Denitrifying pathways dominate nitrous oxide emissions from managed grassland during drought and rewetting.

Nitrous oxide is a powerful greenhouse gas whose atmospheric growth rate has accelerated over the past decade. Most anthropogenic N2O emissions result from soil N fertilization, which is converted to N2O via oxic nitrification and anoxic denitrification pathways. Drought-affected soils are expected to be well oxygenated; however, using high-resolution isotopic measurements, we found that denitrifying pathways dominated N2O emissions during a severe drought applied to managed grassland. This was due to a reversible, drought-induced enrichment in nitrogen-bearing organic matter on soil microaggregates and suggested a strong role for chemo- or codenitrification. Throughout rewetting, denitrification dominated emissions, despite high variability in fluxes. Total N2O flux and denitrification contribution were significantly higher during rewetting than for control plots at the same soil moisture range. The observed feedbacks between precipitation changes induced by climate change and N2O emission pathways are sufficient to account for the accelerating N2O growth rate observed over the past decade.

Partial break in tolerance of NKG2A-/LIR-1- single KIR+ NK cells early in the course of HLA-matched, KIR-mismatched hematopoietic cell transplantation.

Natural killer (NK) cell subpopulations from 8 HLA-matched but killer cell immunoglobulin-like receptor (KIR)/HLA-ligand-mismatched patient-donor pairs were analyzed in the course of allogeneic hematopoietic stem cell transplantation (HCT). The patients' post-transplantation NKG2A-/LIR-1- NK cells, which expressed only inhibitory KIRs for which the patient had no HLA class I ligands, showed higher cytotoxic capacity than the NKG2A-/LIR-1- NK cells lacking any inhibitory KIRs that remained tolerant throughout the course of HCT. The NKG2A+ NK cell subpopulations displayed the highest levels of cytotoxic activation, which appeared to be significantly enhanced in comparison with that in allogeneic graft's donors. LIR-1- NK cells were much more frequent after HCT than LIR-1+ NK cells and LIR-1 expression on NKG2A+ or NKG2A- NK cells was associated with significantly lower cytotoxic activities. Thus NKG2A-/LIR-1- NK cells expressing only HLA-mismatched KIRs show a partial break in tolerance in the first year following HCT. The failure to exclude LIR-1+ cells within the NKG2A- NK cell subset in previous studies could explain the earlier conflicting results. Thus systemic immune activation in patients following HCT augments the GvL effect through both increasing overall NK cell activities and partially breaking tolerance of unlicensed NK cells.

Intracytoplasmic Bacteria in Male Germ Cells of Philudoria potatoria L. (Lasiocampidae, Lepidoptera, Insecta)

The fine structure of bacteria, detected in the cytoplasm of spermatogonia, spermatocytes, and spermatids of a Lepidoptera species, Philudoria potatoria L. (Lasiocampidae), was described using transmission electron microscopy of ultrathin sections through testes. The effects of the bacteria on the germ cells were studied in semithin sections using light microscopy and in ultrathin sections using transmission electron microscopy. Larvae of the animal were collected in the field at the same location in two subsequent summers and the picture was very similar in both preparations. We examined a total of five animals and all were infected. The intracytoplasmic bacteria were usually rod-shaped, up to 1.7 µm long, and about 0.5 µm thick. They lay in intracellular cavities of the germ cells and were separated from the host cell by a membrane. The envelope of the bacteria consisted of two thin electron-dense layers interspersed by a transparent zone which represent the plasma membrane and the cell wall, respectively. Thus, the bacteria are most probably gram-negative. When the cells contained a small number of intracytoplasmic bacteria, pachytene spermatocytes and the development and structure of the meiotic spindles appeared regular. A prominent layer of perispindle membranes that is typical of male meiosis in the Lepidoptera (Wolf, 1994) was, however, missing in the infected animals. A low number of bacteria apparently does not interfere with the onset of spermiogenesis and it is possible that the microorganisms are transmitted into the next generation via the male germ line. In contrast, high numbers of intracytoplasmic bacteria result in cell degeneration in late prophase I of meiosis. Under these circumstances, electron-dense bodies formed within the nuclei and the nucleoplasm became transparent. The most prominent event in the cytoplasm was the aggregation of the mitochondria into large clusters. Finally, the nuclear envelope dissolved and the germ cells degenerated. The intracytoplasmic bacteria of P. potatoria are interpreted as parasites.

Preparation of insect chromosomes for immunolabeling.

We describe a method for isolating chromosomes from testes of the desert locust, Schistocerca gregaria, and their subsequent incubation with antibodies directed against chromosomal proteins. The procedure involves hypotonic pretreatment of the germ cells, centrifugation onto coverslips in a cytocentrifuge and immunolabeling, while still unfixed, using a chromatin-stabilizing buffer. In the present case, an antibody specific for the acetylated isoforms of histone H4 was tested. After the antibody treatment, the preparations are fixed using formaldehyde, stained with a DNA-specific fluorescent dye and mounted. Analysis of the preparations revealed good preservation of chromosome structure in prophase spermatogonia and late prophase I spermatocytes. Fully condensed chromosomes were not observed and are probably lost during preparation. The bright fluorescence of the autosomes indicates that the reaction between the antibody against acetylated histone H4 and its chromosomal antigen is not impeded. In contrast, the X univalent remained unstained with the exception of a small terminal band. Thus, cytospin preparations of locust germ cells allow high resolution immunolabeling with antibodies against chromosome-associated proteins.