Stability of dissolved and soluble Fe(II) in shelf sediment pore waters and release to an oxic water column

Shelf sediments underlying temperate and oxic waters of the Celtic Sea (NW European Shelf) were found to have shallow oxygen penetrations depths from late spring to late summer (2.2–5.8 mm below seafloor) with the shallowest during/after the spring-bloom (mid-April to mid-May) when the organic carbon content was highest. Sediment porewater dissolved iron (dFe, <0.15 µm) mainly (>85%) consisted of Fe(II) and gradually increased from 0.4 to 15 μM at the sediment surface to ~100–170 µM at about 6 cm depth. During the late spring this Fe(II) was found to be mainly present as soluble Fe(II) (>85% sFe, <0.02 µm). Sub-surface dFe(II) maxima were enriched in light isotopes (δ⁵⁶Fe ?2.0 to ?1.5‰), which is attributed to dissimilatory iron reduction (DIR) during the bacterial decomposition of organic matter. As porewater Fe(II) was oxidised to insoluble Fe(III) in the surface sediment layer, residual Fe(II) was further enriched in light isotopes (down to ?3.0‰). Ferrozine-reactive Fe(II) was found in surface porewaters and in overlying core top waters, and was highest in the late spring period. Shipboard experiments showed that depletion of bottom water oxygen in late spring can lead to a substantial release of Fe(II). Reoxygenation of bottom water caused this Fe(II) to be rapidly lost from solution, but residual dFe(II) and dFe(III) remained (12 and 33 nM) after >7 h. Iron(II) oxidation experiments in core top and bottom waters also showed removal from solution but at rates up to 5-times slower than predicted from theoretical reaction kinetics. These data imply the presence of ligands capable of complexing Fe(II) and supressing oxidation. The lower oxidation rate allows more time for the diffusion of Fe(II) from the sediments into the overlying water column. Modelling indicates significant diffusive fluxes of Fe(II) (on the order of 23–31 µmol m^?2 day^?1) are possible during late spring when oxygen penetration depths are shallow, and pore water Fe(II) concentrations are highest. In the water column this stabilised Fe(II) will gradually be oxidised and become part of the dFe(III) pool. Thus oxic continental shelves can supply dFe to the water column, which is enhanced during a small period of the year after phytoplankton bloom events when organic matter is transferred to the seafloor. This input is based on conservative assumptions for solute exchange (diffusion-reaction), whereas (bio)physical advection and resuspension events are likely to accelerate these solute exchanges in shelf-seas.     

Influence of incubation in seminal plasma on subsequent metabolic and morphological characteristics of bovine spermatozoa

Incubation of bovine spermatozoa at 25° C for up to 8 hours in seminal plasma had little influence on oxygen uptake as compared to preincubation values but increased both the number of dead spermatozoa and proportion of spermatozoa with detached acrosomes. Washing spermatozoa and resuspension in either saline or seminal plasma followed by incubation for 4 or 8 hours decreased oxygen uptake and at 8 hours decreased the proportion of cells with deteched acrosomes as compared to 8 hour control values. When spermatozoa were not washed but were extended in egg yolk citrate extender or seminal plasma, oxygen uptake was greater for cells extended with seminal plasma. Storage of spermatozoa for 14 days at ?196° C following incubation in seminal plasma showed little influence of incubation time in seminal plasma on postfreeze metabolic or morphological characteristics. These experiments indicate that incubation of spermatozoa in seminal plasma prior to storage has little beneficial effect and, on the contrary, may cause an increase in acrosomal loss.     

