Mutagenicity of organophosphorus compounds in bacteria and drosophila

140 Organophosphorus compounds (OP's) have been tested for mutagenic activity in bacteria, principally by using two specially constructed sets of tester strains of the bacteria Salmonella typhimurium and Escherichia coli. It was found that 20% gave positive mutagenic responses and that this group of chemicals produce base substitutions rather than frame-shift mutations. In most cases the DNA repair genes exrA⁺ and recA⁺ were for mutagenic activity.Seven compounds were further tested in Drosophila melanogaster for the ability to induce recessive lethal mutations. In some of these cases the doses administered to the flies had to be very low due to the highly toxic nature of the compounds. To overcome this problem, the accumulation of recessive lethal mutations was measured in populations which were continually exposed to the compounds over a period of some 18 months. During this time the populations developed increased resistance to the compound and so the dose administered could gradually be increased. Six of the compounds were mutagenic.Of the compounds tested in both systems, those showing mutagenic activity in bacteria were also mutaganic in Drosophila, those mutagenic in bacteria were not mutagenic in Drosophila.     

Penetration of soil aggregates of finite size

Summary Maximum penetrometer pressure was measured on artificial soil aggregates of finite size (2–29 mm) using blunt probes (total cone angle 60°) driven at 3 mm min⁻¹. Maximum penetrometer pressure increased asymptotically with increase in dimensionless aggregate radius,b/a, wherea andb are the probe and aggregate radii, respectively. A theory was developed for penetration of blunt probes into soil aggregates of finite size. The theory assumed that plastic failure occurs out to a radius,R, and that beyond this only elastic straining occurs. This theory can be applied to estimate the radial and tangential stresses adjacent to a blunt probe. The estimated radial and tangential stresses increased with increase in dimensionless aggregate radius,b/a. The radius of the plastic front,R, around the probe is predicted to increase with increased aggregate size. The results also demonstrate the effect of soil shear cohesion and internal friction angle onR. The results are discussed with reference to root penetration.     

Determination of imipramine in plasma by high pressure liquid chromatography and field ionization mass spectrometry: increased sensitivity in comparison with gas chromatography mass spectrometry

A quantitative method is reported for the determination of imipramine in plasma samples in the low nanogram and subnanogram range. The sensitivity and precision of the technique, which involves high pressure liquid chromatography and direct probe field ionization mass spectrometry, are approximately an order of magnitude greater than are offered by gas chromatography mass spectrometry with selected ion monitoring using deuterated or other types of internal standards. [2H6]Imipramine, labeled in the ethylene bridge and in the aromatic rings, serves as the isotopic diluent. The method has been used for the determination of the comparative bioavailabilities of two different commercial preparations of imipramine. In these tests, subjects ingested a 25 mg tablet of one or the other drug preparation together with a solution containing an equivalent amount of imipramine deuterated in the ethylene bridge ([2H2]imipramine). The latter served as an internal check for intrasubject variability in absorption of the imipramine tablets. Typical results from one of the subjects are presented.     

Evolutionary Relationships between Rhynchosporium lolii sp. nov. and Other Rhynchosporium Species on Grasses

The fungal genus Rhynchosporium (causative agent of leaf blotch) contains several host-specialised species, including R. commune (colonising barley and brome-grass), R. agropyri (couch-grass), R. secalis (rye and triticale) and the more distantly related R. orthosporum (cocksfoot). This study used molecular fingerprinting, multilocus DNA sequence data, conidial morphology, host range tests and scanning electron microscopy to investigate the relationship between Rhynchosporium species on ryegrasses, both economically important forage grasses and common wild grasses in many cereal growing areas, and other plant species. Two different types of Rhynchosporium were found on ryegrasses in the UK. Firstly, there were isolates of R. commune that were pathogenic to both barley and Italian ryegrass. Secondly, there were isolates of a new species, here named R. lolii, that were pathogenic only to ryegrass species. R. lolii was most closely related to R. orthosporum, but exhibited clear molecular, morphological and host range differences. The species was estimated to have diverged from R. orthosporum ca. 5735 years before the present. The colonisation strategy of all of the different Rhynchosporium species involved extensive hyphal growth in the sub-cuticular regions of the leaves. Finally, new species-specific PCR diagnostic tests were developed that could distinguish between these five closely related Rhynchosporium species.     

Analysis of a 5S RNA-protein complex isolated from the ribosomes of rye embryos

Rye embryo ribosomes were dissociated into subunits and the large subunit fraction was treated with formamide. A low molecular weight complex of RNA and protein (RNP) was released. Electrophoresis of the RNP in polyacrylamide gels containing sodium dodecyl sulphate yielded an RNA band and a single protein band. The protein had a molecular weight of approximately 41 000 and the RNA of the complex was shown to be 5S ribosomal RNA. Embryos were germinated in the presence of [32P]orthophosphate and the labelled RNP was isolated from their ribosomes. The RNA component was partially digested with pancreatic A ribonuclease and the parts protected from degradation by the protein were determined by sequence analysis. Although the whole 5S RNA molecule was shielded to some extent, the portion most protected was between nucleotides 68 and 108. This is, therefore, probably the part of plant cytosol 5S RNA which is primarily involved in the interaction with protein in the complex and possibly in the ribosome as well.     

Evolutionary heritage shapes tree distributions along an Amazon‐to‐Andes elevation gradient

Understanding how evolutionary constraints shape the elevational distributions of tree lineages provides valuable insight into the future of tropical montane forests under global change. With narrow elevational ranges, high taxonomic turnover, frequent habitat specialization, and exceptional levels of endemism, tropical montane forests and trees are predicted to be highly sensitive to environmental change. Using plot census data from a gradient traversing > 3,000 m in elevation on the Amazonian flank of the Peruvian Andes, we employ phylogenetic approaches to assess the influence of evolutionary heritage on distribution trends of trees at the genus‐level. We find that closely related lineages tend to occur at similar mean elevations, with sister genera pairs occurring a mean 254 m in elevation closer to each other than the mean elevational difference between non‐sister genera pairs. We also demonstrate phylogenetic clustering both above and below 1,750 m a.s.l, corresponding roughly to the cloud‐base ecotone. Belying these general trends, some lineages occur across many different elevations. However, these highly plastic lineages are not phylogenetically clustered. Overall, our findings suggest that tropical montane forests are home to unique tree lineage diversity, constrained by their evolutionary heritage and vulnerable to substantial losses under environmental changes, such as rising temperatures or an upward shift of the cloud‐base.