme activity is dependent upon a prior postgerminative increase in translatable messenger RNA for the enzymes. These studies also suggest that messenger RNA levels may be regulated, at least in part, by light.     

Hydroxylamine is a vasorelaxant and a possible intermediate in the oxidative conversion of L-arginine to nitric oxide

Our objective was to determine whether hydroxylamine is a possible intermediate in the oxidative conversion of L-arginine to nitric oxide. Vasorelaxation by hydroxylamine is known to be mediated by nitric oxide. The vasorelaxant properties of hydroxylamine were examined using rat aortic rings and an isolated rat lung perfusion model. Hydroxylamine and acetylcholine were equally effective in relaxing norepinephrine-contracted intact aortic rings, whereas only hydroxylamine relaxed aortic rings with endothelium removed. This endothelium-independent vasorelaxation by hydroxylamine indicated that the hydroxylamine-converting enzyme is not localized solely within endothelial cells. Catalase, an enzyme known to oxidize hydroxylamine to nitric oxide, was present in homogenates of intact and endothelium-denuded rings. Cyanamide, another catalase substrate and a known precursor of nitroxyl (HNO), was not a vasorelaxant of aortic rings or of isolated, hypoxia-constricted lungs. These results suggest that free nitroxyl is not an intermediate in the oxidation of hydroxylamine to nitric oxide. An overall pathway for the oxidative conversion of L-arginine through an hydroxylamine intermediate to nitric oxide is proposed.     

Position specificity in Chitonomyces (Ascomycota, Laboulbeniomycetes) on Laccophilus (Coleoptera, Dytiscidae): a molecular approach resolves a century-old debate

The occurrence of Laboulbeniomycete species consistently on a precise portion of beetle integument was investigated in 13 species of Chitonomyces ectoparasitic on the aquatic diving beetle Laccophilus maculosus (Coleoptera, Dytiscidae). The phenomenon was called "position specificity" by Roland Thaxter in 1896, yet the mechanism has remained unknown. By using molecular analysis of the nucSSU rRNA gene and the 5.8S and partial ITS1 rRNA regions, 13 species of Chitonomyces reported to exhibit position specificity on Laccophilus maculosus were placed neatly into pairs of morphotypes, resulting in synonomies and recognition of six phylogenetic species (one species is a triplet). Each phylogenetic species was located at corresponding positions on male and female beetles that make contact during mating. In addition, ecological data and video footage of the mating behaviors of Laccophilus confirmed that sexual transmission is the mechanism behind this enigmatic phenomenon.     

How plants communicate using the underground information superhighway

The rhizosphere is a densely populated area in which plant roots must compete with invading root systems of neighboring plants for space, water, and mineral nutrients, and with other soil-borne organisms, including bacteria and fungi. Root-root and root-microbe communications are continuous occurrences in this biologically active soil zone. How do roots manage to simultaneously communicate with neighboring plants, and with symbiotic and pathogenic organisms within this crowded rhizosphere? Increasing evidence suggests that root exudates might initiate and manipulate biological and physical interactions between roots and soil organisms, and thus play an active role in root-root and root-microbe communication.     

The enzymatic basis for pesticide bioremediation

Enzymes are central to the biology of many pesticides, influencing their modes of action, environmental fates and mechanisms of target species resistance. Since the introduction of synthetic xenobiotic pesticides, enzymes responsible for pesticide turnover have evolved rapidly, in both the target organisms and incidentally exposed biota. Such enzymes are a source of significant biotechnological potential and form the basis of several bioremediation strategies intended to reduce the environmental impacts of pesticide residues. This review describes examples of enzymes possessing the major activities employed in the bioremediation of pesticide residues, and some of the strategies by which they are employed. In addition, several examples of specific achievements in enzyme engineering are considered, highlighting the growing trend in tailoring enzymatic activity to a specific biotechnologically relevant function.     

Divergent compensatory growth responses within species: linked to contrasting migrations in salmon?

Animals often exhibit accelerated or “compensatory” growth (CG) after periods of environmentally induced growth depression, raising important questions about how they cope with environmental variability. We tested an underexplored hypothesis regarding the evolutionary consequences of CG; namely, that natural populations differ in CG responses. Common-garden experiments were used to compare subadult growth following food restriction between groups (control, treatment) of two Atlantic salmon (Salmo salar) populations and their first-generation (F₁) hybrids. The populations are found at similar latitudes but characterized by differences in migration distance. We predicted that long-distance migrants would better maintain growth trajectories following food restriction than short-distance migrants because they: (1) require larger body sizes to offset energetic costs of migration and (2) face greater time constraints for growth as they must leave non-breeding areas earlier to return to breeding areas. Long-distance migrants grew faster, achieved quicker CG (relative to controls), and their overall body morphology was more streamlined (a trait known to improve swimming efficiency) than slower growing short-distance migrants. F₁ hybrids were generally intermediate in “normal” growth, CG, and body morphology. We concluded that CG responses may differ considerably among populations and that the conditions generating them are likely interconnected with selection on a suite of other traits.