Genomic instability in interspecific cell hybrids III. Repression of Colcemid resistance in hybrids suggests preferential β-tubulin expression

A Colcemid-resistant Chinese hamster line with an altered form of β-tubulin was used in studies of the expression of spindle proteins in interspecific cell hybrids. Eight hybrids between this line, and a Colcemid-sensitive mouse cell line, were studied. The altered hamster β-tubulin was not expressed as an increased resistance to Colcemid in any hybrid. Since the complete hamster chromosome complement was represented among the hybrids, the absence of altered β-tubulin is not due to segregation of the mutant hamster β-tubulin gene. We suggest either that the hamster β-tubulin gene is repressed in hybrids, or that hamster β-tubulin is excluded from the spindle in hybrid cells. We compare these findings with previous reports of the repression of other highly active, moderately repeated constitutive genes in interspecific hybrids.     

Fusion and hybridization of marsupial and eutherian cells. Heterokaryon formation

Marsupial x eutherian cell hybrids would be very useful for studies of mammalian genetics and cell biology. A critical step in the formation of such hybrids is the fusion of cells to form heterokaryons. We have examined many different combinations of marsupial and eutherian cells for their ability to fuse, and we have found that all combinations yielded heterokaryons, but with different frequencies, depending on the cell types used. Ranked in order of decreasing ability to fuse with eutherian cells, the marsupial cell types were; established lines, primary diploid fibroblasts and lymphocytes. In all fusion experiments there was a marked preference for the formation of homokaryons compared with heterokaryons. It was possible to control the numbers and types of heterokaryons formed by varying the input ratio of parental cells.     

Pneumocystis antigen appearance during immunosuppression

The sequential appearance of Pneumocystis carinii (Pc) antigens during the progression of immunosuppression in rats was studied using the immunoblotting technique and specific immunologic probes. Putative Pc soluble antigens, with molecular weights of approximately 70 and 90 kd, were detected as early as 2 wk after initiation of immunosuppression in rats using a pool of monoclonal antibodies produced to Pc isolated from lungs using enzymatic digestion. Monoclonal antibodies produced to Pc isolated by massaging the lung tissue using a Stomacher apparatus and infection-derived sera did not detect soluble antigens until at least the 6th wk of immunosuppression. Analysis of Pc pellets obtained from Stomacher- and lavage-processed lungs revealed that the lower molecular weight antigens (less than or equal to 40, 45 and possibly 55-60 kd) were recognized early during the immunosuppression process.     

DNA synthesis in U-2 OS human osteosarcoma cells is independent of PDGF binding to functional cell surface receptors

Previous studies have shown that suramin reveals specific PDGF binding sites on U-2 OS human osteosarcoma cells. Studies presented here indicate that U-2 OS cells pretreated with suramin internalize and degrade 125I-PDGF and respond to PDGF by increased tyrosine kinase activity and amino acid transport. However, DNA synthesis in these cells is not reduced by incubation with the PDGF blocking agent suramin and is not stimulated by exogenous PDGF. These data indicate that U-2 OS cells possess functional PDGF receptors but that high levels of DNA synthesis in these cells is unrelated to the binding of secreted PDGF to these cell surface receptors. Thus, it is unlikely that the PDGF mitogen produced by U-2 OS cells stimulates proliferation through an autocrine mechanism involving secretion and subsequent binding to PDGF receptors.     

The origin and function of the mammalian Y chromosome and Y-borne genes – an evolving understanding

Mammals have an XX:XY system of chromosomal sex determination in which a small heterochromatic Y controls male development. The Y contains the testis determining factor SRY, as well as several genes important in spermatogenesis. Comparative studies show that the Y was once homologous with the X, but has been progressively degraded, and now consists largely of repeated sequences as well as degraded copies of X linked genes. The small original X and Y have been enlarged by cycles of autosomal addition to one partner, recombination onto the other and continuing attrition of the compound Y. This addition–attrition hypothesis predicts that the pseudoautosomal region of the human X is merely the last relic of the latest addition. Genes (including SRY) on the conserved or added region of the Y evolved functions in male sex determination and differentiation distinct from the general functions of their X-linked partners. Although the gonadogenesis pathway is highly conserved in vertebrates, its control has probably changed radically and rapidly in vertebrate – even mammalian – evolution.